Re: pgsql: Allow users to limit storage reserved by replication slots - Mailing list pgsql-hackers

From Alvaro Herrera
Subject Re: pgsql: Allow users to limit storage reserved by replication slots
Date
Msg-id 20200407232602.GA21559@alvherre.pgsql
Whole thread Raw
Responses Re: pgsql: Allow users to limit storage reserved by replication slots  (Tom Lane <tgl@sss.pgh.pa.us>)
Re: pgsql: Allow users to limit storage reserved by replication slots  (Tom Lane <tgl@sss.pgh.pa.us>)
List pgsql-hackers
On 2020-Apr-07, Alvaro Herrera wrote:

> src/test/recovery/t/019_replslot_limit.pl      | 217 +++++++++++++++++++++++++

I fixed the perlcritic complaint from buildfarm member crake, but
there's a new one in francolin:

#   Failed test 'check that the slot state changes to "reserved"'
#   at t/019_replslot_limit.pl line 125.
#          got: '0/15000D8|reserved|216 bytes'
#     expected: '0/1500000|reserved|216 bytes'

#   Failed test 'check that the slot state changes to "lost"'
#   at t/019_replslot_limit.pl line 135.
#          got: '0/15000D8|lost|t'
#     expected: '0/1500000|lost|t'
# Looks like you failed 2 tests of 13.
[23:07:28] t/019_replslot_limit.pl .............. 

where the Perl code is:

  $start_lsn = $node_master->lsn('write');
  $node_master->wait_for_catchup($node_standby, 'replay', $start_lsn);
  $node_standby->stop;

  # Advance WAL again without checkpoint, reducing remain by 6 MB.
  advance_wal($node_master, 6);

  # Slot gets into 'reserved' state
  $result = $node_master->safe_psql('postgres', "SELECT restart_lsn, wal_status, pg_size_pretty(restart_lsn -
min_safe_lsn)as remain FROM pg_replication_slots WHERE slot_name = 'rep1'");
 
  is($result, "$start_lsn|reserved|216 bytes", 'check that the slot state changes to "reserved"');

0xD8 is 216, so this seems to be saying that the checkpoint record was
skipped by the restart_lsn.  I'm not clear exactly why that happened ...
is this saying that a checkpoint occurred?

One easy fix would be to remove the "restart_lsn" output column from the
query, but do we lose test specificity?  (I think the answer is no.)

However, even with that change, we're still testing that a checkpoint is
216 bytes ... in other words, whenever someone changes the definition of
struct CheckPoint, this test will fail.  That seems unnecessary and
unfriendly.  I'm not sure how to improve that without also removing that
column.

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



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