Re: table bloat very fast and free space can not be reused - Mailing list pgsql-performance
| From | James Pang |
|---|---|
| Subject | Re: table bloat very fast and free space can not be reused |
| Date | |
| Msg-id | CAHgTRff8Z_ntRLg8cAWtdTi47m716T7j0-xfy9c2PsJigcX-WA@mail.gmail.com Whole thread |
| In response to | Re: table bloat very fast and free space can not be reused (Christophe Pettus <xof@thebuild.com>) |
| List | pgsql-performance |
1. we use default fill factor in both source and target, sorry, we have two environment, v14-->v17, v16-->v17. both see similar issue.
2. any key difference between in-core and pglogical extension to apply UPDATEs? we want to use pglogical extension conflict resolution, it's a bi-directional replication(when workload on source v16 it replicate data to v17, when it running on v17, so it can replication back to v16)
3. free space is high in source and target, but the size of freespace show big difference
we found this issue , and try to vacuum full several time on v17, but after vacuum full , it bloating very quickly.you see total toast size
much more than source (workload is still running), target v17(by pglogical)
xxx=> select * from pgstattuple('xxxx');
table_len | tuple_count | tuple_len | tuple_percent | dead_tuple_count | dead_tuple_len | dead_tuple_percent | free_space | free_percent
-----------+-------------+-----------+---------------+------------------+----------------+--------------------+------------+--------------
191160320 | 81911 | 107823097 | 56.4 | 1439 | 2020471 | 1.06 | 79614944 | 41.65
(1 row)
xxx=> select * from pgstattuple('pg_toast.pg_toast_xxxxx');
table_len | tuple_count | tuple_len | tuple_percent | dead_tuple_count | dead_tuple_len | dead_tuple_percent | free_space | free_percent
-----------+-------------+-----------+---------------+------------------+----------------+--------------------+------------+--------------
905928704 | 117924 | 169760027 | 18.74 | 6330 | 9336459 | 1.03 | 722476480 | 79.75
(1 row)
target v17
xxxx=> select * from pgstattuple('xxxxxx');
table_len | tuple_count | tuple_len | tuple_percent | dead_tuple_count | dead_tuple_len | dead_tuple_percent | free_space | free_percent
-----------+-------------+-----------+---------------+------------------+----------------+--------------------+------------+--------------
194191360 | 81905 | 106028087 | 54.6 | 4004 | 5801923 | 2.99 | 80468096 | 41.44
(1 row)
xxxx=> select * from pgstattuple('pg_toast.pg_toast_xxxxx');
table_len | tuple_count | tuple_len | tuple_percent | dead_tuple_count | dead_tuple_len | dead_tuple_percent | free_space | free_percent
------------+-------------+-----------+---------------+------------------+----------------+--------------------+------------+--------------
1666334720 | 117921 | 169758344 | 10.19 | 9302 | 13732019 | 0.82 | 1475454612 | 88.54
(1 row)
much more than source (workload is still running), target v17(by pglogical)
xxx=> select * from pgstattuple('xxxx');
table_len | tuple_count | tuple_len | tuple_percent | dead_tuple_count | dead_tuple_len | dead_tuple_percent | free_space | free_percent
-----------+-------------+-----------+---------------+------------------+----------------+--------------------+------------+--------------
191160320 | 81911 | 107823097 | 56.4 | 1439 | 2020471 | 1.06 | 79614944 | 41.65
(1 row)
xxx=> select * from pgstattuple('pg_toast.pg_toast_xxxxx');
table_len | tuple_count | tuple_len | tuple_percent | dead_tuple_count | dead_tuple_len | dead_tuple_percent | free_space | free_percent
-----------+-------------+-----------+---------------+------------------+----------------+--------------------+------------+--------------
905928704 | 117924 | 169760027 | 18.74 | 6330 | 9336459 | 1.03 | 722476480 | 79.75
(1 row)
target v17
xxxx=> select * from pgstattuple('xxxxxx');
table_len | tuple_count | tuple_len | tuple_percent | dead_tuple_count | dead_tuple_len | dead_tuple_percent | free_space | free_percent
-----------+-------------+-----------+---------------+------------------+----------------+--------------------+------------+--------------
194191360 | 81905 | 106028087 | 54.6 | 4004 | 5801923 | 2.99 | 80468096 | 41.44
(1 row)
xxxx=> select * from pgstattuple('pg_toast.pg_toast_xxxxx');
table_len | tuple_count | tuple_len | tuple_percent | dead_tuple_count | dead_tuple_len | dead_tuple_percent | free_space | free_percent
------------+-------------+-----------+---------------+------------------+----------------+--------------------+------------+--------------
1666334720 | 117921 | 169758344 | 10.19 | 9302 | 13732019 | 0.82 | 1475454612 | 88.54
(1 row)
James
Christophe Pettus <xof@thebuild.com> 於 2026年4月19日週日 上午11:56寫道：
> On Apr 18, 2026, at 18:28, James Pang <jamespang886@gmail.com> wrote:
>
> experts:
> source database v14 , pglogical extension 2.4.5 replication to new 17, source table very frequent UPDATEs /DELETES /INSERTS and has two text and jsonb. in source database, application update/delete/insert through SQL, table size did not increased quickly. but in target pg v17 , by pglogical apply, we found table increased very quickly , table size got doubled in days.
> Vacuum analyze did not help , only vacuum full can help. pgstattuple show most of space are free space , that much more than source. it looks like these replicate DML always asking new pages instead of reuse existing freespace.
> Thanks,
>
> James
Hello,
1. First, are you *sure* that the free space is the source of the bloat, and not dead tuples? Could you share the queries you ran to detrmine this?
2. Have you set fillfactor to anything besides 100 on either the source or the destination?
3. You might consider using in-core logical replication rather than pglogical for this. By PostgreSQL v14, in-core logical replication is likely a better choice.
Best,
-- Christophe
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