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 307c6a4ab57366f8e5803c8b389f96f2a1037f4b..e4d21a402fbbe469438c36330fb14b2f1063bbf4 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_itupdesc in case it's an index-only scan */
        so->indexTupDesc = scan->xs_itupdesc = 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 cb8fa9c0b51ea1750a2bc9c16a7ac02a25b7e610..e788a7761f46edb2f6411ebfb2dc84ceeb783c5d 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 */