From: | Robert Haas <robertmhaas(at)gmail(dot)com> |
---|---|
To: | Andres Freund <andres(at)anarazel(dot)de> |
Cc: | David Steele <david(at)pgmasters(dot)net>, Noah Misch <noah(at)leadboat(dot)com>, Stephen Frost <sfrost(at)snowman(dot)net>, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com>, Suraj Kharage <suraj(dot)kharage(at)enterprisedb(dot)com>, tushar <tushar(dot)ahuja(at)enterprisedb(dot)com>, Rajkumar Raghuwanshi <rajkumar(dot)raghuwanshi(at)enterprisedb(dot)com>, Rushabh Lathia <rushabh(dot)lathia(at)gmail(dot)com>, Tels <nospam-pg-abuse(at)bloodgate(dot)com>, Andrew Dunstan <andrew(dot)dunstan(at)2ndquadrant(dot)com>, PostgreSQL Hackers <pgsql-hackers(at)postgresql(dot)org>, Jeevan Chalke <jeevan(dot)chalke(at)enterprisedb(dot)com>, vignesh C <vignesh21(at)gmail(dot)com> |
Subject: | Re: backup manifests |
Date: | 2020-04-02 19:42:48 |
Message-ID: | CA+TgmoaGoQM74CMJhqg3_M7osWgkT2xSxo9aGVu9E4Nt+8Z4sg@mail.gmail.com |
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Lists: | pgsql-hackers |
On Thu, Apr 2, 2020 at 2:55 PM Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
> On Thu, Apr 2, 2020 at 2:23 PM Andres Freund <andres(at)anarazel(dot)de> wrote:
> > > That might make the window fairly wide on normal systems, but I'm not
> > > sure about Raspberry Pi BF members or things running
> > > CLOBBER_CACHE_ALWAYS/RECURSIVELY. I guess I could try it.
> >
> > You can set checkpoint_timeout to be a day. If that's not enough, well,
> > then I think we have other problems.
>
> I'm not sure that's the only issue here, but I'll try it.
I ran into a few problems here. In trying to set this up manually, I
always began with the following steps:
====
# (1) create cluster
initdb
# (2) add to configuration file
log_checkpoints=on
checkpoint_timeout=1d
checkpoint_completion_target=0.99
# (3) fire it up
postgres
createdb
====
If at this point I do "pg_basebackup -D pgslave -R -c spread", it
completes within a few seconds anyway, because there's basically
nothing dirty, and no matter how slowly you write out no data, it's
still pretty quick. If I run "pgbench -i" first, and then
"pg_basebackup -D pgslave -R -c spread", it hangs, apparently
essentially forever, because now the checkpoint has something to do,
and it does it super-slowly, and "psql -c checkpoint" makes it finish
immediately. However, this experiment isn't testing quite the right
thing, because what I actually need is a slow backup off of a
cascading standby, so that I have time to promote the parent standby
before the backup completes. I tried continuing like this:
====
# (4) set up standby
pg_basebackup -D pgslave -R
postgres -D pgslave -c port=5433
# (5) set up cascading standby
pg_basebackup -D pgslave2 -d port=5433 -R
postgres -c port=5434 -D pgslave2
# (6) dirty some pages on the master
pgbench -i
# (7) start a backup of the cascading standby
pg_basebackup -D pgslave3 -d port=5434 -R -c spread
====
However, the pg_basebackup in the last step completes after only a few
seconds. If it were hanging, then I could continue with "pg_ctl
promote -D pgslave" and that might give me what I need, but that's not
what happens.
I suspect I'm not doing quite what you had in mind here... thoughts?
--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company
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