Prevent query-lifespan memory leakage of SP-GiST traversal values.

The original coding of the SP-GiST scan traversalValue feature (commit
ccd6eb49a) arranged for traversal values to be stored in the query's main
executor context.  That's fine if there's only one index scan per query,
but if there are many, we have a memory leak as successive scans create
new traversal values.  Fix it by creating a separate memory context for
traversal values, which we can reset during spgrescan().  Back-patch
to 9.6 where this code was introduced.

In principle, adding the traversalCxt field to SpGistScanOpaqueData
creates an ABI break in the back branches.  But I (tgl) have little
sympathy for extensions including spgist_private.h, so I'm not very
worried about that.  Alternatively we could stick the new field at the
end of the struct in back branches, but that has its own downsides.

Anton Dignös, reviewed by Alexander Kuzmenkov

Discussion: https://postgr.es/m/CALNdv1jb6y2Te-m8xHLxLX12RsBmZJ1f4hESX7J0HjgyOhA9eA@mail.gmail.com

diff --git a/src/backend/access/spgist/spgscan.c b/src/backend/access/spgist/spgscan.c
index 7965b5846d9c85ddd880b55d71366911e87aa32f..adcee037e666f5ffc1e56d42eb9973b704fae15e 100644 (file)
--- a/src/backend/access/spgist/spgscan.c
+++ b/src/backend/access/spgist/spgscan.c
@@ -194,6 +194,9 @@ spgbeginscan(Relation rel, int keysz, int orderbysz)
        so->tempCxt = AllocSetContextCreate(CurrentMemoryContext,
                                                                                "SP-GiST search temporary context",
                                                                                ALLOCSET_DEFAULT_SIZES);
+       so->traversalCxt = AllocSetContextCreate(CurrentMemoryContext,
+                                                                                        "SP-GiST traversal-value context",
+                                                                                        ALLOCSET_DEFAULT_SIZES);
 
        /* Set up indexTupDesc and xs_hitupdesc in case it's an index-only scan */
        so->indexTupDesc = scan->xs_hitupdesc = RelationGetDescr(rel);
@@ -209,6 +212,9 @@ spgrescan(IndexScanDesc scan, ScanKey scankey, int nscankeys,
 {
        SpGistScanOpaque so = (SpGistScanOpaque) scan->opaque;
 
+       /* clear traversal context before proceeding to the next scan */
+       MemoryContextReset(so->traversalCxt);
+
        /* copy scankeys into local storage */
        if (scankey && scan->numberOfKeys > 0)
        {
@@ -229,6 +235,7 @@ spgendscan(IndexScanDesc scan)
        SpGistScanOpaque so = (SpGistScanOpaque) scan->opaque;
 
        MemoryContextDelete(so->tempCxt);
+       MemoryContextDelete(so->traversalCxt);
 }
 
 /*
@@ -463,7 +470,7 @@ redirect:
                        in.scankeys = so->keyData;
                        in.nkeys = so->numberOfKeys;
                        in.reconstructedValue = stackEntry->reconstructedValue;
-                       in.traversalMemoryContext = oldCtx;
+                       in.traversalMemoryContext = so->traversalCxt;
                        in.traversalValue = stackEntry->traversalValue;
                        in.level = stackEntry->level;
                        in.returnData = so->want_itup;

diff --git a/src/include/access/spgist_private.h b/src/include/access/spgist_private.h
index 1c4b321b6c653140690a525c3b6abe88fba47626..cac3f627c80ead7a8b94fb3a55e9e911f189a9c0 100644 (file)
--- a/src/include/access/spgist_private.h
+++ b/src/include/access/spgist_private.h
@@ -136,6 +136,7 @@ typedef struct SpGistScanOpaqueData
 {
        SpGistState state;                      /* see above */
        MemoryContext tempCxt;          /* short-lived memory context */
+       MemoryContext traversalCxt; /* memory context for traversalValues */
 
        /* Control flags showing whether to search nulls and/or non-nulls */
        bool            searchNulls;    /* scan matches (all) null entries */