Ensure proper alignment of tuples in HashMemoryChunkData buffers

pg commitid  5dc692f78d3

src/gausskernel/runtime/executor/nodeHash.cpp

@@ -1126,7 +1126,7 @@ static void ExecHashIncreaseNumBatches(HashJoinTable hashtable)
 
         /* process all tuples stored in this chunk (and then free it) */
         while (idx < oldchunks->used) {
-            HashJoinTuple hashTuple = (HashJoinTuple)(oldchunks->data + idx);
+            HashJoinTuple hashTuple = (HashJoinTuple)(HASH_CHUNK_DATA(oldchunks) + idx);
             MinimalTuple tuple = HJTUPLE_MINTUPLE(hashTuple);
             int hashTupleSize = (HJTUPLE_OVERHEAD + tuple->t_len);
             int bucketno;
@@ -1402,7 +1402,7 @@ static void ExecParallelHashRepartitionFirst(HashJoinTable hashtable)
 
         /* Repartition all tuples in this chunk. */
         while (idx < chunk->used) {
-            HashJoinTuple hashTuple = (HashJoinTuple)(chunk->data + idx);
+            HashJoinTuple hashTuple = (HashJoinTuple)(HASH_CHUNK_DATA(chunk) + idx);
             MinimalTuple tuple = HJTUPLE_MINTUPLE(hashTuple);
             HashJoinTuple copyTuple;
             HashJoinTuple shared;
@@ -1571,7 +1571,7 @@ static void ExecParallelHashIncreaseNumBuckets(HashJoinTable hashtable)
             while ((chunk = ExecParallelHashPopChunkQueue(hashtable, &chunk_s))) {
                 size_t idx = 0;
                 while (idx < chunk->used) {
-                    HashJoinTuple hashTuple = (HashJoinTuple)(chunk->data + idx);
+                    HashJoinTuple hashTuple = (HashJoinTuple)(HASH_CHUNK_DATA(chunk) + idx);
                     int bucketno;
                     int batchno;
 
@@ -2714,10 +2714,10 @@ static void* dense_alloc(HashJoinTable hashtable, Size size)
      */
     if (size > HASH_CHUNK_THRESHOLD) {
         /* allocate new chunk and put it at the beginning of the list */
-        newChunk = (HashMemoryChunk)MemoryContextAlloc(hashtable->batchCxt, offsetof(HashMemoryChunkData, data) + size);
+        newChunk = (HashMemoryChunk)MemoryContextAlloc(hashtable->batchCxt, HASH_CHUNK_HEADER_SIZE + size);
         newChunk->maxlen = size;
-        newChunk->used = 0;
-        newChunk->ntuples = 0;
+        newChunk->used = size;
+        newChunk->ntuples = 1;
 
         /*
          * Add this chunk to the list after the first existing chunk, so that
@@ -2731,10 +2731,7 @@ static void* dense_alloc(HashJoinTable hashtable, Size size)
             hashtable->chunks = newChunk;
         }
 
-        newChunk->used += size;
-        newChunk->ntuples += 1;
-
-        return newChunk->data;
+        return HASH_CHUNK_DATA(newChunk);
     }
 
     /*
@@ -2743,8 +2740,7 @@ static void* dense_alloc(HashJoinTable hashtable, Size size)
      */
     if ((hashtable->chunks == NULL) || (hashtable->chunks->maxlen - hashtable->chunks->used) < size) {
         /* allocate new chunk and put it at the beginning of the list */
-        newChunk = (HashMemoryChunk)MemoryContextAlloc(
-            hashtable->batchCxt, offsetof(HashMemoryChunkData, data) + HASH_CHUNK_SIZE);
+        newChunk = (HashMemoryChunk)MemoryContextAlloc(hashtable->batchCxt, HASH_CHUNK_HEADER_SIZE + HASH_CHUNK_SIZE);
 
         newChunk->maxlen = HASH_CHUNK_SIZE;
         newChunk->used = size;
@@ -2753,11 +2749,11 @@ static void* dense_alloc(HashJoinTable hashtable, Size size)
         newChunk->next.unshared = hashtable->chunks;
         hashtable->chunks = newChunk;
 
-        return newChunk->data;
+        return HASH_CHUNK_DATA(newChunk);
     }
 
     /* There is enough space in the current chunk, let's add the tuple */
-    ptr = hashtable->chunks->data + hashtable->chunks->used;
+    ptr = HASH_CHUNK_DATA(hashtable->chunks) + hashtable->chunks->used;
     hashtable->chunks->used += size;
     hashtable->chunks->ntuples += 1;
 
@@ -2794,7 +2790,7 @@ static HashJoinTuple ExecParallelHashTupleAlloc(HashJoinTable hashtable, size_t
     if (chunk != NULL && size < HASH_CHUNK_THRESHOLD && chunk->maxlen - chunk->used >= size) {
         chunk_shared = (HashMemoryChunk)hashtable->current_chunk_shared;
         Assert(chunk == dsa_get_address(hashtable->area, chunk_shared));
-        HashJoinTuple result = (HashJoinTuple)(chunk->data + chunk->used);
+        HashJoinTuple result = (HashJoinTuple)(HASH_CHUNK_DATA(chunk) + chunk->used);
         *shared = result;
         chunk->used += size;
         Assert(chunk->used <= chunk->maxlen);
@@ -2873,7 +2869,7 @@ static HashJoinTuple ExecParallelHashTupleAlloc(HashJoinTable hashtable, size_t
     chunk_shared = chunk_shared;
     chunk_shared->maxlen = chunk_size - HASH_CHUNK_HEADER_SIZE;
     chunk_shared->used = size;
-    *shared = (HashJoinTuple)chunk_shared->data;
+    *shared = (HashJoinTuple)HASH_CHUNK_DATA(chunk_shared);
 
     /*
      * Push it onto the list of chunks, so that it can be found if we need to
@@ -2892,8 +2888,8 @@ static HashJoinTuple ExecParallelHashTupleAlloc(HashJoinTable hashtable, size_t
         hashtable->current_chunk_shared = chunk_shared;
     }
     LWLockRelease(&pstate->lock);
-    Assert(chunk_shared->data == (void*)dsa_get_address(hashtable->area, *shared));
-    return (HashJoinTuple)chunk_shared->data;
+    Assert(HASH_CHUNK_DATA(chunk_shared) == (void*)dsa_get_address(hashtable->area, *shared));
+    return (HashJoinTuple)HASH_CHUNK_DATA(chunk_shared);
 }
 
 /*

src/include/executor/hashjoin.h

@@ -114,7 +114,7 @@ typedef struct HashSkewBucket {
  */
 typedef struct HashMemoryChunkData {
     int ntuples;   /* number of tuples stored in this chunk */
-    size_t maxlen; /* size of the buffer holding the tuples */
+    size_t maxlen; /* size of the chunk's tuple buffer */
     size_t used;   /* number of buffer bytes already used */
 
     /* pointer to the next chunk (linked list) */
@@ -122,13 +122,19 @@ typedef struct HashMemoryChunkData {
         HashMemoryChunkData* unshared;
         HashMemoryChunkData* shared;
     } next;
-    char data[FLEXIBLE_ARRAY_MEMBER]; /* buffer allocated at the end */
+    /*
+	 * The chunk's tuple buffer starts after the HashMemoryChunkData struct,
+	 * at offset HASH_CHUNK_HEADER_SIZE (which must be maxaligned).  Note that
+	 * that offset is not included in "maxlen" or "used".
+	 */
 } HashMemoryChunkData;
 
 typedef struct HashMemoryChunkData* HashMemoryChunk;
 
 #define HASH_CHUNK_SIZE (32 * 1024L)
-#define HASH_CHUNK_HEADER_SIZE (offsetof(HashMemoryChunkData, data))
+#define HASH_CHUNK_HEADER_SIZE	MAXALIGN(sizeof(HashMemoryChunkData))
+#define HASH_CHUNK_DATA(hc)		(((char *) (hc)) + HASH_CHUNK_HEADER_SIZE)
+/* tuples exceeding HASH_CHUNK_THRESHOLD bytes are put in their own chunk */
 #define HASH_CHUNK_THRESHOLD (HASH_CHUNK_SIZE / 4)
 
 /*