Обсуждение: Need help to make space on my database

On 4/29/24 06:45, Cocam' server wrote:
> Hello.
> 
> I need help to make space on my database. I have tables that are several 
> GB in size. I used to use the VACUUM FULL VERBOSE command; but now, this 
> command is too greedy in free space to be used and I'm looking for a way 
> to make free space (given back to the OS)
> 
> Thanks in advance to everyone who responds

Per

https://www.postgresql.org/docs/current/sql-vacuum.html

"VACUUM reclaims storage occupied by dead tuples. In normal PostgreSQL 
operation, tuples that are deleted or obsoleted by an update are not 
physically removed from their table; they remain present until a VACUUM 
is done. Therefore it's necessary to do VACUUM periodically, especially 
on frequently-updated tables.

<...>

Plain VACUUM (without FULL) simply reclaims space and makes it available 
for re-use. This form of the command can operate in parallel with normal 
reading and writing of the table, as an exclusive lock is not obtained. 
However, extra space is not returned to the operating system (in most 
cases); it's just kept available for re-use within the same table.
"

So a regular VACUUM should work if all you want to do is give the 
database the ability to recycle the vacuumed tuple space.

-- 
Adrian Klaver
adrian.klaver@aklaver.com

On 4/29/24 07:33, Cocam' server wrote:

Please reply to list also
Ccing list

> No, the aim is also to reallocate free space to the system for the other 
> tasks it performs.(That's why I said I'd like it returned to the OS)

You led with:

"I need help to make space on my database".

How much current free space do you have available on the disk?

Did you VACUUM FULL a table at a time or all of them at once?

What are the individual tables sizes?

> 
> Le lun. 29 avr. 2024 à 16:19, Adrian Klaver <adrian.klaver@aklaver.com 
> <mailto:adrian.klaver@aklaver.com>> a écrit :
> 
>     On 4/29/24 06:45, Cocam' server wrote:
>      > Hello.
>      >
>      > I need help to make space on my database. I have tables that are
>     several
>      > GB in size. I used to use the VACUUM FULL VERBOSE command; but
>     now, this
>      > command is too greedy in free space to be used and I'm looking
>     for a way
>      > to make free space (given back to the OS)
>      >
>      > Thanks in advance to everyone who responds
> 
>     Per
> 
>     https://www.postgresql.org/docs/current/sql-vacuum.html
>     <https://www.postgresql.org/docs/current/sql-vacuum.html>
> 
>     "VACUUM reclaims storage occupied by dead tuples. In normal PostgreSQL
>     operation, tuples that are deleted or obsoleted by an update are not
>     physically removed from their table; they remain present until a VACUUM
>     is done. Therefore it's necessary to do VACUUM periodically, especially
>     on frequently-updated tables.
> 
>     <...>
> 
>     Plain VACUUM (without FULL) simply reclaims space and makes it
>     available
>     for re-use. This form of the command can operate in parallel with
>     normal
>     reading and writing of the table, as an exclusive lock is not obtained.
>     However, extra space is not returned to the operating system (in most
>     cases); it's just kept available for re-use within the same table.
>     "
> 
>     So a regular VACUUM should work if all you want to do is give the
>     database the ability to recycle the vacuumed tuple space.
> 
>     -- 
>     Adrian Klaver
>     adrian.klaver@aklaver.com <mailto:adrian.klaver@aklaver.com>
> 

-- 
Adrian Klaver
adrian.klaver@aklaver.com

On 4/29/24 08:04, Cocam' server wrote:

When replying use Reply All to include the mailing list
Ccing list

>  > How much current free space do you have available on the disk?
> as we speak, I only have 6 GB available on the machine running the server
> 
>  > Did you VACUUM FULL a table at a time or all of them at once?
> I tried to make a VACUUM FULL. I also tried on the biggest tables (200 
> Mb and +) but not on all of them

Did the above work for each table?

Have you done something like?:

select relname, n_dead_tup from pg_stat_all_tables where relname = 
'<table_name>';

to see if there any dead tuples to clean out.

Or if you use the contrib extension pgstattuple:

https://www.postgresql.org/docs/current/pgstattuple.html

then:

SELECT * FROM pgstattuple('<table_name>');

This returns something like:

-[ RECORD 1 ]------+--------
table_len          | 3940352
tuple_count        | 4310
tuple_len          | 3755414
tuple_percent      | 95.31
dead_tuple_count   | 0
dead_tuple_len     | 0
dead_tuple_percent | 0
free_space         | 124060
free_percent       | 3.15


> 
> The two biggest are these:
>   state_groups_state | 5475 MB
>   event_json | 2328 MB
> 
> (I'd particularly like to make room on these two tables, which take up 
> the most space)
> 
> By the way, excuse me if I make a few mistakes (especially when 
> replying), this is the first time I've used Postgres community support 
> directly
> 
> 
> Le lun. 29 avr. 2024 à 16:37, Adrian Klaver <adrian.klaver@aklaver.com 
> <mailto:adrian.klaver@aklaver.com>> a écrit :
> 
>     On 4/29/24 07:33, Cocam' server wrote:
> 
>     Please reply to list also
>     Ccing list
> 
>      > No, the aim is also to reallocate free space to the system for
>     the other
>      > tasks it performs.(That's why I said I'd like it returned to the OS)
> 
>     You led with:
> 
>     "I need help to make space on my database".
> 
>     How much current free space do you have available on the disk?
> 
>     Did you VACUUM FULL a table at a time or all of them at once?
> 
>     What are the individual tables sizes?
> 
>      >
>      > Le lun. 29 avr. 2024 à 16:19, Adrian Klaver
>     <adrian.klaver@aklaver.com <mailto:adrian.klaver@aklaver.com>
>      > <mailto:adrian.klaver@aklaver.com
>     <mailto:adrian.klaver@aklaver.com>>> a écrit :
>      >
>      >     On 4/29/24 06:45, Cocam' server wrote:
>      >      > Hello.
>      >      >
>      >      > I need help to make space on my database. I have tables
>     that are
>      >     several
>      >      > GB in size. I used to use the VACUUM FULL VERBOSE command; but
>      >     now, this
>      >      > command is too greedy in free space to be used and I'm looking
>      >     for a way
>      >      > to make free space (given back to the OS)
>      >      >
>      >      > Thanks in advance to everyone who responds
>      >
>      >     Per
>      >
>      > https://www.postgresql.org/docs/current/sql-vacuum.html
>     <https://www.postgresql.org/docs/current/sql-vacuum.html>
>      >     <https://www.postgresql.org/docs/current/sql-vacuum.html
>     <https://www.postgresql.org/docs/current/sql-vacuum.html>>
>      >
>      >     "VACUUM reclaims storage occupied by dead tuples. In normal
>     PostgreSQL
>      >     operation, tuples that are deleted or obsoleted by an update
>     are not
>      >     physically removed from their table; they remain present
>     until a VACUUM
>      >     is done. Therefore it's necessary to do VACUUM periodically,
>     especially
>      >     on frequently-updated tables.
>      >
>      >     <...>
>      >
>      >     Plain VACUUM (without FULL) simply reclaims space and makes it
>      >     available
>      >     for re-use. This form of the command can operate in parallel with
>      >     normal
>      >     reading and writing of the table, as an exclusive lock is not
>     obtained.
>      >     However, extra space is not returned to the operating system
>     (in most
>      >     cases); it's just kept available for re-use within the same
>     table.
>      >     "
>      >
>      >     So a regular VACUUM should work if all you want to do is give the
>      >     database the ability to recycle the vacuumed tuple space.
>      >
>      >     --
>      >     Adrian Klaver
>      > adrian.klaver@aklaver.com <mailto:adrian.klaver@aklaver.com>
>     <mailto:adrian.klaver@aklaver.com <mailto:adrian.klaver@aklaver.com>>
>      >
> 
>     -- 
>     Adrian Klaver
>     adrian.klaver@aklaver.com <mailto:adrian.klaver@aklaver.com>
> 

-- 
Adrian Klaver
adrian.klaver@aklaver.com

On Mon, 2024-04-29 at 15:45 +0200, Cocam' server wrote:
> I need help to make space on my database. I have tables that are several GB in size.
> I used to use the VACUUM FULL VERBOSE command; but now, this command is too greedy in
> free space to be used and I'm looking for a way to make free space (given back to the OS)

If you don't have enough disk space for a VACUUM (FULL), your only option is
pg_dump / DROP DATABASE / CREATE DATABASE / restore.

Yours,
Laurenz Albe

On 4/29/24 08:51, Cocam' server wrote:
>  > Did the above work for each table?
> Yes, except for the biggest table
> 
>  > Have you done something like?:
>  >
>  > select relname, n_dead_tup from pg_stat_all_tables where relname =
>  > '<table_name>';
> 
> I hadn't thought of that, but it seems that some tables have dead tuples
> 

You have something against providing actual numbers?

The point is there is really nothing to be gained by doing VACUUM FULL 
if the dead tuples are some small percentage of the tables.

-- 
Adrian Klaver
adrian.klaver@aklaver.com