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Commit5561404

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Avoid query-lifetime memory leaks in XMLTABLE (bug #15321)
Multiple calls to XMLTABLE in a query (e.g. laterally applying it to atable with an xml column, an important use-case) were leaking largeamounts of memory into the per-query context, blowing up memory usage.Repair by reorganizing memory context usage in nodeTableFuncscan; usethe usual per-tuple context for row-by-row evaluations instead ofperValueCxt, and use the explicitly created context -- renamed fromperValueCxt to perTableCxt -- for arguments and state for eachindividual table-generation operation.Backpatch to PG10 where this code was introduced.Original report by IRC user begriffs; analysis and patch by me.Reviewed by Tom Lane and Pavel Stehule.Discussion:https://postgr.es/m/153394403528.10284.7530399040974170549@wrigleys.postgresql.org
1 parent26853a8 commit5561404

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2 files changed

+25
-6
lines changed

2 files changed

+25
-6
lines changed

‎src/backend/executor/nodeTableFuncscan.c

Lines changed: 24 additions & 5 deletions
Original file line numberDiff line numberDiff line change
@@ -170,7 +170,7 @@ ExecInitTableFuncScan(TableFuncScan *node, EState *estate, int eflags)
170170
/* Only XMLTABLE is supported currently */
171171
scanstate->routine=&XmlTableRoutine;
172172

173-
scanstate->perValueCxt=
173+
scanstate->perTableCxt=
174174
AllocSetContextCreate(CurrentMemoryContext,
175175
"TableFunc per value context",
176176
ALLOCSET_DEFAULT_SIZES);
@@ -288,6 +288,16 @@ tfuncFetchRows(TableFuncScanState *tstate, ExprContext *econtext)
288288
oldcxt=MemoryContextSwitchTo(econtext->ecxt_per_query_memory);
289289
tstate->tupstore=tuplestore_begin_heap(false, false,work_mem);
290290

291+
/*
292+
* Each call to fetch a new set of rows - of which there may be very many
293+
* if XMLTABLE is being used in a lateral join - will allocate a possibly
294+
* substantial amount of memory, so we cannot use the per-query context
295+
* here. perTableCxt now serves the same function as "argcontext" does in
296+
* FunctionScan - a place to store per-one-call (i.e. one result table)
297+
* lifetime data (as opposed to per-query or per-result-tuple).
298+
*/
299+
MemoryContextSwitchTo(tstate->perTableCxt);
300+
291301
PG_TRY();
292302
{
293303
routine->InitOpaque(tstate,
@@ -319,15 +329,17 @@ tfuncFetchRows(TableFuncScanState *tstate, ExprContext *econtext)
319329
}
320330
PG_END_TRY();
321331

322-
/* return to original memory context, and clean up */
323-
MemoryContextSwitchTo(oldcxt);
332+
/* clean up and return to original memory context */
324333

325334
if (tstate->opaque!=NULL)
326335
{
327336
routine->DestroyOpaque(tstate);
328337
tstate->opaque=NULL;
329338
}
330339

340+
MemoryContextSwitchTo(oldcxt);
341+
MemoryContextReset(tstate->perTableCxt);
342+
331343
return;
332344
}
333345

@@ -433,7 +445,14 @@ tfuncLoadRows(TableFuncScanState *tstate, ExprContext *econtext)
433445

434446
ordinalitycol=
435447
((TableFuncScan*) (tstate->ss.ps.plan))->tablefunc->ordinalitycol;
436-
oldcxt=MemoryContextSwitchTo(tstate->perValueCxt);
448+
449+
/*
450+
* We need a short-lived memory context that we can clean up each time
451+
* around the loop, to avoid wasting space. Our default per-tuple context
452+
* is fine for the job, since we won't have used it for anything yet in
453+
* this tuple cycle.
454+
*/
455+
oldcxt=MemoryContextSwitchTo(econtext->ecxt_per_tuple_memory);
437456

438457
/*
439458
* Keep requesting rows from the table builder until there aren't any.
@@ -496,7 +515,7 @@ tfuncLoadRows(TableFuncScanState *tstate, ExprContext *econtext)
496515

497516
tuplestore_putvalues(tstate->tupstore,tupdesc,values,nulls);
498517

499-
MemoryContextReset(tstate->perValueCxt);
518+
MemoryContextReset(econtext->ecxt_per_tuple_memory);
500519
}
501520

502521
MemoryContextSwitchTo(oldcxt);

‎src/include/nodes/execnodes.h

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -1484,7 +1484,7 @@ typedef struct TableFuncScanState
14841484
FmgrInfo*in_functions;/* input function for each column */
14851485
Oid*typioparams;/* typioparam for each column */
14861486
int64ordinal;/* row number to be output next */
1487-
MemoryContextperValueCxt;/*short lifecontext for value evaluation */
1487+
MemoryContextperTableCxt;/*per-tablecontext */
14881488
Tuplestorestate*tupstore;/* output tuple store */
14891489
}TableFuncScanState;
14901490

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