Обсуждение: [ADMIN] WAL archive space planning?
I was "planning" to turn on WAL archiving on a postgresql 9.4.11 server that currently is running with "wal_level=hot_standby" and streaming to a standby. I thought there would be a relationship between the rate of pg_xlog files and archive generation. When I turned up the archive_command/mode I found the scale of the archive target was wrong as I had based it on the pg_xlog file creation rate. When I turned on the archive command for a few minutes, pg_xlog dir contained these files for the time period: -rw------- 1 postgres postgres 16777216 Feb 17 06:47 00000001000023AC0000007F -rw------- 1 postgres postgres 16777216 Feb 17 06:45 00000001000023AC0000007E The archive command wrote 126, 16MB files: -rw------- 1 postgres postgres 16777216 Feb 17 06:47 000000010000237700000056 -rw------- 1 postgres postgres 16777216 Feb 17 06:47 000000010000237700000055 -rw------- 1 postgres postgres 16777216 Feb 17 06:47 000000010000237700000054 -rw------- 1 postgres postgres 16777216 Feb 17 06:47 000000010000237700000053 ... -rw------- 1 postgres postgres 16777216 Feb 17 06:45 0000000100002376000000DC -rw------- 1 postgres postgres 16777216 Feb 17 06:45 0000000100002376000000DB -rw------- 1 postgres postgres 16777216 Feb 17 06:45 0000000100002376000000DA -rw------- 1 postgres postgres 16777216 Feb 17 06:45 0000000100002376000000D9 On servers that are not nearly as busy, I observe a one-to-one relationship between these files/rates. Is there a good WAL archive space planning guide? Is the way to collect planning data for this to turn on wal_debug? TIA!
On Fri, Feb 17, 2017 at 1:30 PM, Ray Stell <stellr@vt.edu> wrote:
I was "planning" to turn on WAL archiving on a postgresql 9.4.11 server that currently is running with "wal_level=hot_standby" and streaming to a standby. I thought there would be a relationship between the rate of pg_xlog files and archive generation. When I turned up the archive_command/mode I found the scale of the archive target was wrong as I had based it on the pg_xlog file creation rate.
When I turned on the archive command for a few minutes, pg_xlog dir contained these files for the time period:
-rw------- 1 postgres postgres 16777216 Feb 17 06:47 00000001000023AC0000007F
-rw------- 1 postgres postgres 16777216 Feb 17 06:45 00000001000023AC0000007E
The archive command wrote 126, 16MB files:
-rw------- 1 postgres postgres 16777216 Feb 17 06:47 000000010000237700000056
-rw------- 1 postgres postgres 16777216 Feb 17 06:47 000000010000237700000055
-rw------- 1 postgres postgres 16777216 Feb 17 06:47 000000010000237700000054
-rw------- 1 postgres postgres 16777216 Feb 17 06:47 000000010000237700000053
...
-rw------- 1 postgres postgres 16777216 Feb 17 06:45 0000000100002376000000DC
-rw------- 1 postgres postgres 16777216 Feb 17 06:45 0000000100002376000000DB
-rw------- 1 postgres postgres 16777216 Feb 17 06:45 0000000100002376000000DA
-rw------- 1 postgres postgres 16777216 Feb 17 06:45 0000000100002376000000D9
On servers that are not nearly as busy, I observe a one-to-one relationship between these files/rates.
Is there a good WAL archive space planning guide?
Is the way to collect planning data for this to turn on wal_debug?
TIA!
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Did you have an archive_timeout value set? This will cause the archive_command to run and create a WAL file at that time interval, no matter how little write activity there may be. These will always be 16MB as well, but if there's no activity, they will compress down quite significantly.
If you disable the timeout, I believe you will then get the matched rate of pg_xlog generation for your archive command.
Keith
check this, his 2nd part introduces Stream Replication Implementation and tell you px_log retention and wal archive related parameters.
2017-02-18 2:30 GMT+08:00 Ray Stell <stellr@vt.edu>:
I was "planning" to turn on WAL archiving on a postgresql 9.4.11 server that currently is running with "wal_level=hot_standby" and streaming to a standby. I thought there would be a relationship between the rate of pg_xlog files and archive generation. When I turned up the archive_command/mode I found the scale of the archive target was wrong as I had based it on the pg_xlog file creation rate.
When I turned on the archive command for a few minutes, pg_xlog dir contained these files for the time period:
-rw------- 1 postgres postgres 16777216 Feb 17 06:47 00000001000023AC0000007F
-rw------- 1 postgres postgres 16777216 Feb 17 06:45 00000001000023AC0000007E
The archive command wrote 126, 16MB files:
-rw------- 1 postgres postgres 16777216 Feb 17 06:47 000000010000237700000056
-rw------- 1 postgres postgres 16777216 Feb 17 06:47 000000010000237700000055
-rw------- 1 postgres postgres 16777216 Feb 17 06:47 000000010000237700000054
-rw------- 1 postgres postgres 16777216 Feb 17 06:47 000000010000237700000053
...
-rw------- 1 postgres postgres 16777216 Feb 17 06:45 0000000100002376000000DC
-rw------- 1 postgres postgres 16777216 Feb 17 06:45 0000000100002376000000DB
-rw------- 1 postgres postgres 16777216 Feb 17 06:45 0000000100002376000000DA
-rw------- 1 postgres postgres 16777216 Feb 17 06:45 0000000100002376000000D9
On servers that are not nearly as busy, I observe a one-to-one relationship between these files/rates.
Is there a good WAL archive space planning guide?
Is the way to collect planning data for this to turn on wal_debug?
TIA!
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On 2/21/17 12:09 AM, Steven Chang wrote:
I'm interested in why I might observed a dramatic difference between pg_xlog files and the archive target files. Other dbs I see have them pretty much one-to-one, but not in this case here. What might cause the large variation? I got only a few pg_xlogs files each minute and 42 archive files/min.check this, his 2nd part introduces Stream Replication Implementation and tell you px_log retention and wal archive related parameters.2017-02-18 2:30 GMT+08:00 Ray Stell <stellr@vt.edu>:I was "planning" to turn on WAL archiving on a postgresql 9.4.11 server that currently is running with "wal_level=hot_standby" and streaming to a standby. I thought there would be a relationship between the rate of pg_xlog files and archive generation. When I turned up the archive_command/mode I found the scale of the archive target was wrong as I had based it on the pg_xlog file creation rate.
When I turned on the archive command for a few minutes, pg_xlog dir contained these files for the time period:
-rw------- 1 postgres postgres 16777216 Feb 17 06:47 00000001000023AC0000007F
-rw------- 1 postgres postgres 16777216 Feb 17 06:45 00000001000023AC0000007E
The archive command wrote 126, 16MB files:
-rw------- 1 postgres postgres 16777216 Feb 17 06:47 000000010000237700000056
-rw------- 1 postgres postgres 16777216 Feb 17 06:47 000000010000237700000055
-rw------- 1 postgres postgres 16777216 Feb 17 06:47 000000010000237700000054
-rw------- 1 postgres postgres 16777216 Feb 17 06:47 000000010000237700000053
...
-rw------- 1 postgres postgres 16777216 Feb 17 06:45 0000000100002376000000DC
-rw------- 1 postgres postgres 16777216 Feb 17 06:45 0000000100002376000000DB
-rw------- 1 postgres postgres 16777216 Feb 17 06:45 0000000100002376000000DA
-rw------- 1 postgres postgres 16777216 Feb 17 06:45 0000000100002376000000D9
On servers that are not nearly as busy, I observe a one-to-one relationship between these files/rates.
Is there a good WAL archive space planning guide?
Is the way to collect planning data for this to turn on wal_debug?
TIA!
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On Tue, Feb 21, 2017 at 12:22 PM, Ray Stell <stellr@vt.edu> wrote:
I'm interested in why I might observed a dramatic difference between pg_xlog files and the archive target files. Other dbs I see have them pretty much one-to-one, but not in this case here. What might cause the large variation? I got only a few pg_xlogs files each minute and 42 archive files/min.On 2/21/17 12:09 AM, Steven Chang wrote:
check this, his 2nd part introduces Stream Replication Implementation and tell you px_log retention and wal archive related parameters.2017-02-18 2:30 GMT+08:00 Ray Stell <stellr@vt.edu>:I was "planning" to turn on WAL archiving on a postgresql 9.4.11 server that currently is running with "wal_level=hot_standby" and streaming to a standby. I thought there would be a relationship between the rate of pg_xlog files and archive generation. When I turned up the archive_command/mode I found the scale of the archive target was wrong as I had based it on the pg_xlog file creation rate.
When I turned on the archive command for a few minutes, pg_xlog dir contained these files for the time period:
-rw------- 1 postgres postgres 16777216 Feb 17 06:47 00000001000023AC0000007F
-rw------- 1 postgres postgres 16777216 Feb 17 06:45 00000001000023AC0000007E
The archive command wrote 126, 16MB files:
-rw------- 1 postgres postgres 16777216 Feb 17 06:47 000000010000237700000056
-rw------- 1 postgres postgres 16777216 Feb 17 06:47 000000010000237700000055
-rw------- 1 postgres postgres 16777216 Feb 17 06:47 000000010000237700000054
-rw------- 1 postgres postgres 16777216 Feb 17 06:47 000000010000237700000053
...
-rw------- 1 postgres postgres 16777216 Feb 17 06:45 0000000100002376000000DC
-rw------- 1 postgres postgres 16777216 Feb 17 06:45 0000000100002376000000DB
-rw------- 1 postgres postgres 16777216 Feb 17 06:45 0000000100002376000000DA
-rw------- 1 postgres postgres 16777216 Feb 17 06:45 0000000100002376000000D9
On servers that are not nearly as busy, I observe a one-to-one relationship between these files/rates.
Is there a good WAL archive space planning guide?
Is the way to collect planning data for this to turn on wal_debug?
TIA!
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Ray,
Did you see my previous response about the archive_timeout setting?
On 2/21/17 12:26 PM, Keith wrote:
On Tue, Feb 21, 2017 at 12:22 PM, Ray Stell <stellr@vt.edu> wrote:I'm interested in why I might observed a dramatic difference between pg_xlog files and the archive target files. Other dbs I see have them pretty much one-to-one, but not in this case here. What might cause the large variation? I got only a few pg_xlogs files each minute and 42 archive files/min.On 2/21/17 12:09 AM, Steven Chang wrote:
check this, his 2nd part introduces Stream Replication Implementation and tell you px_log retention and wal archive related parameters.2017-02-18 2:30 GMT+08:00 Ray Stell <stellr@vt.edu>:I was "planning" to turn on WAL archiving on a postgresql 9.4.11 server that currently is running with "wal_level=hot_standby" and streaming to a standby. I thought there would be a relationship between the rate of pg_xlog files and archive generation. When I turned up the archive_command/mode I found the scale of the archive target was wrong as I had based it on the pg_xlog file creation rate.
When I turned on the archive command for a few minutes, pg_xlog dir contained these files for the time period:
-rw------- 1 postgres postgres 16777216 Feb 17 06:47 00000001000023AC0000007F
-rw------- 1 postgres postgres 16777216 Feb 17 06:45 00000001000023AC0000007E
The archive command wrote 126, 16MB files:
-rw------- 1 postgres postgres 16777216 Feb 17 06:47 000000010000237700000056
-rw------- 1 postgres postgres 16777216 Feb 17 06:47 000000010000237700000055
-rw------- 1 postgres postgres 16777216 Feb 17 06:47 000000010000237700000054
-rw------- 1 postgres postgres 16777216 Feb 17 06:47 000000010000237700000053
...
-rw------- 1 postgres postgres 16777216 Feb 17 06:45 0000000100002376000000DC
-rw------- 1 postgres postgres 16777216 Feb 17 06:45 0000000100002376000000DB
-rw------- 1 postgres postgres 16777216 Feb 17 06:45 0000000100002376000000DA
-rw------- 1 postgres postgres 16777216 Feb 17 06:45 0000000100002376000000D9
On servers that are not nearly as busy, I observe a one-to-one relationship between these files/rates.
Is there a good WAL archive space planning guide?
Is the way to collect planning data for this to turn on wal_debug?
TIA!
--
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http://www.postgresql.org/mailpref/pgsql-admin Ray,Did you see my previous response about the archive_timeout setting?
Lost your post somehow, but I see it in the list archive. Thanks, Keith.
There was a 30 minute timeout set, but I would not think that would increase the archive file generation as observed, does it?
" When this parameter is greater than zero, the server will switch to a new segment file whenever this many seconds have elapsed since the last segment file switch, and there has been any database activity, including a single checkpoint. (Increasing checkpoint_timeout will reduce unnecessary checkpoints on an idle system.) "
Your post seems to indicate having a non-zero value might increase the number of archive files, is that so? Maybe it is in milliseconds which might make sense with the observed archive rate, but the doc says seconds and it was set to 1800. I can set it to 0 and see if it changes things, but I'm a little confused.
On Tue, Feb 21, 2017 at 2:33 PM, Ray Stell <stellr@vt.edu> wrote:
On 2/21/17 12:26 PM, Keith wrote:
Lost your post somehow, but I see it in the list archive. Thanks, Keith.On Tue, Feb 21, 2017 at 12:22 PM, Ray Stell <stellr@vt.edu> wrote:I'm interested in why I might observed a dramatic difference between pg_xlog files and the archive target files. Other dbs I see have them pretty much one-to-one, but not in this case here. What might cause the large variation? I got only a few pg_xlogs files each minute and 42 archive files/min.On 2/21/17 12:09 AM, Steven Chang wrote:
check this, his 2nd part introduces Stream Replication Implementation and tell you px_log retention and wal archive related parameters.2017-02-18 2:30 GMT+08:00 Ray Stell <stellr@vt.edu>:I was "planning" to turn on WAL archiving on a postgresql 9.4.11 server that currently is running with "wal_level=hot_standby" and streaming to a standby. I thought there would be a relationship between the rate of pg_xlog files and archive generation. When I turned up the archive_command/mode I found the scale of the archive target was wrong as I had based it on the pg_xlog file creation rate.
When I turned on the archive command for a few minutes, pg_xlog dir contained these files for the time period:
-rw------- 1 postgres postgres 16777216 Feb 17 06:47 00000001000023AC0000007F
-rw------- 1 postgres postgres 16777216 Feb 17 06:45 00000001000023AC0000007E
The archive command wrote 126, 16MB files:
-rw------- 1 postgres postgres 16777216 Feb 17 06:47 000000010000237700000056
-rw------- 1 postgres postgres 16777216 Feb 17 06:47 000000010000237700000055
-rw------- 1 postgres postgres 16777216 Feb 17 06:47 000000010000237700000054
-rw------- 1 postgres postgres 16777216 Feb 17 06:47 000000010000237700000053
...
-rw------- 1 postgres postgres 16777216 Feb 17 06:45 0000000100002376000000DC
-rw------- 1 postgres postgres 16777216 Feb 17 06:45 0000000100002376000000DB
-rw------- 1 postgres postgres 16777216 Feb 17 06:45 0000000100002376000000DA
-rw------- 1 postgres postgres 16777216 Feb 17 06:45 0000000100002376000000D9
On servers that are not nearly as busy, I observe a one-to-one relationship between these files/rates.
Is there a good WAL archive space planning guide?
Is the way to collect planning data for this to turn on wal_debug?
TIA!
--
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To make changes to your subscription:
http://www.postgresql.org/mailpref/pgsql-admin Ray,Did you see my previous response about the archive_timeout setting?
There was a 30 minute timeout set, but I would not think that would increase the archive file generation as observed, does it?
" When this parameter is greater than zero, the server will switch to a new segment file whenever this many seconds have elapsed since the last segment file switch, and there has been any database activity, including a single checkpoint. (Increasing checkpoint_timeout will reduce unnecessary checkpoints on an idle system.) "
Your post seems to indicate having a non-zero value might increase the number of archive files, is that so? Maybe it is in milliseconds which might make sense with the observed archive rate, but the doc says seconds and it was set to 1800. I can set it to 0 and see if it changes things, but I'm a little confused.
If it was set to 30 minutes, then no, it wouldn't explain what you saw. But we didn't know what it was set to, so that's why I asked. Make sure you're checking the value actually set in the database, and not just what's in postgresql.conf, since it could've changed but never been reloaded to put in place (type "show archive_timeout" in psql).
If that's not it, not sure what may be causing what you're seeing.
If that's not it, not sure what may be causing what you're seeing.
Keith
Dears,
Just read a posgres monitoring moudule named check-postres, which is a ready enhance package on Debian Linux Distribution.
https://bucardo.org/check_postgres/check_postgres.pl.html
here is its readme about wal_files
Maybe you can also use this module to help plan your space usage of WAL files.
wal_files
("symlink: check_postgres_wal_files") Checks how many WAL files exist in the
pg_xlog directory, which is found off of your data_directory, sometimes as a
symlink to another physical disk for performance reasons. This action must be
run as a superuser, in order to access the contents of the pg_xlog directory.
The minimum version to use this action is Postgres 8.1. The --warning and
--critical options are simply the number of files in the pg_xlog directory. What
number to set this to will vary, but a general guideline is to put a number
slightly higher than what is normally there, to catch problems early.
Normally, WAL files are closed and then re-used, but a long-running open
transaction, or a faulty archive_command script, may cause Postgres to create
too many files. Ultimately, this will cause the disk they are on to run out of
space, at which point Postgres will shut down.
2017-02-22 3:45 GMT+08:00 Keith <keith@keithf4.com>:
On Tue, Feb 21, 2017 at 2:33 PM, Ray Stell <stellr@vt.edu> wrote:On 2/21/17 12:26 PM, Keith wrote:
Lost your post somehow, but I see it in the list archive. Thanks, Keith.On Tue, Feb 21, 2017 at 12:22 PM, Ray Stell <stellr@vt.edu> wrote:I'm interested in why I might observed a dramatic difference between pg_xlog files and the archive target files. Other dbs I see have them pretty much one-to-one, but not in this case here. What might cause the large variation? I got only a few pg_xlogs files each minute and 42 archive files/min.On 2/21/17 12:09 AM, Steven Chang wrote:
check this, his 2nd part introduces Stream Replication Implementation and tell you px_log retention and wal archive related parameters.2017-02-18 2:30 GMT+08:00 Ray Stell <stellr@vt.edu>:I was "planning" to turn on WAL archiving on a postgresql 9.4.11 server that currently is running with "wal_level=hot_standby" and streaming to a standby. I thought there would be a relationship between the rate of pg_xlog files and archive generation. When I turned up the archive_command/mode I found the scale of the archive target was wrong as I had based it on the pg_xlog file creation rate.
When I turned on the archive command for a few minutes, pg_xlog dir contained these files for the time period:
-rw------- 1 postgres postgres 16777216 Feb 17 06:47 00000001000023AC0000007F
-rw------- 1 postgres postgres 16777216 Feb 17 06:45 00000001000023AC0000007E
The archive command wrote 126, 16MB files:
-rw------- 1 postgres postgres 16777216 Feb 17 06:47 000000010000237700000056
-rw------- 1 postgres postgres 16777216 Feb 17 06:47 000000010000237700000055
-rw------- 1 postgres postgres 16777216 Feb 17 06:47 000000010000237700000054
-rw------- 1 postgres postgres 16777216 Feb 17 06:47 000000010000237700000053
...
-rw------- 1 postgres postgres 16777216 Feb 17 06:45 0000000100002376000000DC
-rw------- 1 postgres postgres 16777216 Feb 17 06:45 0000000100002376000000DB
-rw------- 1 postgres postgres 16777216 Feb 17 06:45 0000000100002376000000DA
-rw------- 1 postgres postgres 16777216 Feb 17 06:45 0000000100002376000000D9
On servers that are not nearly as busy, I observe a one-to-one relationship between these files/rates.
Is there a good WAL archive space planning guide?
Is the way to collect planning data for this to turn on wal_debug?
TIA!
--
Sent via pgsql-admin mailing list (pgsql-admin@postgresql.org)
To make changes to your subscription:
http://www.postgresql.org/mailpref/pgsql-admin Ray,Did you see my previous response about the archive_timeout setting?
There was a 30 minute timeout set, but I would not think that would increase the archive file generation as observed, does it?
" When this parameter is greater than zero, the server will switch to a new segment file whenever this many seconds have elapsed since the last segment file switch, and there has been any database activity, including a single checkpoint. (Increasing checkpoint_timeout will reduce unnecessary checkpoints on an idle system.) "
Your post seems to indicate having a non-zero value might increase the number of archive files, is that so? Maybe it is in milliseconds which might make sense with the observed archive rate, but the doc says seconds and it was set to 1800. I can set it to 0 and see if it changes things, but I'm a little confused.If it was set to 30 minutes, then no, it wouldn't explain what you saw. But we didn't know what it was set to, so that's why I asked. Make sure you're checking the value actually set in the database, and not just what's in postgresql.conf, since it could've changed but never been reloaded to put in place (type "show archive_timeout" in psql).
If that's not it, not sure what may be causing what you're seeing.Keith
Forgive me if this has been explained well in the past. You can probably search my name for discussions on this...
I fail to see why WAL archiving is either required or desired in a streaming replication scenario WHERE ONE NEVER NEEDS PITR.
I have 2 "production" servers. One is paid customers, and one is customer-facing test and training. Let us call the one that I care about bigDb and the other littleDb.
littleDb replicates bigDb in real-time. They both back up nightly. They are in the same data center.
At my home office, I have otherDb which replicates BOTH and runs independent backups nightly.
I have to have a secondary data center. Let's call that otherCityBigDb and otherCityLittleDb. They stream replication.
There is nowhere in the world where I am responsible for rolling back to anything.
Why would one EVER want WAL archiving? It seems like you are planning for failure.
On Mar 13, 2017 10:55 PM, Steven Chang <stevenchang1213@gmail.com> wrote:
Dears,Just read a posgres monitoring moudule named check-postres, which is a ready enhance package on Debian Linux Distribution.https://bucardo.org/check_postgres/check_postgres.pl.htmlhere is its readme about wal_filesMaybe you can also use this module to help plan your space usage of WAL files.wal_files("symlink: check_postgres_wal_files") Checks how many WAL files exist in thepg_xlog directory, which is found off of your data_directory, sometimes as asymlink to another physical disk for performance reasons. This action must berun as a superuser, in order to access the contents of the pg_xlog directory.The minimum version to use this action is Postgres 8.1. The --warning and--critical options are simply the number of files in the pg_xlog directory. Whatnumber to set this to will vary, but a general guideline is to put a numberslightly higher than what is normally there, to catch problems early.Normally, WAL files are closed and then re-used, but a long-running opentransaction, or a faulty archive_command script, may cause Postgres to createtoo many files. Ultimately, this will cause the disk they are on to run out ofspace, at which point Postgres will shut down.2017-02-22 3:45 GMT+08:00 Keith <keith@keithf4.com>:On Tue, Feb 21, 2017 at 2:33 PM, Ray Stell <stellr@vt.edu> wrote:On 2/21/17 12:26 PM, Keith wrote:
Lost your post somehow, but I see it in the list archive. Thanks, Keith.On Tue, Feb 21, 2017 at 12:22 PM, Ray Stell <stellr@vt.edu> wrote:I'm interested in why I might observed a dramatic difference between pg_xlog files and the archive target files. Other dbs I see have them pretty much one-to-one, but not in this case here. What might cause the large variation? I got only a few pg_xlogs files each minute and 42 archive files/min.On 2/21/17 12:09 AM, Steven Chang wrote:
check this, his 2nd part introduces Stream Replication Implementation and tell you px_log retention and wal archive related parameters.2017-02-18 2:30 GMT+08:00 Ray Stell <stellr@vt.edu>:I was "planning" to turn on WAL archiving on a postgresql 9.4.11 server that currently is running with "wal_level=hot_standby" and streaming to a standby. I thought there would be a relationship between the rate of pg_xlog files and archive generation. When I turned up the archive_command/mode I found the scale of the archive target was wrong as I had based it on the pg_xlog file creation rate.
When I turned on the archive command for a few minutes, pg_xlog dir contained these files for the time period:
-rw------- 1 postgres postgres 16777216 Feb 17 06:47 00000001000023AC0000007F
-rw------- 1 postgres postgres 16777216 Feb 17 06:45 00000001000023AC0000007E
The archive command wrote 126, 16MB files:
-rw------- 1 postgres postgres 16777216 Feb 17 06:47 000000010000237700000056
-rw------- 1 postgres postgres 16777216 Feb 17 06:47 000000010000237700000055
-rw------- 1 postgres postgres 16777216 Feb 17 06:47 000000010000237700000054
-rw------- 1 postgres postgres 16777216 Feb 17 06:47 000000010000237700000053
...
-rw------- 1 postgres postgres 16777216 Feb 17 06:45 0000000100002376000000DC
-rw------- 1 postgres postgres 16777216 Feb 17 06:45 0000000100002376000000DB
-rw------- 1 postgres postgres 16777216 Feb 17 06:45 0000000100002376000000DA
-rw------- 1 postgres postgres 16777216 Feb 17 06:45 0000000100002376000000D9
On servers that are not nearly as busy, I observe a one-to-one relationship between these files/rates.
Is there a good WAL archive space planning guide?
Is the way to collect planning data for this to turn on wal_debug?
TIA!
--
Sent via pgsql-admin mailing list (pgsql-admin@postgresql.org)
To make changes to your subscription:
http://www.postgresql.org/mailpref/pgsql-admin Ray,Did you see my previous response about the archive_timeout setting?
There was a 30 minute timeout set, but I would not think that would increase the archive file generation as observed, does it?
" When this parameter is greater than zero, the server will switch to a new segment file whenever this many seconds have elapsed since the last segment file switch, and there has been any database activity, including a single checkpoint. (Increasing checkpoint_timeout will reduce unnecessary checkpoints on an idle system.) "
Your post seems to indicate having a non-zero value might increase the number of archive files, is that so? Maybe it is in milliseconds which might make sense with the observed archive rate, but the doc says seconds and it was set to 1800. I can set it to 0 and see if it changes things, but I'm a little confused.If it was set to 30 minutes, then no, it wouldn't explain what you saw. But we didn't know what it was set to, so that's why I asked. Make sure you're checking the value actually set in the database, and not just what's in postgresql.conf, since it could've changed but never been reloaded to put in place (type "show archive_timeout" in psql).
If that's not it, not sure what may be causing what you're seeing.Keith
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Hi Scott,
Do you have any experience on any RDBMS other than postgres ?
And this page explains it very much about WAL ---- https://www.postgresql.org/
Replication is actually a disaster recovery solution, but now many other experts extend it to function others.
For example, combining with pgpool, it could distribute offload select query to slave sites for scale or performance concerns.
Of course you could also coding plproxy to accomplish the same goal.
Best Regards,
Steven
2017-03-14 12:17 GMT+08:00 Scott Whitney <scott@journyx.com>:
Forgive me if this has been explained well in the past. You can probably search my name for discussions on this...I fail to see why WAL archiving is either required or desired in a streaming replication scenario WHERE ONE NEVER NEEDS PITR.I have 2 "production" servers. One is paid customers, and one is customer-facing test and training. Let us call the one that I care about bigDb and the other littleDb.littleDb replicates bigDb in real-time. They both back up nightly. They are in the same data center.At my home office, I have otherDb which replicates BOTH and runs independent backups nightly.I have to have a secondary data center. Let's call that otherCityBigDb and otherCityLittleDb. They stream replication.There is nowhere in the world where I am responsible for rolling back to anything.Why would one EVER want WAL archiving? It seems like you are planning for failure.On Mar 13, 2017 10:55 PM, Steven Chang <stevenchang1213@gmail.com> wrote:Dears,Just read a posgres monitoring moudule named check-postres, which is a ready enhance package on Debian Linux Distribution.https://bucardo.org/check_postgres/check_postgres.pl. html here is its readme about wal_filesMaybe you can also use this module to help plan your space usage of WAL files.wal_files("symlink: check_postgres_wal_files") Checks how many WAL files exist in thepg_xlog directory, which is found off of your data_directory, sometimes as asymlink to another physical disk for performance reasons. This action must berun as a superuser, in order to access the contents of the pg_xlog directory.The minimum version to use this action is Postgres 8.1. The --warning and--critical options are simply the number of files in the pg_xlog directory. Whatnumber to set this to will vary, but a general guideline is to put a numberslightly higher than what is normally there, to catch problems early.Normally, WAL files are closed and then re-used, but a long-running opentransaction, or a faulty archive_command script, may cause Postgres to createtoo many files. Ultimately, this will cause the disk they are on to run out ofspace, at which point Postgres will shut down.2017-02-22 3:45 GMT+08:00 Keith <keith@keithf4.com>:On Tue, Feb 21, 2017 at 2:33 PM, Ray Stell <stellr@vt.edu> wrote:On 2/21/17 12:26 PM, Keith wrote:
Lost your post somehow, but I see it in the list archive. Thanks, Keith.On Tue, Feb 21, 2017 at 12:22 PM, Ray Stell <stellr@vt.edu> wrote:I'm interested in why I might observed a dramatic difference between pg_xlog files and the archive target files. Other dbs I see have them pretty much one-to-one, but not in this case here. What might cause the large variation? I got only a few pg_xlogs files each minute and 42 archive files/min.On 2/21/17 12:09 AM, Steven Chang wrote:
check this, his 2nd part introduces Stream Replication Implementation and tell you px_log retention and wal archive related parameters.2017-02-18 2:30 GMT+08:00 Ray Stell <stellr@vt.edu>:I was "planning" to turn on WAL archiving on a postgresql 9.4.11 server that currently is running with "wal_level=hot_standby" and streaming to a standby. I thought there would be a relationship between the rate of pg_xlog files and archive generation. When I turned up the archive_command/mode I found the scale of the archive target was wrong as I had based it on the pg_xlog file creation rate.
When I turned on the archive command for a few minutes, pg_xlog dir contained these files for the time period:
-rw------- 1 postgres postgres 16777216 Feb 17 06:47 00000001000023AC0000007F
-rw------- 1 postgres postgres 16777216 Feb 17 06:45 00000001000023AC0000007E
The archive command wrote 126, 16MB files:
-rw------- 1 postgres postgres 16777216 Feb 17 06:47 000000010000237700000056
-rw------- 1 postgres postgres 16777216 Feb 17 06:47 000000010000237700000055
-rw------- 1 postgres postgres 16777216 Feb 17 06:47 000000010000237700000054
-rw------- 1 postgres postgres 16777216 Feb 17 06:47 000000010000237700000053
...
-rw------- 1 postgres postgres 16777216 Feb 17 06:45 0000000100002376000000DC
-rw------- 1 postgres postgres 16777216 Feb 17 06:45 0000000100002376000000DB
-rw------- 1 postgres postgres 16777216 Feb 17 06:45 0000000100002376000000DA
-rw------- 1 postgres postgres 16777216 Feb 17 06:45 0000000100002376000000D9
On servers that are not nearly as busy, I observe a one-to-one relationship between these files/rates.
Is there a good WAL archive space planning guide?
Is the way to collect planning data for this to turn on wal_debug?
TIA!
--
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To make changes to your subscription:
http://www.postgresql.org/mailpref/pgsql-admin Ray,Did you see my previous response about the archive_timeout setting?
There was a 30 minute timeout set, but I would not think that would increase the archive file generation as observed, does it?
" When this parameter is greater than zero, the server will switch to a new segment file whenever this many seconds have elapsed since the last segment file switch, and there has been any database activity, including a single checkpoint. (Increasing checkpoint_timeout will reduce unnecessary checkpoints on an idle system.) "
Your post seems to indicate having a non-zero value might increase the number of archive files, is that so? Maybe it is in milliseconds which might make sense with the observed archive rate, but the doc says seconds and it was set to 1800. I can set it to 0 and see if it changes things, but I'm a little confused.If it was set to 30 minutes, then no, it wouldn't explain what you saw. But we didn't know what it was set to, so that's why I asked. Make sure you're checking the value actually set in the database, and not just what's in postgresql.conf, since it could've changed but never been reloaded to put in place (type "show archive_timeout" in psql).
If that's not it, not sure what may be causing what you're seeing.KeithJournyx, Inc.Do you receive our promotional emails? You can subscribe or unsubscribe to those emails at http://go.journyx.com/emailPreference/e/4932/714/
On 3/13/17 11:53 PM, Steven Chang wrote:
Thanks, Steven,Dears,Just read a posgres monitoring moudule named check-postres, which is a ready enhance package on Debian Linux Distribution.https://bucardo.org/check_postgres/check_postgres.pl.htmlhere is its readme about wal_filesMaybe you can also use this module to help plan your space usage of WAL files.wal_files("symlink: check_postgres_wal_files") Checks how many WAL files exist in thepg_xlog directory, which is found off of your data_directory, sometimes as asymlink to another physical disk for performance reasons. This action must berun as a superuser, in order to access the contents of the pg_xlog directory.The minimum version to use this action is Postgres 8.1. The --warning and--critical options are simply the number of files in the pg_xlog directory. Whatnumber to set this to will vary, but a general guideline is to put a numberslightly higher than what is normally there, to catch problems early.Normally, WAL files are closed and then re-used, but a long-running opentransaction, or a faulty archive_command script, may cause Postgres to createtoo many files. Ultimately, this will cause the disk they are on to run out ofspace, at which point Postgres will shut down.2017-02-22 3:45 GMT+08:00 Keith <keith@keithf4.com>:On Tue, Feb 21, 2017 at 2:33 PM, Ray Stell <stellr@vt.edu> wrote:On 2/21/17 12:26 PM, Keith wrote:
Lost your post somehow, but I see it in the list archive. Thanks, Keith.On Tue, Feb 21, 2017 at 12:22 PM, Ray Stell <stellr@vt.edu> wrote:I'm interested in why I might observed a dramatic difference between pg_xlog files and the archive target files. Other dbs I see have them pretty much one-to-one, but not in this case here. What might cause the large variation? I got only a few pg_xlogs files each minute and 42 archive files/min.On 2/21/17 12:09 AM, Steven Chang wrote:
check this, his 2nd part introduces Stream Replication Implementation and tell you px_log retention and wal archive related parameters.2017-02-18 2:30 GMT+08:00 Ray Stell <stellr@vt.edu>:I was "planning" to turn on WAL archiving on a postgresql 9.4.11 server that currently is running with "wal_level=hot_standby" and streaming to a standby. I thought there would be a relationship between the rate of pg_xlog files and archive generation. When I turned up the archive_command/mode I found the scale of the archive target was wrong as I had based it on the pg_xlog file creation rate.
When I turned on the archive command for a few minutes, pg_xlog dir contained these files for the time period:
-rw------- 1 postgres postgres 16777216 Feb 17 06:47 00000001000023AC0000007F
-rw------- 1 postgres postgres 16777216 Feb 17 06:45 00000001000023AC0000007E
The archive command wrote 126, 16MB files:
-rw------- 1 postgres postgres 16777216 Feb 17 06:47 000000010000237700000056
-rw------- 1 postgres postgres 16777216 Feb 17 06:47 000000010000237700000055
-rw------- 1 postgres postgres 16777216 Feb 17 06:47 000000010000237700000054
-rw------- 1 postgres postgres 16777216 Feb 17 06:47 000000010000237700000053
...
-rw------- 1 postgres postgres 16777216 Feb 17 06:45 0000000100002376000000DC
-rw------- 1 postgres postgres 16777216 Feb 17 06:45 0000000100002376000000DB
-rw------- 1 postgres postgres 16777216 Feb 17 06:45 0000000100002376000000DA
-rw------- 1 postgres postgres 16777216 Feb 17 06:45 0000000100002376000000D9
On servers that are not nearly as busy, I observe a one-to-one relationship between these files/rates.
Is there a good WAL archive space planning guide?
Is the way to collect planning data for this to turn on wal_debug?
TIA!
--
Sent via pgsql-admin mailing list (pgsql-admin@postgresql.org)
To make changes to your subscription:
http://www.postgresql.org/mailpref/pgsql-admin Ray,Did you see my previous response about the archive_timeout setting?
There was a 30 minute timeout set, but I would not think that would increase the archive file generation as observed, does it?
" When this parameter is greater than zero, the server will switch to a new segment file whenever this many seconds have elapsed since the last segment file switch, and there has been any database activity, including a single checkpoint. (Increasing checkpoint_timeout will reduce unnecessary checkpoints on an idle system.) "
Your post seems to indicate having a non-zero value might increase the number of archive files, is that so? Maybe it is in milliseconds which might make sense with the observed archive rate, but the doc says seconds and it was set to 1800. I can set it to 0 and see if it changes things, but I'm a little confused.If it was set to 30 minutes, then no, it wouldn't explain what you saw. But we didn't know what it was set to, so that's why I asked. Make sure you're checking the value actually set in the database, and not just what's in postgresql.conf, since it could've changed but never been reloaded to put in place (type "show archive_timeout" in psql).
If that's not it, not sure what may be causing what you're seeing.Keith
An interesting statement:
"long-running open transaction, or a faulty archive_command script, may cause Postgres to create too many files. Ultimately, this will cause the disk they are on to run out of space, at which point Postgres will shut down."
The statement, "long-running open transaction...may cause Postgres to create too many files" makes it sound like there could be the case where there is not a 1-to-1 relationship between pg_xlog and the archive. I've never seen that before and didn't think that was the case. Maybe I'm reading too much into the statement.
I have to suspect that the "faulty" nature of the archive_command was that it was just asking too much of the I/O subsystem and was just getting way behind. Shockingly way behind. I didn't expect it. It is a very busy system will many long running transactions. If I ever get back to that problem, my first pass will be to reduce the load request. I suppose I can do some bonnie tests to simulate the archive writing. I was doing some multiplexing of the files in the archive shell. Let's see what writing them once locally does first. If it can't do that and keep up, I'm going to need a "bigger boat." It's a production system so I only get a few cracks at it a year. I'll probably wait for the next patch release. Going back to the last backup is within the SLA, but I don't like not having the archive.
On 3/14/17 12:17 AM, Scott Whitney wrote:
Forgive me if this has been explained well in the past. You can probably search my name for discussions on this...I fail to see why WAL archiving is either required or desired in a streaming replication scenario WHERE ONE NEVER NEEDS PITR.I have 2 "production" servers. One is paid customers, and one is customer-facing test and training. Let us call the one that I care about bigDb and the other littleDb.littleDb replicates bigDb in real-time. They both back up nightly. They are in the same data center.At my home office, I have otherDb which replicates BOTH and runs independent backups nightly.I have to have a secondary data center. Let's call that otherCityBigDb and otherCityLittleDb. They stream replication.There is nowhere in the world where I am responsible for rolling back to anything.Why would one EVER want WAL archiving? It seems like you are planning for failure.On Mar 13, 2017 10:55 PM, Steven Chang <stevenchang1213@gmail.com> wrote:Dears,Just read a posgres monitoring moudule named check-postres, which is a ready enhance package on Debian Linux Distribution.https://bucardo.org/check_postgres/check_postgres.pl.htmlhere is its readme about wal_filesMaybe you can also use this module to help plan your space usage of WAL files.wal_files("symlink: check_postgres_wal_files") Checks how many WAL files exist in thepg_xlog directory, which is found off of your data_directory, sometimes as asymlink to another physical disk for performance reasons. This action must berun as a superuser, in order to access the contents of the pg_xlog directory.The minimum version to use this action is Postgres 8.1. The --warning and--critical options are simply the number of files in the pg_xlog directory. Whatnumber to set this to will vary, but a general guideline is to put a numberslightly higher than what is normally there, to catch problems early.Normally, WAL files are closed and then re-used, but a long-running opentransaction, or a faulty archive_command script, may cause Postgres to createtoo many files. Ultimately, this will cause the disk they are on to run out ofspace, at which point Postgres will shut down.2017-02-22 3:45 GMT+08:00 Keith <keith@keithf4.com>:On Tue, Feb 21, 2017 at 2:33 PM, Ray Stell <stellr@vt.edu> wrote:On 2/21/17 12:26 PM, Keith wrote:
Lost your post somehow, but I see it in the list archive. Thanks, Keith.On Tue, Feb 21, 2017 at 12:22 PM, Ray Stell <stellr@vt.edu> wrote:I'm interested in why I might observed a dramatic difference between pg_xlog files and the archive target files. Other dbs I see have them pretty much one-to-one, but not in this case here. What might cause the large variation? I got only a few pg_xlogs files each minute and 42 archive files/min.On 2/21/17 12:09 AM, Steven Chang wrote:
check this, his 2nd part introduces Stream Replication Implementation and tell you px_log retention and wal archive related parameters.2017-02-18 2:30 GMT+08:00 Ray Stell <stellr@vt.edu>:I was "planning" to turn on WAL archiving on a postgresql 9.4.11 server that currently is running with "wal_level=hot_standby" and streaming to a standby. I thought there would be a relationship between the rate of pg_xlog files and archive generation. When I turned up the archive_command/mode I found the scale of the archive target was wrong as I had based it on the pg_xlog file creation rate.
When I turned on the archive command for a few minutes, pg_xlog dir contained these files for the time period:
-rw------- 1 postgres postgres 16777216 Feb 17 06:47 00000001000023AC0000007F
-rw------- 1 postgres postgres 16777216 Feb 17 06:45 00000001000023AC0000007E
The archive command wrote 126, 16MB files:
-rw------- 1 postgres postgres 16777216 Feb 17 06:47 000000010000237700000056
-rw------- 1 postgres postgres 16777216 Feb 17 06:47 000000010000237700000055
-rw------- 1 postgres postgres 16777216 Feb 17 06:47 000000010000237700000054
-rw------- 1 postgres postgres 16777216 Feb 17 06:47 000000010000237700000053
...
-rw------- 1 postgres postgres 16777216 Feb 17 06:45 0000000100002376000000DC
-rw------- 1 postgres postgres 16777216 Feb 17 06:45 0000000100002376000000DB
-rw------- 1 postgres postgres 16777216 Feb 17 06:45 0000000100002376000000DA
-rw------- 1 postgres postgres 16777216 Feb 17 06:45 0000000100002376000000D9
On servers that are not nearly as busy, I observe a one-to-one relationship between these files/rates.
Is there a good WAL archive space planning guide?
Is the way to collect planning data for this to turn on wal_debug?
TIA!
--
Sent via pgsql-admin mailing list (pgsql-admin@postgresql.org)
To make changes to your subscription:
http://www.postgresql.org/mailpref/pgsql-admin Ray,Did you see my previous response about the archive_timeout setting?
There was a 30 minute timeout set, but I would not think that would increase the archive file generation as observed, does it?
" When this parameter is greater than zero, the server will switch to a new segment file whenever this many seconds have elapsed since the last segment file switch, and there has been any database activity, including a single checkpoint. (Increasing checkpoint_timeout will reduce unnecessary checkpoints on an idle system.) "
Your post seems to indicate having a non-zero value might increase the number of archive files, is that so? Maybe it is in milliseconds which might make sense with the observed archive rate, but the doc says seconds and it was set to 1800. I can set it to 0 and see if it changes things, but I'm a little confused.If it was set to 30 minutes, then no, it wouldn't explain what you saw. But we didn't know what it was set to, so that's why I asked. Make sure you're checking the value actually set in the database, and not just what's in postgresql.conf, since it could've changed but never been reloaded to put in place (type "show archive_timeout" in psql).
If that's not it, not sure what may be causing what you're seeing.KeithJournyx, Inc.p 512.834.8888f 512-834-8858Do you receive our promotional emails? You can subscribe or unsubscribe to those emails at http://go.journyx.com/emailPreference/e/4932/714/
"There is nowhere in the world where I am responsible for rolling back to anything."
Logical failures. Suppose duhveloper trashes table on production when he meant to make the change to pre-prod. I might want to roll forward to to a PIT just before.
Scott Whitney <scott@journyx.com> writes: > Forgive me if this has been explained well in the past. You can probably search my name for discussions on this... > > I fail to see why WAL archiving is either required or desired in a streaming replication scenario WHERE ONE NEVER NEEDSPITR. If you don't mind losing sync from standby to master and having to refresh the standby from scratch after for any reason streaming connectivity is lost (and/or standby falls out of sync due to a too heavy volume)... then fine. In practice you need both to allow standbys to catch up again after an a break. A busy master can overrun a streaming standby at times just due to volume, perhaps complicated by IO throughput on the standby. Your standby may go down undetected... it may lag beyond what the master still has in pg_xlog to satisfy simply due to configured in replication lag tolerance to support reporting workloads. To name a few :-) True in an uncomplicated setup being able to fetch WALs from a remote archive site is not strictly necessary. It's also the case with newer Pg releases, that if you use a binary rep slot, your master will hold WAL forever in its own pg_xlog directory until a down standby comes alive and reads the data but then your production master is at risk of disk filling if the unresponsive standby isn't dealt with eventually. HTH > I have 2 "production" servers. One is paid customers, and one is customer-facing test and training. Let us call the onethat I care about bigDb and the other littleDb. > > littleDb replicates bigDb in real-time. They both back up nightly. They are in the same data center. > > At my home office, I have otherDb which replicates BOTH and runs independent backups nightly. > > I have to have a secondary data center. Let's call that otherCityBigDb and otherCityLittleDb. They stream replication. > > There is nowhere in the world where I am responsible for rolling back to anything. > > Why would one EVER want WAL archiving? It seems like you are planning for failure. > > On Mar 13, 2017 10:55 PM, Steven Chang <stevenchang1213@gmail.com> wrote: > > Dears, > > Just read a posgres monitoring moudule named check-postres, which is a ready enhance package on Debian LinuxDistribution. > > https://bucardo.org/check_postgres/check_postgres.pl.html > > here is its readme about wal_files > Maybe you can also use this module to help plan your space usage of WAL files. > > wal_files > ("symlink: check_postgres_wal_files") Checks how many WAL files exist in the > pg_xlog directory, which is found off of your data_directory, sometimes as a > symlink to another physical disk for performance reasons. This action must be > run as a superuser, in order to access the contents of the pg_xlog directory. > The minimum version to use this action is Postgres 8.1. The --warning and > --critical options are simply the number of files in the pg_xlog directory. What > number to set this to will vary, but a general guideline is to put a number > slightly higher than what is normally there, to catch problems early. > > Normally, WAL files are closed and then re-used, but a long-running open > transaction, or a faulty archive_command script, may cause Postgres to create > too many files. Ultimately, this will cause the disk they are on to run out of > space, at which point Postgres will shut down. > > 2017-02-22 3:45 GMT+08:00 Keith <keith@keithf4.com>: > > On Tue, Feb 21, 2017 at 2:33 PM, Ray Stell <stellr@vt.edu> wrote: > > On 2/21/17 12:26 PM, Keith wrote: > > On Tue, Feb 21, 2017 at 12:22 PM, Ray Stell <stellr@vt.edu> wrote: > > On 2/21/17 12:09 AM, Steven Chang wrote: > > check this, his 2nd part introduces Stream Replication Implementation and tell you px_log retentionand wal archive related parameters. > https://www.itenlight.com/blog/2016/05/19/PostgreSQL+HA+with+pgpool-II+-+Part+2 > > 2017-02-18 2:30 GMT+08:00 Ray Stell <stellr@vt.edu>: > > I was "planning" to turn on WAL archiving on a postgresql 9.4.11 server that currently is runningwith "wal_level=hot_standby" and streaming > to a standby. I thought there would be a relationship between the rate of pg_xlog files andarchive generation. When I turned up the > archive_command/mode I found the scale of the archive target was wrong as I had based it onthe pg_xlog file creation rate. > > When I turned on the archive command for a few minutes, pg_xlog dir contained these files forthe time period: > > -rw------- 1 postgres postgres 16777216 Feb 17 06:47 00000001000023AC0000007F > -rw------- 1 postgres postgres 16777216 Feb 17 06:45 00000001000023AC0000007E > > The archive command wrote 126, 16MB files: > > -rw------- 1 postgres postgres 16777216 Feb 17 06:47 000000010000237700000056 > -rw------- 1 postgres postgres 16777216 Feb 17 06:47 000000010000237700000055 > -rw------- 1 postgres postgres 16777216 Feb 17 06:47 000000010000237700000054 > -rw------- 1 postgres postgres 16777216 Feb 17 06:47 000000010000237700000053 > ... > > -rw------- 1 postgres postgres 16777216 Feb 17 06:45 0000000100002376000000DC > -rw------- 1 postgres postgres 16777216 Feb 17 06:45 0000000100002376000000DB > -rw------- 1 postgres postgres 16777216 Feb 17 06:45 0000000100002376000000DA > -rw------- 1 postgres postgres 16777216 Feb 17 06:45 0000000100002376000000D9 > > On servers that are not nearly as busy, I observe a one-to-one relationship between these files/rates. > > Is there a good WAL archive space planning guide? > > Is the way to collect planning data for this to turn on wal_debug? > > TIA! > > -- > Sent via pgsql-admin mailing list (pgsql-admin@postgresql.org) > To make changes to your subscription: > http://www.postgresql.org/mailpref/pgsql-admin > > I'm interested in why I might observed a dramatic difference between pg_xlog files and the archivetarget files. Other dbs I see have them pretty > much one-to-one, but not in this case here. What might cause the large variation? I got only a fewpg_xlogs files each minute and 42 archive files > /min. > > Ray, > > Did you see my previous response about the archive_timeout setting? > > Lost your post somehow, but I see it in the list archive. Thanks, Keith. > > There was a 30 minute timeout set, but I would not think that would increase the archive file generation asobserved, does it? > > " When this parameter is greater than zero, the server will switch to a new segment file whenever this manyseconds have elapsed since the last segment file > switch, and there has been any database activity, including a single checkpoint. (Increasing checkpoint_timeoutwill reduce unnecessary checkpoints on an > idle system.) " > > Your post seems to indicate having a non-zero value might increase the number of archive files, is that so? Maybe it is in milliseconds which might make > sense with the observed archive rate, but the doc says seconds and it was set to 1800. I can set it to 0 andsee if it changes things, but I'm a little > confused. > > If it was set to 30 minutes, then no, it wouldn't explain what you saw. But we didn't know what it was set to,so that's why I asked. Make sure you're checking > the value actually set in the database, and not just what's in postgresql.conf, since it could've changed but neverbeen reloaded to put in place (type "show > archive_timeout" in psql). > > If that's not it, not sure what may be causing what you're seeing. > > Keith > > Journyx, Inc. > 7600 Burnet Road #300 > Austin, TX 78757 > www.journyx.com > > p 512.834.8888 > f 512-834-8858 > > Do you receive our promotional emails? You can subscribe or unsubscribe to those emails at http://go.journyx.com/emailPreference/e/4932/714/ > -- Jerry Sievers Postgres DBA/Development Consulting e: postgres.consulting@comcast.net p: 312.241.7800
Hello,
Official documents (since 7.2) do give us some formulation to evaluate the space usage of WAL files.
It also depends on your how your environment configured.
There will always be at least one WAL segment file, and will normally not be more than (2 + checkpoint_completion_target) * checkpoint_segments + 1 or checkpoint_segments + wal_keep_segments + 1 files. Each segment file is normally 16 MB (though this size can be altered when building the server). You can use this to estimate space requirements for WAL. Ordinarily, when old log segment files are no longer needed, they are recycled (that is, renamed to become future segments in the numbered sequence). If, due to a short-term peak of log output rate, there are more than 3 * checkpoint_segments + 1 segment files, the unneeded segment files will be deleted instead of recycled until the system gets back under this limit.
2. https://www.postgresql.org/docs/9.4/static/continuous-archiving.html
It is important that the archive command return zero exit status if and only if it succeeds. Upon getting a zero result, PostgreSQL will assume that the file has been successfully archived, and will remove or recycle it. However, a nonzero status tells PostgreSQL that the file was not archived; it will try again periodically until it succeeds.
BR,
Steven
2017-03-18 5:39 GMT+08:00 Jerry Sievers <gsievers19@comcast.net>:
Scott Whitney <scott@journyx.com> writes:
> Forgive me if this has been explained well in the past. You can probably search my name for discussions on this...
>
> I fail to see why WAL archiving is either required or desired in a streaming replication scenario WHERE ONE NEVER NEEDS PITR.
If you don't mind losing sync from standby to master and having to
refresh the standby from scratch after for any reason streaming
connectivity is lost (and/or standby falls out of sync due to a too
heavy volume)... then fine.
In practice you need both to allow standbys to catch up again after an a
break.
A busy master can overrun a streaming standby at times just due to
volume, perhaps complicated by IO throughput on the standby.
Your standby may go down undetected... it may lag beyond what the
master still has in pg_xlog to satisfy simply due to configured in
replication lag tolerance to support reporting workloads.
To name a few :-)
True in an uncomplicated setup being able to fetch WALs from a remote
archive site is not strictly necessary.
It's also the case with newer Pg releases, that if you use a binary rep
slot, your master will hold WAL forever in its own pg_xlog directory
until a down standby comes alive and reads the data but then your
production master is at risk of disk filling if the unresponsive standby
isn't dealt with eventually.
HTH--
> I have 2 "production" servers. One is paid customers, and one is customer-facing test and training. Let us call the one that I care about bigDb and the other littleDb.
>
> littleDb replicates bigDb in real-time. They both back up nightly. They are in the same data center.
>
> At my home office, I have otherDb which replicates BOTH and runs independent backups nightly.
>
> I have to have a secondary data center. Let's call that otherCityBigDb and otherCityLittleDb. They stream replication.
>
> There is nowhere in the world where I am responsible for rolling back to anything.
>
> Why would one EVER want WAL archiving? It seems like you are planning for failure.
>
> On Mar 13, 2017 10:55 PM, Steven Chang <stevenchang1213@gmail.com> wrote:
>
> Dears,
>
> Just read a posgres monitoring moudule named check-postres, which is a ready enhance package on Debian Linux Distribution.
>
> https://bucardo.org/check_postgres/check_postgres.pl. html
>
> here is its readme about wal_files
> Maybe you can also use this module to help plan your space usage of WAL files.
>
> wal_files
> ("symlink: check_postgres_wal_files") Checks how many WAL files exist in the
> pg_xlog directory, which is found off of your data_directory, sometimes as a
> symlink to another physical disk for performance reasons. This action must be
> run as a superuser, in order to access the contents of the pg_xlog directory.
> The minimum version to use this action is Postgres 8.1. The --warning and
> --critical options are simply the number of files in the pg_xlog directory. What
> number to set this to will vary, but a general guideline is to put a number
> slightly higher than what is normally there, to catch problems early.
>
> Normally, WAL files are closed and then re-used, but a long-running open
> transaction, or a faulty archive_command script, may cause Postgres to create
> too many files. Ultimately, this will cause the disk they are on to run out of
> space, at which point Postgres will shut down.
>
> 2017-02-22 3:45 GMT+08:00 Keith <keith@keithf4.com>:
>
> On Tue, Feb 21, 2017 at 2:33 PM, Ray Stell <stellr@vt.edu> wrote:
>
> On 2/21/17 12:26 PM, Keith wrote:
>
> On Tue, Feb 21, 2017 at 12:22 PM, Ray Stell <stellr@vt.edu> wrote:
>
> On 2/21/17 12:09 AM, Steven Chang wrote:
>
> check this, his 2nd part introduces Stream Replication Implementation and tell you px_log retention and wal archive related parameters.
> https://www.itenlight.com/blog/2016/05/19/PostgreSQL+HA+ with+pgpool-II+-+Part+2
>
> 2017-02-18 2:30 GMT+08:00 Ray Stell <stellr@vt.edu>:
>
> I was "planning" to turn on WAL archiving on a postgresql 9.4.11 server that currently is running with "wal_level=hot_standby" and streaming
> to a standby. I thought there would be a relationship between the rate of pg_xlog files and archive generation. When I turned up the
> archive_command/mode I found the scale of the archive target was wrong as I had based it on the pg_xlog file creation rate.
>
> When I turned on the archive command for a few minutes, pg_xlog dir contained these files for the time period:
>
> -rw------- 1 postgres postgres 16777216 Feb 17 06:47 00000001000023AC0000007F
> -rw------- 1 postgres postgres 16777216 Feb 17 06:45 00000001000023AC0000007E
>
> The archive command wrote 126, 16MB files:
>
> -rw------- 1 postgres postgres 16777216 Feb 17 06:47 000000010000237700000056
> -rw------- 1 postgres postgres 16777216 Feb 17 06:47 000000010000237700000055
> -rw------- 1 postgres postgres 16777216 Feb 17 06:47 000000010000237700000054
> -rw------- 1 postgres postgres 16777216 Feb 17 06:47 000000010000237700000053
> ...
>
> -rw------- 1 postgres postgres 16777216 Feb 17 06:45 0000000100002376000000DC
> -rw------- 1 postgres postgres 16777216 Feb 17 06:45 0000000100002376000000DB
> -rw------- 1 postgres postgres 16777216 Feb 17 06:45 0000000100002376000000DA
> -rw------- 1 postgres postgres 16777216 Feb 17 06:45 0000000100002376000000D9
>
> On servers that are not nearly as busy, I observe a one-to-one relationship between these files/rates.
>
> Is there a good WAL archive space planning guide?
>
> Is the way to collect planning data for this to turn on wal_debug?
>
> TIA!
>
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>
> I'm interested in why I might observed a dramatic difference between pg_xlog files and the archive target files. Other dbs I see have them pretty
> much one-to-one, but not in this case here. What might cause the large variation? I got only a few pg_xlogs files each minute and 42 archive files
> /min.
>
> Ray,
>
> Did you see my previous response about the archive_timeout setting?
>
> Lost your post somehow, but I see it in the list archive. Thanks, Keith.
>
> There was a 30 minute timeout set, but I would not think that would increase the archive file generation as observed, does it?
>
> " When this parameter is greater than zero, the server will switch to a new segment file whenever this many seconds have elapsed since the last segment file
> switch, and there has been any database activity, including a single checkpoint. (Increasing checkpoint_timeout will reduce unnecessary checkpoints on an
> idle system.) "
>
> Your post seems to indicate having a non-zero value might increase the number of archive files, is that so? Maybe it is in milliseconds which might make
> sense with the observed archive rate, but the doc says seconds and it was set to 1800. I can set it to 0 and see if it changes things, but I'm a little
> confused.
>
> If it was set to 30 minutes, then no, it wouldn't explain what you saw. But we didn't know what it was set to, so that's why I asked. Make sure you're checking
> the value actually set in the database, and not just what's in postgresql.conf, since it could've changed but never been reloaded to put in place (type "show
> archive_timeout" in psql).
>
> If that's not it, not sure what may be causing what you're seeing.
>
> Keith
>
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