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authorTom Lane2018-01-03 02:23:02 +0000
committerTom Lane2018-01-03 02:23:06 +0000
commit5dc692f78d3bee1e86d095a9e8d9242b44f78b01 (patch)
tree76ba4d6b57529e606988d9939851ea97793757c4 /src/include
parent54eff5311d7c8e3d309774713b91e78067d2ad42 (diff)
Ensure proper alignment of tuples in HashMemoryChunkData buffers.
The previous coding relied (without any documentation) on the data[] member of HashMemoryChunkData being at a MAXALIGN'ed offset. If it was not, the tuples would not be maxaligned either, leading to failures on alignment-picky machines. While there seems to be no live bug on any platform we support, this is clearly pretty fragile: any addition to or rearrangement of the fields in HashMemoryChunkData could break it. Let's remove the hazard by getting rid of the data[] member and instead using pointer arithmetic with an explicitly maxalign'ed offset. Discussion: https://postgr.es/m/14483.1514938129@sss.pgh.pa.us
Diffstat (limited to 'src/include')
-rw-r--r--src/include/executor/hashjoin.h12
1 files changed, 9 insertions, 3 deletions
diff --git a/src/include/executor/hashjoin.h b/src/include/executor/hashjoin.h
index d8c82d4e7c0..be83500b9df 100644
--- a/src/include/executor/hashjoin.h
+++ b/src/include/executor/hashjoin.h
@@ -117,7 +117,7 @@ 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) */
@@ -127,13 +127,19 @@ typedef struct HashMemoryChunkData
dsa_pointer 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)
/*