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Prevent memory leaks associated with relcache rd_partcheck structures.

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The original coding of generate_partition_qual() just copied the list
of predicate expressions into the global CacheMemoryContext, making it
effectively impossible to clean up when the owning relcache entry is
destroyed --- the relevant code in RelationDestroyRelation() only managed
to free the topmost List header :-(.  This resulted in a session-lifespan
memory leak whenever a table partition's relcache entry is rebuilt.
Fortunately, that's not normally a large data structure, and rebuilds
shouldn't occur all that often in production situations; but this is
still a bug worth fixing back to v10 where the code was introduced.

To fix, put the cached expression tree into its own small memory context,
as we do with other complicated substructures of relcache entries.
Also, deal more honestly with the case that a partition has an empty
partcheck list; while that probably isn't a case that's very interesting
for production use, it's legal.

In passing, clarify comments about how partitioning-related relcache
data structures are managed, and add some Asserts that we're not leaking
old copies when we overwrite these data fields.

Amit Langote and Tom Lane

Discussion: https://postgr.es/m/7961.1552498252@sss.pgh.pa.us
This commit is contained in:
Tom Lane
2019-04-13 13:22:26 -04:00
parent 7ef2b313e6
commit 089e4d405d
3 changed files with 80 additions and 30 deletions
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8
src/include/utils/rel.h
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@@ -95,9 +95,9 @@ typedef struct RelationData
List *rd_fkeylist; /* list of ForeignKeyCacheInfo (see below) */
bool rd_fkeyvalid; /* true if list has been computed */
MemoryContext rd_partkeycxt; /* private memory cxt for the below */
MemoryContext rd_partkeycxt; /* private context for rd_partkey, if any */
struct PartitionKeyData *rd_partkey; /* partition key, or NULL */
MemoryContext rd_pdcxt; /* private context for partdesc */
MemoryContext rd_pdcxt; /* private context for rd_partdesc, if any */
struct PartitionDescData *rd_partdesc; /* partitions, or NULL */
List *rd_partcheck; /* partition CHECK quals */
@@ -188,6 +188,10 @@ typedef struct RelationData
/* use "struct" here to avoid needing to include pgstat.h: */
struct PgStat_TableStatus *pgstat_info; /* statistics collection area */
/* placed here to avoid ABI break before v12: */
bool rd_partcheckvalid; /* true if list has been computed */
MemoryContext rd_partcheckcxt; /* private cxt for rd_partcheck, if any */
} RelationData;