Make the overflow guards in ExecChooseHashTableSize be more protective.

The original coding ensured nbuckets and nbatch didn't exceed INT_MAX,
which while not insane on its own terms did nothing to protect subsequent
code like "palloc(nbatch * sizeof(BufFile *))".  Since enormous join size
estimates might well be planner error rather than reality, it seems best
to constrain the initial sizes to be not more than work_mem/sizeof(pointer),
thus ensuring the allocated arrays don't exceed work_mem.  We will allow
nbatch to get bigger than that during subsequent ExecHashIncreaseNumBatches
calls, but we should still guard against integer overflow in those palloc
requests.  Per bug #5145 from Bernt Marius Johnsen.

Although the given test case only seems to fail back to 8.2, previous
releases have variants of this issue, so patch all supported branches.

diff --git a/src/backend/executor/nodeHash.c b/src/backend/executor/nodeHash.c
index 2e6a77d89241baf03818e8833cdc96f784d17952..16b84d0f5ad3392ddd3f6738dac61a683ce45fb1 100644 (file)
--- a/src/backend/executor/nodeHash.c
+++ b/src/backend/executor/nodeHash.c
@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *   $PostgreSQL: pgsql/src/backend/executor/nodeHash.c,v 1.122 2009/09/27 21:10:53 tgl Exp $
+ *   $PostgreSQL: pgsql/src/backend/executor/nodeHash.c,v 1.123 2009/10/30 20:58:45 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -394,6 +394,7 @@ ExecChooseHashTableSize(double ntuples, int tupwidth, bool useskew,
    double      inner_rel_bytes;
    long        hash_table_bytes;
    long        skew_table_bytes;
+   long        max_pointers;
    int         nbatch;
    int         nbuckets;
    int         i;
@@ -435,17 +436,18 @@ ExecChooseHashTableSize(double ntuples, int tupwidth, bool useskew,
    {
        skew_table_bytes = hash_table_bytes * SKEW_WORK_MEM_PERCENT / 100;
 
-       *num_skew_mcvs = skew_table_bytes / (
-       /* size of a hash tuple */
-                                            tupsize +
-       /* worst-case size of skewBucket[] per MCV */
+       /*----------
+        * Divisor is:
+        * size of a hash tuple +
+        * worst-case size of skewBucket[] per MCV +
+        * size of skewBucketNums[] entry +
+        * size of skew bucket struct itself
+        *----------
+        */
+       *num_skew_mcvs = skew_table_bytes / (tupsize +
                                             (8 * sizeof(HashSkewBucket *)) +
-       /* size of skewBucketNums[] entry */
                                             sizeof(int) +
-       /* size of skew bucket struct itself */
-                                            SKEW_BUCKET_OVERHEAD
-           );
-
+                                            SKEW_BUCKET_OVERHEAD);
        if (*num_skew_mcvs > 0)
            hash_table_bytes -= skew_table_bytes;
    }
@@ -455,8 +457,13 @@ ExecChooseHashTableSize(double ntuples, int tupwidth, bool useskew,
    /*
     * Set nbuckets to achieve an average bucket load of NTUP_PER_BUCKET when
     * memory is filled.  Set nbatch to the smallest power of 2 that appears
-    * sufficient.
+    * sufficient.  The Min() steps limit the results so that the pointer
+    * arrays we'll try to allocate do not exceed work_mem.
     */
+   max_pointers = (work_mem * 1024L) / sizeof(void *);
+   /* also ensure we avoid integer overflow in nbatch and nbuckets */
+   max_pointers = Min(max_pointers, INT_MAX / 2);
+
    if (inner_rel_bytes > hash_table_bytes)
    {
        /* We'll need multiple batches */
@@ -465,11 +472,11 @@ ExecChooseHashTableSize(double ntuples, int tupwidth, bool useskew,
        int         minbatch;
 
        lbuckets = (hash_table_bytes / tupsize) / NTUP_PER_BUCKET;
-       lbuckets = Min(lbuckets, INT_MAX / 2);
+       lbuckets = Min(lbuckets, max_pointers);
        nbuckets = (int) lbuckets;
 
        dbatch = ceil(inner_rel_bytes / hash_table_bytes);
-       dbatch = Min(dbatch, INT_MAX / 2);
+       dbatch = Min(dbatch, max_pointers);
        minbatch = (int) dbatch;
        nbatch = 2;
        while (nbatch < minbatch)
@@ -481,7 +488,7 @@ ExecChooseHashTableSize(double ntuples, int tupwidth, bool useskew,
        double      dbuckets;
 
        dbuckets = ceil(ntuples / NTUP_PER_BUCKET);
-       dbuckets = Min(dbuckets, INT_MAX / 2);
+       dbuckets = Min(dbuckets, max_pointers);
        nbuckets = (int) dbuckets;
 
        nbatch = 1;
@@ -555,7 +562,7 @@ ExecHashIncreaseNumBatches(HashJoinTable hashtable)
        return;
 
    /* safety check to avoid overflow */
-   if (oldnbatch > INT_MAX / 2)
+   if (oldnbatch > Min(INT_MAX / 2, MaxAllocSize / (sizeof(void *) * 2)))
        return;
 
    nbatch = oldnbatch * 2;
@@ -1033,9 +1040,9 @@ ExecHashBuildSkewHash(HashJoinTable hashtable, Hash *node, int mcvsToUse)
         * will be at least one null entry, so searches will always
         * terminate.)
         *
-        * Note: this code could fail if mcvsToUse exceeds INT_MAX/8, but that
-        * is not currently possible since we limit pg_statistic entries to
-        * much less than that.
+        * Note: this code could fail if mcvsToUse exceeds INT_MAX/8 or
+        * MaxAllocSize/sizeof(void *)/8, but that is not currently possible
+        * since we limit pg_statistic entries to much less than that.
         */
        nbuckets = 2;
        while (nbuckets <= mcvsToUse)