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Fix the incorrect assertion introduced in commit 7f13ac8123.

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It has been incorrectly assumed in commit 7f13ac8123 that we can either
purge all or none in the catalog modifying xids list retrieved from a
serialized snapshot. It is quite possible that some of the xids in that
array are old enough to be pruned but not others.

As per buildfarm

Author: Amit Kapila and Masahiko Sawada
Reviwed-by: Masahiko Sawada
Discussion: https://postgr.es/m/CAA4eK1LBtv6ayE+TvCcPmC-xse=DVg=SmbyQD1nv_AaqcpUJEg@mail.gmail.com
This commit is contained in:
Amit Kapila 2022-08-29 08:10:10 +05:30
parent 8c7fc86ca9
commit d2169c9985
3 changed files with 106 additions and 20 deletions
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56
contrib/test_decoding/expected/catalog_change_snapshot.out
View File

@ -1,4 +1,4 @@
Parsed test spec with 2 sessions
Parsed test spec with 3 sessions
starting permutation: s0_init s0_begin s0_savepoint s0_truncate s1_checkpoint s1_get_changes s0_commit s0_begin s0_insert s1_checkpoint s1_get_changes s0_commit s1_get_changes
step s0_init: SELECT 'init' FROM pg_create_logical_replication_slot('isolation_slot', 'test_decoding');
@ -42,3 +42,57 @@ COMMIT
stop
(1 row)
starting permutation: s0_init s0_begin s0_truncate s2_begin s2_truncate s1_checkpoint s1_get_changes s0_commit s0_begin s0_insert s1_checkpoint s1_get_changes s2_commit s1_checkpoint s1_get_changes s0_commit s1_get_changes
step s0_init: SELECT 'init' FROM pg_create_logical_replication_slot('isolation_slot', 'test_decoding');
?column?
--------
init
(1 row)
step s0_begin: BEGIN;
step s0_truncate: TRUNCATE tbl1;
step s2_begin: BEGIN;
step s2_truncate: TRUNCATE tbl2;
step s1_checkpoint: CHECKPOINT;
step s1_get_changes: SELECT data FROM pg_logical_slot_get_changes('isolation_slot', NULL, NULL, 'skip-empty-xacts', '1', 'include-xids', '0');
data
----
(0 rows)
step s0_commit: COMMIT;
step s0_begin: BEGIN;
step s0_insert: INSERT INTO tbl1 VALUES (1);
step s1_checkpoint: CHECKPOINT;
step s1_get_changes: SELECT data FROM pg_logical_slot_get_changes('isolation_slot', NULL, NULL, 'skip-empty-xacts', '1', 'include-xids', '0');
data
---------------------------------------
BEGIN
table public.tbl1: TRUNCATE: (no-flags)
COMMIT
(3 rows)
step s2_commit: COMMIT;
step s1_checkpoint: CHECKPOINT;
step s1_get_changes: SELECT data FROM pg_logical_slot_get_changes('isolation_slot', NULL, NULL, 'skip-empty-xacts', '1', 'include-xids', '0');
data
---------------------------------------
BEGIN
table public.tbl2: TRUNCATE: (no-flags)
COMMIT
(3 rows)
step s0_commit: COMMIT;
step s1_get_changes: SELECT data FROM pg_logical_slot_get_changes('isolation_slot', NULL, NULL, 'skip-empty-xacts', '1', 'include-xids', '0');
data
-------------------------------------------------------------
BEGIN
table public.tbl1: INSERT: val1[integer]:1 val2[integer]:null
COMMIT
(3 rows)
?column?
--------
stop
(1 row)

20
contrib/test_decoding/specs/catalog_change_snapshot.spec
View File

@ -3,12 +3,15 @@
setup
{
DROP TABLE IF EXISTS tbl1;
DROP TABLE IF EXISTS tbl2;
CREATE TABLE tbl1 (val1 integer, val2 integer);
CREATE TABLE tbl2 (val1 integer, val2 integer);
}
teardown
{
DROP TABLE tbl1;
DROP TABLE tbl2;
SELECT 'stop' FROM pg_drop_replication_slot('isolation_slot');
}
@ -26,6 +29,12 @@ setup { SET synchronous_commit=on; }
step "s1_checkpoint" { CHECKPOINT; }
step "s1_get_changes" { SELECT data FROM pg_logical_slot_get_changes('isolation_slot', NULL, NULL, 'skip-empty-xacts', '1', 'include-xids', '0'); }
session "s2"
setup { SET synchronous_commit=on; }
step "s2_begin" { BEGIN; }
step "s2_truncate" { TRUNCATE tbl2; }
step "s2_commit" { COMMIT; }
# For the transaction that TRUNCATEd the table tbl1, the last decoding decodes
# only its COMMIT record, because it starts from the RUNNING_XACTS record emitted
# during the first checkpoint execution. This transaction must be marked as
@ -37,3 +46,14 @@ step "s1_get_changes" { SELECT data FROM pg_logical_slot_get_changes('isolation_
# record written by bgwriter. One might think we can either stop the bgwriter or
# increase LOG_SNAPSHOT_INTERVAL_MS but it's not practical via tests.
permutation "s0_init" "s0_begin" "s0_savepoint" "s0_truncate" "s1_checkpoint" "s1_get_changes" "s0_commit" "s0_begin" "s0_insert" "s1_checkpoint" "s1_get_changes" "s0_commit" "s1_get_changes"
# Test that we can purge the old catalog modifying transactions after restoring
# them from the serialized snapshot. The first checkpoint will serialize the list
# of two catalog modifying xacts. The purpose of the second checkpoint is to allow
# partial pruning of the list of catalog modifying xact. The third checkpoint
# followed by get_changes establishes a restart_point at the first checkpoint LSN.
# The last get_changes will start decoding from the first checkpoint which
# restores the list of catalog modifying xacts and then while decoding the second
# checkpoint record it prunes one of the xacts in that list and when decoding the
# next checkpoint, it will completely prune that list.
permutation "s0_init" "s0_begin" "s0_truncate" "s2_begin" "s2_truncate" "s1_checkpoint" "s1_get_changes" "s0_commit" "s0_begin" "s0_insert" "s1_checkpoint" "s1_get_changes" "s2_commit" "s1_checkpoint" "s1_get_changes" "s0_commit" "s1_get_changes"

50
src/backend/replication/logical/snapbuild.c
View File

@ -969,28 +969,40 @@ SnapBuildPurgeOlderTxn(SnapBuild *builder)
pfree(workspace);
/*
* Either all the xacts got purged or none. It is only possible to
* partially remove the xids from this array if one or more of the xids
* are still running but not all. That can happen if we start decoding
* from a point (LSN where the snapshot state became consistent) where all
* the xacts in this were running and then at least one of those got
* committed and a few are still running. We will never start from such a
* point because we won't move the slot's restart_lsn past the point where
* the oldest running transaction's restart_decoding_lsn is.
* Purge xids in ->catchange as well. The purged array must also be sorted
* in xidComparator order.
*/
if (builder->catchange.xcnt == 0 ||
TransactionIdFollowsOrEquals(builder->catchange.xip[0],
builder->xmin))
return;
if (builder->catchange.xcnt > 0)
{
/*
* Since catchange.xip is sorted, we find the lower bound of xids that
* are still interesting.
*/
for (off = 0; off < builder->catchange.xcnt; off++)
{
if (TransactionIdFollowsOrEquals(builder->catchange.xip[off],
builder->xmin))
break;
}
Assert(TransactionIdFollows(builder->xmin,
builder->catchange.xip[builder->catchange.xcnt - 1]));
pfree(builder->catchange.xip);
builder->catchange.xip = NULL;
builder->catchange.xcnt = 0;
surviving_xids = builder->catchange.xcnt - off;
elog(DEBUG3, "purged catalog modifying transactions, oldest running xid %u",
builder->xmin);
if (surviving_xids > 0)
{
memmove(builder->catchange.xip, &(builder->catchange.xip[off]),
surviving_xids * sizeof(TransactionId));
}
else
{
pfree(builder->catchange.xip);
builder->catchange.xip = NULL;
}
elog(DEBUG3, "purged catalog modifying transactions from %u to %u, xmin: %u, xmax: %u",
(uint32) builder->catchange.xcnt, (uint32) surviving_xids,
builder->xmin, builder->xmax);
builder->catchange.xcnt = surviving_xids;
}
}
/*