Limit memory usage of pg_walinspect functions.

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 a use 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
index 91b740ed27771231f7a741db636cbc9030255236..b7b0a805ee8477d7233a75f0a6ff4b309e31c46e 100644 (file)
--- a/contrib/pg_walinspect/pg_walinspect.c
+++ b/contrib/pg_walinspect/pg_walinspect.c
@@ -304,6 +304,8 @@ pg_get_wal_fpi_info(PG_FUNCTION_ARGS)
    XLogRecPtr  start_lsn;
    XLogRecPtr  end_lsn;
    XLogReaderState *xlogreader;
+   MemoryContext old_cxt;
+   MemoryContext tmp_cxt;
 
    start_lsn = PG_GETARG_LSN(0);
    end_lsn = PG_GETARG_LSN(1);
@@ -314,14 +316,26 @@ pg_get_wal_fpi_info(PG_FUNCTION_ARGS)
 
    xlogreader = InitXLogReaderState(start_lsn);
 
+   tmp_cxt = AllocSetContextCreate(CurrentMemoryContext,
+                                   "pg_get_wal_fpi_info 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);
+
        GetWALFPIInfo(fcinfo, xlogreader);
 
+       /* clean up and switch back */
+       MemoryContextSwitchTo(old_cxt);
+       MemoryContextReset(tmp_cxt);
+
        CHECK_FOR_INTERRUPTS();
    }
 
+   MemoryContextDelete(tmp_cxt);
    pfree(xlogreader->private_data);
    XLogReaderFree(xlogreader);
 
@@ -440,23 +454,37 @@ GetWALRecordsInfo(FunctionCallInfo fcinfo, XLogRecPtr start_lsn,
    ReturnSetInfo *rsinfo = (ReturnSetInfo *) fcinfo->resultinfo;
    Datum       values[PG_GET_WAL_RECORDS_INFO_COLS] = {0};
    bool        nulls[PG_GET_WAL_RECORDS_INFO_COLS] = {0};
+   MemoryContext old_cxt;
+   MemoryContext tmp_cxt;
 
    InitMaterializedSRF(fcinfo, 0);
 
    xlogreader = InitXLogReaderState(start_lsn);
 
+   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);
 
@@ -560,11 +588,13 @@ GetXLogSummaryStats(XLogStats *stats, ReturnSetInfo *rsinfo,
                    Datum *values, bool *nulls, uint32 ncols,
                    bool stats_per_record)
 {
-   uint64      total_count = 0;
-   uint64      total_rec_len = 0;
-   uint64      total_fpi_len = 0;
-   uint64      total_len = 0;
-   int         ri;
+   MemoryContext   old_cxt;
+   MemoryContext   tmp_cxt;
+   uint64          total_count   = 0;
+   uint64          total_rec_len = 0;
+   uint64          total_fpi_len = 0;
+   uint64          total_len     = 0;
+   int             ri;
 
    /*
     * Each row shows its percentages of the total, so make a first pass to
@@ -581,6 +611,10 @@ GetXLogSummaryStats(XLogStats *stats, ReturnSetInfo *rsinfo,
    }
    total_len = total_rec_len + total_fpi_len;
 
+   tmp_cxt = AllocSetContextCreate(CurrentMemoryContext,
+                                   "GetXLogSummaryStats temporary cxt",
+                                   ALLOCSET_DEFAULT_SIZES);
+
    for (ri = 0; ri <= RM_MAX_ID; ri++)
    {
        uint64      count;
@@ -614,6 +648,8 @@ GetXLogSummaryStats(XLogStats *stats, ReturnSetInfo *rsinfo,
                if (count == 0)
                    continue;
 
+               old_cxt = MemoryContextSwitchTo(tmp_cxt);
+
                /* the upper four bits in xl_info are the rmgr's */
                id = desc.rm_identify(rj << 4);
                if (id == NULL)
@@ -626,6 +662,10 @@ GetXLogSummaryStats(XLogStats *stats, ReturnSetInfo *rsinfo,
 
                tuplestore_putvalues(rsinfo->setResult, rsinfo->setDesc,
                                     values, nulls);
+
+               /* clean up and switch back */
+               MemoryContextSwitchTo(old_cxt);
+               MemoryContextReset(tmp_cxt);
            }
        }
        else
@@ -635,14 +675,22 @@ GetXLogSummaryStats(XLogStats *stats, ReturnSetInfo *rsinfo,
            fpi_len = stats->rmgr_stats[ri].fpi_len;
            tot_len = rec_len + fpi_len;
 
+           old_cxt = MemoryContextSwitchTo(tmp_cxt);
+
            FillXLogStatsRow(desc.rm_name, count, total_count, rec_len,
                             total_rec_len, fpi_len, total_fpi_len, tot_len,
                             total_len, values, nulls, ncols);
 
            tuplestore_putvalues(rsinfo->setResult, rsinfo->setDesc,
                                 values, nulls);
+
+           /* clean up and switch back */
+           MemoryContextSwitchTo(old_cxt);
+           MemoryContextReset(tmp_cxt);
        }
    }
+
+   MemoryContextDelete(tmp_cxt);
 }
 
 /*