compact_fsm_storage() does need to handle the case where a relation's

FSM data has to be both moved down and compressed.  Per report from
Dror Matalon.

diff --git a/src/backend/storage/freespace/freespace.c b/src/backend/storage/freespace/freespace.c
index a172c4aa48a449c7a5e0d3f55f9bf18be65a7b25..4ce97778ac29d8b3564438387e08a5efd56f1ddd 100644 (file)
--- a/src/backend/storage/freespace/freespace.c
+++ b/src/backend/storage/freespace/freespace.c
@@ -1432,19 +1432,29 @@ compact_fsm_storage(void)
 
                /*
                 * It's possible that we have to move data down, not up, if the
-                * allocations of previous rels expanded.  This should mean that
+                * allocations of previous rels expanded.  This normally means that
                 * our allocation expanded too (or at least got no worse), and
-                * ditto for later rels.  So there should be room --- but we might
-                * have to push down following rels to make it.  We don't want to
-                * do the push more than once, so pack everything against the end
-                * of the arena if so.
+                * ditto for later rels.  So there should be room to move all our
+                * data down without dropping any --- but we might have to push down
+                * following rels to acquire the room.  We don't want to do the push
+                * more than once, so pack everything against the end of the arena
+                * if so.
+                *
+                * In corner cases where roundoff has affected our allocation, it's
+                * possible that we have to move down and compress our data too.
+                * Since this case is extremely infrequent, we do not try to be smart
+                * about it --- we just drop pages from the end of the rel's data.
                 */
                if (newChunkIndex > oldChunkIndex)
                {
                        int                     limitChunkIndex;
 
                        if (newAllocPages < fsmrel->storedPages)
-                               elog(PANIC, "can't juggle and compress too");
+                       {
+                               /* move and compress --- just drop excess pages */
+                               fsmrel->storedPages = newAllocPages;
+                               curChunks = fsm_current_chunks(fsmrel);
+                       }
                        if (fsmrel->nextPhysical != NULL)
                                limitChunkIndex = fsmrel->nextPhysical->firstChunk;
                        else
@@ -1459,7 +1469,7 @@ compact_fsm_storage(void)
                                else
                                        limitChunkIndex = FreeSpaceMap->totalChunks;
                                if (newChunkIndex + curChunks > limitChunkIndex)
-                                       elog(PANIC, "insufficient room");
+                                       elog(PANIC, "insufficient room in FSM");
                        }
                        memmove(newLocation, oldLocation, curChunks * CHUNKBYTES);
                }
@@ -1535,7 +1545,7 @@ push_fsm_rels_after(FSMRelation *afterRel)
                if (newChunkIndex < oldChunkIndex)
                {
                        /* trouble... */
-                       elog(PANIC, "out of room");
+                       elog(PANIC, "insufficient room in FSM");
                }
                else if (newChunkIndex > oldChunkIndex)
                {