AW: [Extern] Re: consistent postgresql snapshot

["Zwettler Markus (OIZ)" <Markus.Zwettler@xxxxxxxxxx>]

Title: Email Signature

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@xxxxxxxxx>
Gesendet: Donnerstag, 12. Mai 2022 01:51
An: pgsql-general@xxxxxxxxxxxxxxxxxxxx
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();"

--
Angular momentum makes the world go 'round.

Achtung: Diese E-Mail wurde von einer externen Adresse verschickt. Klicken Sie auf keine Links und öffnen Sie keine angehängten Dateien, wenn Sie den Absender bzw. die Absenderin nicht kennen. Sind Sie sich unsicher, kontaktieren Sie den Service Desk der Stadt Zürich.