Limit memory usage of pg_walinspect functions.

jeff-davis · jeff-davis · commit da32a99df1f5 · 2023-02-20T11:29:31.000-08:00
GetWALRecordsInfo() and pg_get_wal_fpi_info() can leak memory across WAL record iterations. Fix this by using a temporary memory context that's reset for each WAL record iteraion. Also use a temporary context for loops in GetXLogSummaryStats(). The number of iterations is a small constant, so the previous behavior was not a leak, but fix for clarity (but no need to backport). Backport GetWALRecordsInfo() change to version 15. pg_get_wal_fpi_info() didn't exist in version 15. Reported-by: Peter Geoghegan Author: Bharath Rupireddy Discussion: https://www.postgresql.org/message-id/CAH2-WznLEJjn7ghmKOABOEZYuJvkTk%3DGKU3m0%2B-XBAH%2BerPiJQ%40mail.gmail.com Backpatch-through: 15
diff --git a/contrib/pg_walinspect/pg_walinspect.c b/contrib/pg_walinspect/pg_walinspect.c
@@ -332,6 +332,8 @@ GetWALRecordsInfo(FunctionCallInfo fcinfo, XLogRecPtr start_lsn,
 	ReturnSetInfo *rsinfo = (ReturnSetInfo *) fcinfo->resultinfo;
 	Datum		values[PG_GET_WAL_RECORDS_INFO_COLS];
 	bool		nulls[PG_GET_WAL_RECORDS_INFO_COLS];
+	MemoryContext old_cxt;
+	MemoryContext tmp_cxt;
 
 	InitMaterializedSRF(fcinfo, 0);
 
@@ -340,18 +342,30 @@ GetWALRecordsInfo(FunctionCallInfo fcinfo, XLogRecPtr start_lsn,
 	MemSet(values, 0, sizeof(values));
 	MemSet(nulls, 0, sizeof(nulls));
 
+	tmp_cxt = AllocSetContextCreate(CurrentMemoryContext,
+									"GetWALRecordsInfo temporary cxt",
+									ALLOCSET_DEFAULT_SIZES);
+
 	while (ReadNextXLogRecord(xlogreader) &&
 		   xlogreader->EndRecPtr <= end_lsn)
 	{
+		/* Use the tmp context so we can clean up after each tuple is done */
+		old_cxt = MemoryContextSwitchTo(tmp_cxt);
+
 		GetWALRecordInfo(xlogreader, values, nulls,
 						 PG_GET_WAL_RECORDS_INFO_COLS);
 
 		tuplestore_putvalues(rsinfo->setResult, rsinfo->setDesc,
 							 values, nulls);
 
+		/* clean up and switch back */
+		MemoryContextSwitchTo(old_cxt);
+		MemoryContextReset(tmp_cxt);
+
 		CHECK_FOR_INTERRUPTS();
 	}
 
+	MemoryContextDelete(tmp_cxt);
 	pfree(xlogreader->private_data);
 	XLogReaderFree(xlogreader);
 
