Horton

Re: [HACKERS] Restricting maximum keep segments by repslots

Alvaro Herrera <alvherre@2ndquadrant.com>

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From: Alvaro Herrera <alvherre@2ndquadrant.com>
To: Kyotaro Horiguchi <horikyota.ntt@gmail.com>
Cc: jgdr@dalibo.com, andres@anarazel.de, michael@paquier.xyz, sawada.mshk@gmail.com, peter.eisentraut@2ndquadrant.com, pgsql-hackers@lists.postgresql.org, thomas.munro@enterprisedb.com, sk@zsrv.org, michael.paquier@gmail.com
Date: 2020-03-31T19:59:05Z
Lists: pgsql-hackers

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On 2020-Mar-31, Alvaro Herrera wrote:

> On 2020-Mar-31, Alvaro Herrera wrote:
> 
> > I'm not sure if I explained my proposal clearly.  What if
> > XLogGetLastRemovedSegno returning zero means that every segment is
> > valid?  We don't need to scan pg_xlog at all.
> 
> I mean this:

[v21 does it that way.  Your typo fixes are included, but not the
LastRemoved stuff being discussed here.  I also edited the shortdesc in
guc.c to better match {min,max}_wal_size.]

Hmm ... but if the user runs pg_resetwal to remove WAL segments, then
this will work badly for a time (until a segment is removed next).  I'm
not very worried for that scenario, since surely the user will have to
reclone any standbys anyway.  I think your v20 behaves better in that
case.  But I'm not sure we should have that code to cater only to that
case ... seems to me that it will go untested 99.999% of the time.

Maybe you're aware of some other cases where lastRemovedSegNo is not
correct for the purposes of this feature?

I pushed the silly test_decoding test adjustment to get it out of the
way.

/me tries to figure out KeepLogSeg next

-- 
Álvaro Herrera                https://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services

Commits

  1. Save slot's restart_lsn when invalidated due to size

  2. Fix checkpoint signalling

  3. Check slot->restart_lsn validity in a few more places

  4. Allow users to limit storage reserved by replication slots

  5. Remove header noise from test_decoding test

  6. Rework WAL-reading supporting structs

  7. Flip argument order in XLogSegNoOffsetToRecPtr