Create memory context for HashAgg with a reasonable maxBlockSize.

If the memory context's maxBlockSize is too big, a single block
allocation can suddenly exceed work_mem. For Hash Aggregation, this
can mean spilling to disk too early or reporting a confusing memory
usage number for EXPLAN ANALYZE.

Introduce CreateWorkExprContext(), which is like CreateExprContext(),
except that it creates the AllocSet with a maxBlockSize that is
reasonable in proportion to work_mem.

Right now, CreateWorkExprContext() is only used by Hash Aggregation,
but it may be generally useful in the future.

Discussion: https://postgr.es/m/[email protected]

1 files changed, 1 insertions, 0 deletions

diff --git a/src/include/executor/executor.h b/src/include/executor/executor.h
index 94890512dc8..c7deeac662f 100644
--- a/src/include/executor/executor.h
+++ b/src/include/executor/executor.h
@@ -493,6 +493,7 @@ extern void end_tup_output(TupOutputState *tstate);
 extern EState *CreateExecutorState(void);
 extern void FreeExecutorState(EState *estate);
 extern ExprContext *CreateExprContext(EState *estate);
+extern ExprContext *CreateWorkExprContext(EState *estate);
 extern ExprContext *CreateStandaloneExprContext(void);
 extern void FreeExprContext(ExprContext *econtext, bool isCommit);
 extern void ReScanExprContext(ExprContext *econtext);