Обсуждение: Different Autovacuum Settings on Master and Replica in Streaming Replication
Different Autovacuum Settings on Master and Replica in Streaming Replication
Question regarding autovacuum settings in a PostgreSQL streaming replication setup. Specifically, I am curious about whether it is possible (and advisable) to have different values for the following settings on the master and replica databases:
- autovacuum_vacuum_scale_factor
- autovacuum_analyze_scale_factor
Can the above settings be configured differently on the master and replica databases in a streaming replication setup? I just tested this on AWS RDS Postgres.
How would those different settings interact with replication, for example, if I apply change on master, would it be replicated to replica and override my replica setting?
I was expecting that this is not possible in streaming replication, only in logical replication.
Thank you!
Franjo Stipanovic <fritzfs@gmail.com> writes:
> Question regarding autovacuum settings in a PostgreSQL streaming
> replication setup. Specifically, I am curious about whether it is possible
> (and advisable) to have different values for the following settings on the
> master and replica databases:
> - autovacuum_vacuum_scale_factor
> - autovacuum_analyze_scale_factor
A streaming replica will not run vacuum on its own, as it just absorbs
the physical changes made by vacuum on the master. Hence, it matters
not at all how you have those values set on the replica.
If the replica is promoted to master, then it will start to use
whatever settings it has (and no, postgresql.conf is not copied
by the replication infrastructure).
regards, tom lane
Re: Different Autovacuum Settings on Master and Replica in Streaming Replication
Question regarding autovacuum settings in a PostgreSQL streaming replication setup. Specifically, I am curious about whether it is possible (and advisable) to have different values for the following settings on the master and replica databases:
- autovacuum_vacuum_scale_factor
- autovacuum_analyze_scale_factorCan the above settings be configured differently on the master and replica databases in a streaming replication setup? I just tested this on AWS RDS Postgres.
How would those different settings interact with replication, for example, if I apply change on master, would it be replicated to replica and override my replica setting?
I was expecting that this is not possible in streaming replication, only in logical replication.
Re: Different Autovacuum Settings on Master and Replica in Streaming Replication
Hi,--Le ven. 17 janv. 2025 à 15:38, Franjo Stipanovic <fritzfs@gmail.com> a écrit :Question regarding autovacuum settings in a PostgreSQL streaming replication setup. Specifically, I am curious about whether it is possible (and advisable) to have different values for the following settings on the master and replica databases:
- autovacuum_vacuum_scale_factor
- autovacuum_analyze_scale_factorCan the above settings be configured differently on the master and replica databases in a streaming replication setup? I just tested this on AWS RDS Postgres.
They could but it doesn't matter. VACUUM and ANALYZE aren't executed on replicas because they are write operations, and you can't write on replicas.How would those different settings interact with replication, for example, if I apply change on master, would it be replicated to replica and override my replica setting?
Changes on the postgresq.conf file aren't replicated, but ALTER TABLE ... (SET autovacuum...) are.I was expecting that this is not possible in streaming replication, only in logical replication.
You're right, it's not possible.Guillaume.
Franjo Stipanovic
Re: Different Autovacuum Settings on Master and Replica in Streaming Replication
Thank you, Guillaume, Tom.In that case, querying pg_stat_user_tables on replica for last_vacuum, last_autovacuum, last_analyze, and last_autoanalyze columns makes no sense? Those specific columns are not transferred from the master? The same goes for n_* columns? Currently, on my replica, all those columns are null and 0, while on the master they have a value.
Seems like only seq_scan, last_seq_scan, idx_scan, ... are fulfilled.
Also, data behind pg_stats (n_distinct, most_common_vals, most_common_freqs, etc) is replicated, right? It seems that we can query those just fine.
On Fri, Jan 17, 2025 at 4:34 PM Guillaume Lelarge <guillaume@lelarge.info> wrote:Hi,--Le ven. 17 janv. 2025 à 15:38, Franjo Stipanovic <fritzfs@gmail.com> a écrit :Question regarding autovacuum settings in a PostgreSQL streaming replication setup. Specifically, I am curious about whether it is possible (and advisable) to have different values for the following settings on the master and replica databases:
- autovacuum_vacuum_scale_factor
- autovacuum_analyze_scale_factorCan the above settings be configured differently on the master and replica databases in a streaming replication setup? I just tested this on AWS RDS Postgres.
They could but it doesn't matter. VACUUM and ANALYZE aren't executed on replicas because they are write operations, and you can't write on replicas.How would those different settings interact with replication, for example, if I apply change on master, would it be replicated to replica and override my replica setting?
Changes on the postgresq.conf file aren't replicated, but ALTER TABLE ... (SET autovacuum...) are.I was expecting that this is not possible in streaming replication, only in logical replication.
You're right, it's not possible.Guillaume.--best wishes,
Franjo Stipanovic
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