Обсуждение: VACUUM freeze
Hi Arnav,
Could be wrong here, in which case someone will jump in.
My understanding is that freeze only applies while doing the vacuum, and then only when doing a manual vacuum.
I looked at the documentation at https://www.postgresql.org/docs/current/sql-vacuum.html and https://www.postgresql.org/docs/current/routine-vacuuming.html to try to confirm, but did feel a little confused.
Hope this helps a bit.
Dave
From: Arnav [mailto:justdba03@gmail.com]
Sent: 18 April 2020 19:26
To: pgsql-admin
Subject: VACUUM freeze
hi
what is VACUUM freeze , does it not allow autovacuum to happen ever.
if yes till how long?
--
Regards
Arnav
Hi Arnav,
Could be wrong here, in which case someone will jump in.
My understanding is that freeze only applies while doing the vacuum, and then only when doing a manual vacuum.
I looked at the documentation at https://www.postgresql.org/docs/current/sql-vacuum.html and https://www.postgresql.org/docs/current/routine-vacuuming.html to try to confirm, but did feel a little confused.
Hope this helps a bit.
Dave
From: Arnav [mailto:justdba03@gmail.com]
Sent: 18 April 2020 19:26
To: pgsql-admin
Subject: VACUUM freeze
hi
what is VACUUM freeze , does it not allow autovacuum to happen ever.
if yes till how long?
--
Regards
Arnav
Ankush Chawla
> On Apr 19, 2020, at 1:15 AM, Ankush Chawla <ankushchawla03@gmail.com> wrote: > > This will enable for older version to stay. Counting on not vacuuming tables in order to keep old row versions around forever is a really bad idea. What are you tryingto accomplish?
thanks for replyThen what would be way if we want some tables to be skipped for autovacuum.What do you think, what should we do?This will enable for older version to stay.
--On Sun, Apr 19, 2020 at 4:05 AM Dave Bolt <dave@davebolt.co.uk> wrote:Hi Arnav,
Could be wrong here, in which case someone will jump in.
My understanding is that freeze only applies while doing the vacuum, and then only when doing a manual vacuum.
I looked at the documentation at https://www.postgresql.org/docs/current/sql-vacuum.html and https://www.postgresql.org/docs/current/routine-vacuuming.html to try to confirm, but did feel a little confused.
Hope this helps a bit.
Dave
From: Arnav [mailto:justdba03@gmail.com]
Sent: 18 April 2020 19:26
To: pgsql-admin
Subject: VACUUM freeze
hi
what is VACUUM freeze , does it not allow autovacuum to happen ever.
if yes till how long?
--
Regards
Arnav
Best Regards,
Ankush Chawla
Hi Ankush,On Sun, Apr 19, 2020 at 9:16 AM Ankush Chawla <ankushchawla03@gmail.com> wrote:thanks for replyThen what would be way if we want some tables to be skipped for autovacuum.What do you think, what should we do?This will enable for older version to stay.VACUUM FREEZE means that you will put a lock on the table and release it after the job is completed. It is the most effective option but requires a kind of down time for all queries on the table.
If you refer to "older version to stay", you may intend to access deleted data (i.e. when you run an UPDATE, you actually run an INSERT and a DELETE). Deleted data is not accessible. If you need to have access to historical data, I'd suggest creating a history table keeping track of all INSERT, UPDATE and DELETE.If you plan to reduce the impact of the VACUUM in terms of performance and lock-time, I would recommend, on the contrary, to run it often, so that it has a minimal amount of work to do. Disabling vacuum will increase your probability of filling your tables with unnecessary bloat. We evaluated the option of running a vacuum daily on a table with millions of rows and quickly came to the conclusion that it was a really bad idea.
On Sun, Apr 19, 2020 at 4:05 AM Dave Bolt <dave@davebolt.co.uk> wrote:Hi Arnav,
Could be wrong here, in which case someone will jump in.
My understanding is that freeze only applies while doing the vacuum, and then only when doing a manual vacuum.
I looked at the documentation at https://www.postgresql.org/docs/current/sql-vacuum.html and https://www.postgresql.org/docs/current/routine-vacuuming.html to try to confirm, but did feel a little confused.
Hope this helps a bit.
Dave
On Sat, 2020-04-18 at 23:55 +0530, Arnav wrote: > what is VACUUM freeze , does it not allow autovacuum to happen ever. > if yes till how long? VACUUM (FREEZE) marks all rows that are visible to everybody as unconditionally visible. All rows that live long have to get frozen at some point, so that they can survive transaction wraparound without data corruption, because the internal transaction ID that created them is stored in the row metadata. This can be useful for insert-only tables, since autovacuum won't have to touch frozen rows ever again unless they get updated or deleted. The negative aspect of freezing all rows is that all rows that are frozen get modified, which means that the block containing them becomes dirty and has to be written to disk again. Now if any such row is modified or deleted later, freezing the row has generated unnecessary I/O. This is why by default VACUUM will freeze only rows whose creating transaction is more then 50 million transactions in the past, in the hope that such rows have less chance to be modified again than more recent rows. Yours, Laurenz Albe -- Cybertec | https://www.cybertec-postgresql.com