Fix GiST index-only scans for opclasses with different storage type.

We cannot use the index's tuple descriptor directly to describe the index
tuples returned in an index-only scan. That's because the index might use
a different datatype for the values stored on disk than the type originally
indexed. As long as they were both pass-by-ref, it worked, but will not work
for pass-by-value types of different sizes. I noticed this as a crash when I
started hacking a patch to add fetch methods to btree_gist.

diff --git a/src/backend/access/gist/gistscan.c b/src/backend/access/gist/gistscan.c
index 3522d75a49674ff05f9ffefc6e192556da892efe..6f6539823026052b2690469c373ee564898fa2a8 100644 (file)
--- a/src/backend/access/gist/gistscan.c
+++ b/src/backend/access/gist/gistscan.c
@@ -89,11 +89,9 @@ gistbeginscan(PG_FUNCTION_ARGS)
    scan->opaque = so;
 
    /*
-    * All fields required for index-only scans are null until gistrescan.
-    * However, we set up scan->xs_itupdesc whether we'll need it or not,
-    * since that's cheap.
+    * All fields required for index-only scans are initialized in gistrescan,
+    * as we don't know yet if we're doing an index-only scan or not.
     */
-   scan->xs_itupdesc = RelationGetDescr(r);
 
    MemoryContextSwitchTo(oldCxt);
 
@@ -149,15 +147,37 @@ gistrescan(PG_FUNCTION_ARGS)
    }
 
    /*
-    * If we're doing an index-only scan, also create a memory context to hold
-    * the returned tuples.
+    * If we're doing an index-only scan, on the first call, also initialize
+    * a tuple descriptor to represent the returned index tuples and create a
+    * memory context to hold them during the scan.
     */
-   if (scan->xs_want_itup && so->pageDataCxt == NULL)
+   if (scan->xs_want_itup && !scan->xs_itupdesc)
+   {
+       int         natts;
+       int         attno;
+
+       /*
+        * The storage type of the index can be different from the original
+        * datatype being indexed, so we cannot just grab the index's tuple
+        * descriptor. Instead, construct a descriptor with the original data
+        * types.
+        */
+       natts =  RelationGetNumberOfAttributes(scan->indexRelation);
+       so->giststate->fetchTupdesc = CreateTemplateTupleDesc(natts, false);
+       for (attno = 1; attno <= natts; attno++)
+       {
+           TupleDescInitEntry(so->giststate->fetchTupdesc, attno, NULL,
+                              scan->indexRelation->rd_opcintype[attno - 1],
+                              -1, 0);
+       }
+       scan->xs_itupdesc = so->giststate->fetchTupdesc;
+
        so->pageDataCxt = AllocSetContextCreate(so->giststate->scanCxt,
                                                "GiST page data context",
                                                ALLOCSET_DEFAULT_MINSIZE,
                                                ALLOCSET_DEFAULT_INITSIZE,
                                                ALLOCSET_DEFAULT_MAXSIZE);
+   }
 
    /* create new, empty RBTree for search queue */
    oldCxt = MemoryContextSwitchTo(so->queueCxt);

diff --git a/src/backend/access/gist/gistutil.c b/src/backend/access/gist/gistutil.c
index 1680251a18b647998e8aeab9c507b71b62220a8a..bf9fbf30a8b0f30d970acefbf79b722ba15a8c31 100644 (file)
--- a/src/backend/access/gist/gistutil.c
+++ b/src/backend/access/gist/gistutil.c
@@ -657,7 +657,7 @@ gistFetchTuple(GISTSTATE *giststate, Relation r, IndexTuple tuple)
    }
    MemoryContextSwitchTo(oldcxt);
 
-   return index_form_tuple(giststate->tupdesc, fetchatt, isnull);
+   return index_form_tuple(giststate->fetchTupdesc, fetchatt, isnull);
 }
 
 float

diff --git a/src/include/access/gist_private.h b/src/include/access/gist_private.h
index 3693893e261dde172cb690d2262342a8ca312ca2..9d3714d27d207e22c552b4035849ceb5d53c9ddb 100644 (file)
--- a/src/include/access/gist_private.h
+++ b/src/include/access/gist_private.h
@@ -78,6 +78,8 @@ typedef struct GISTSTATE
    MemoryContext tempCxt;      /* short-term context for calling functions */
 
    TupleDesc   tupdesc;        /* index's tuple descriptor */
+   TupleDesc   fetchTupdesc;   /* tuple descriptor for tuples returned in an
+                                * index-only scan */
 
    FmgrInfo    consistentFn[INDEX_MAX_KEYS];
    FmgrInfo    unionFn[INDEX_MAX_KEYS];