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Fix up run-time partition pruning's use of relcache's partition data.

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The previous coding saved pointers into the partitioned table's relcache
entry, but then closed the relcache entry, causing those pointers to
nominally become dangling.  Actual trouble would be seen in the field
only if a relcache flush occurred mid-query, but that's hardly out of
the question.

While we could fix this by copying all the data in question at query
start, it seems better to just hold the relcache entry open for the
whole query.

While at it, improve the handling of support-function lookups: do that
once per query not once per pruning test.  There's still something to be
desired here, in that we fail to exploit the possibility of caching data
across queries in the fn_extra fields of the relcache's FmgrInfo structs,
which could happen if we just used those structs in-place rather than
copying them.  However, combining that with the possibility of per-query
lookups of cross-type comparison functions seems to require changes in the
APIs of a lot of the pruning support functions, so it's too invasive to
consider as part of this patch.  A win would ensue only for complex
partition key data types (e.g. arrays), so it may not be worth the
trouble.

David Rowley and Tom Lane

Discussion: https://postgr.es/m/17850.1528755844@sss.pgh.pa.us
This commit is contained in:
Tom Lane
2018-06-13 12:03:19 -04:00
parent e146e4d02d
commit e23bae82cf
6 changed files with 132 additions and 73 deletions
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6
src/backend/utils/cache/relcache.c vendored
View File

@ -2471,6 +2471,7 @@ RelationClearRelation(Relation relation, bool rebuild)
keep_tupdesc = equalTupleDescs(relation->rd_att, newrel->rd_att);
keep_rules = equalRuleLocks(relation->rd_rules, newrel->rd_rules);
keep_policies = equalRSDesc(relation->rd_rsdesc, newrel->rd_rsdesc);
/* partkey is immutable once set up, so we can always keep it */
keep_partkey = (relation->rd_partkey != NULL);
keep_partdesc = equalPartitionDescs(relation->rd_partkey,
relation->rd_partdesc,
@ -2515,7 +2516,7 @@ RelationClearRelation(Relation relation, bool rebuild)
SWAPFIELD(Form_pg_class, rd_rel);
/* ... but actually, we don't have to update newrel->rd_rel */
memcpy(relation->rd_rel, newrel->rd_rel, CLASS_TUPLE_SIZE);
/* preserve old tupledesc and rules if no logical change */
/* preserve old tupledesc, rules, policies if no logical change */
if (keep_tupdesc)
SWAPFIELD(TupleDesc, rd_att);
if (keep_rules)
@ -2529,13 +2530,12 @@ RelationClearRelation(Relation relation, bool rebuild)
SWAPFIELD(Oid, rd_toastoid);
/* pgstat_info must be preserved */
SWAPFIELD(struct PgStat_TableStatus *, pgstat_info);
/* partition key must be preserved, if we have one */
/* preserve old partitioning info if no logical change */
if (keep_partkey)
{
SWAPFIELD(PartitionKey, rd_partkey);
SWAPFIELD(MemoryContext, rd_partkeycxt);
}
/* preserve old partdesc if no logical change */
if (keep_partdesc)
{
SWAPFIELD(PartitionDesc, rd_partdesc);