AW: [Extern] Re: consistent postgresql snapshot

I don't want to do use the normal backup algorithm where pg_start_backup + pg_stop_backup will fix any fractured block and I am required to have all archived logfiles, therefore.

I want to produce an atomic consistent disk snapshot.

I am not sure if freeze/unfreeze will be enough with default values (8k db blocksize vs. 4k fs blocksize).

I am quite sure it should be safe when I also change the fs blocksize to 8k because 1 IO = 1 db block = 1 fs block than.

Any thoughts?

Von: Ron <ronljohnsonjr(at)gmail(dot)com>
Gesendet: Donnerstag, 12. Mai 2022 01:51
An: pgsql-general(at)lists(dot)postgresql(dot)org
Betreff: [Extern] Re: consistent postgresql snapshot

On 5/11/22 10:41, Zwettler Markus (OIZ) wrote:

PostgreSQL12 running on CentOS7 + ext4.

Would it be save to do a "fsfreeze –freeze" + disk snapshot + "fsfreeze –unfreeze" of the PGDATA filesystem to get a consistent snapshot?

I am wondering as PostgreSQL default blocksize = 8k while ext4 default blocksize = 4k, resulting in 2 fs blocks per db block.

If data/base and pg_xlog are on the same filesystem, then it might work.

Be sure to select pg_start_backup('something informative'); beforehand, and select pg_stop_backup(); afterwards.

For example:
psql -c "select pg_start_backup('something informative');"
fsfreeze –freeze
disk snapshot
fsfreeze –unfreeze
psql -c "select pg_stop_backup();"
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