Fix handling of all-zero pages in SP-GiST vacuum.

SP-GiST initialized an all-zeros page at vacuum, but that was not
WAL-logged, which is not safe. You might get a torn page write, when it gets
flushed to disk, and end-up with a half-initialized index page. To fix,
leave it in the all-zeros state, and add it to the FSM. It will be
initialized when reused. Also don't set the page-deleted flag when recycling
an empty page. That was also not WAL-logged, and a torn write of that would
cause the page to have an invalid checksum.

Backpatch to 9.2, where SP-GiST indexes were added.

diff --git a/src/backend/access/spgist/spgvacuum.c b/src/backend/access/spgist/spgvacuum.c
index dc69d1ed20fccae53547d100e003a57c284f1e3c..d40da0eeccad20596f2082c94089965c9004df29 100644 (file)
--- a/src/backend/access/spgist/spgvacuum.c
+++ b/src/backend/access/spgist/spgvacuum.c
@@ -621,14 +621,10 @@ spgvacuumpage(spgBulkDeleteState *bds, BlockNumber blkno)
        {
                /*
                 * We found an all-zero page, which could happen if the database
-                * crashed just after extending the file.  Initialize and recycle it.
+                * crashed just after extending the file.  Recycle it.
                 */
-               SpGistInitBuffer(buffer, 0);
-               SpGistPageSetDeleted(page);
-               /* We don't bother to WAL-log this action; easy to redo */
-               MarkBufferDirty(buffer);
        }
-       else if (SpGistPageIsDeleted(page))
+       else if (PageIsEmpty(page))
        {
                /* nothing to do */
        }
@@ -654,30 +650,23 @@ spgvacuumpage(spgBulkDeleteState *bds, BlockNumber blkno)
        /*
         * The root pages must never be deleted, nor marked as available in FSM,
         * because we don't want them ever returned by a search for a place to put
-        * a new tuple.  Otherwise, check for empty/deletable page, and make sure
-        * FSM knows about it.
+        * a new tuple.  Otherwise, check for empty page, and make sure the FSM
+        * knows about it.
         */
        if (!SpGistBlockIsRoot(blkno))
        {
-               /* If page is now empty, mark it deleted */
-               if (PageIsEmpty(page) && !SpGistPageIsDeleted(page))
-               {
-                       SpGistPageSetDeleted(page);
-                       /* We don't bother to WAL-log this action; easy to redo */
-                       MarkBufferDirty(buffer);
-               }
-
-               if (SpGistPageIsDeleted(page))
+               if (PageIsEmpty(page))
                {
                        RecordFreeIndexPage(index, blkno);
                        bds->stats->pages_deleted++;
                }
                else
+               {
+                       SpGistSetLastUsedPage(index, buffer);
                        bds->lastFilledBlock = blkno;
+               }
        }
 
-       SpGistSetLastUsedPage(index, buffer);
-
        UnlockReleaseBuffer(buffer);
 }
 

diff --git a/src/include/access/spgist_private.h b/src/include/access/spgist_private.h
index 413f71e7298d3835b6ba4f673528d51832d70ff4..48dadd5b2c6c7571c0a987fa6a49006ffecd737e 100644 (file)
--- a/src/include/access/spgist_private.h
+++ b/src/include/access/spgist_private.h
@@ -48,14 +48,14 @@ typedef SpGistPageOpaqueData *SpGistPageOpaque;
 
 /* Flag bits in page special space */
 #define SPGIST_META                    (1<<0)
-#define SPGIST_DELETED         (1<<1)
+#define SPGIST_DELETED         (1<<1)          /* never set, but keep for backwards
+                                                                                * compatibility */
 #define SPGIST_LEAF                    (1<<2)
 #define SPGIST_NULLS           (1<<3)
 
 #define SpGistPageGetOpaque(page) ((SpGistPageOpaque) PageGetSpecialPointer(page))
 #define SpGistPageIsMeta(page) (SpGistPageGetOpaque(page)->flags & SPGIST_META)
 #define SpGistPageIsDeleted(page) (SpGistPageGetOpaque(page)->flags & SPGIST_DELETED)
-#define SpGistPageSetDeleted(page) (SpGistPageGetOpaque(page)->flags |= SPGIST_DELETED)
 #define SpGistPageIsLeaf(page) (SpGistPageGetOpaque(page)->flags & SPGIST_LEAF)
 #define SpGistPageStoresNulls(page) (SpGistPageGetOpaque(page)->flags & SPGIST_NULLS)