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-rw-r--r--src/backend/access/heap/visibilitymap.c68
1 files changed, 68 insertions, 0 deletions
diff --git a/src/backend/access/heap/visibilitymap.c b/src/backend/access/heap/visibilitymap.c
index 5a0511f1988..919e8de0426 100644
--- a/src/backend/access/heap/visibilitymap.c
+++ b/src/backend/access/heap/visibilitymap.c
@@ -16,6 +16,8 @@
* visibilitymap_pin_ok - check whether correct map page is already pinned
* visibilitymap_set - set a bit in a previously pinned page
* visibilitymap_test - test if a bit is set
+ * visibilitymap_count - count number of bits set in visibility map
+ * visibilitymap_truncate - truncate the visibility map
*
* NOTES
*
@@ -110,6 +112,26 @@
#define HEAPBLK_TO_MAPBYTE(x) (((x) % HEAPBLOCKS_PER_PAGE) / HEAPBLOCKS_PER_BYTE)
#define HEAPBLK_TO_MAPBIT(x) ((x) % HEAPBLOCKS_PER_BYTE)
+/* table for fast counting of set bits */
+static const uint8 number_of_ones[256] = {
+ 0, 1, 1, 2, 1, 2, 2, 3, 1, 2, 2, 3, 2, 3, 3, 4,
+ 1, 2, 2, 3, 2, 3, 3, 4, 2, 3, 3, 4, 3, 4, 4, 5,
+ 1, 2, 2, 3, 2, 3, 3, 4, 2, 3, 3, 4, 3, 4, 4, 5,
+ 2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6,
+ 1, 2, 2, 3, 2, 3, 3, 4, 2, 3, 3, 4, 3, 4, 4, 5,
+ 2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6,
+ 2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6,
+ 3, 4, 4, 5, 4, 5, 5, 6, 4, 5, 5, 6, 5, 6, 6, 7,
+ 1, 2, 2, 3, 2, 3, 3, 4, 2, 3, 3, 4, 3, 4, 4, 5,
+ 2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6,
+ 2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6,
+ 3, 4, 4, 5, 4, 5, 5, 6, 4, 5, 5, 6, 5, 6, 6, 7,
+ 2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6,
+ 3, 4, 4, 5, 4, 5, 5, 6, 4, 5, 5, 6, 5, 6, 6, 7,
+ 3, 4, 4, 5, 4, 5, 5, 6, 4, 5, 5, 6, 5, 6, 6, 7,
+ 4, 5, 5, 6, 5, 6, 6, 7, 5, 6, 6, 7, 6, 7, 7, 8
+};
+
/* prototypes for internal routines */
static Buffer vm_readbuf(Relation rel, BlockNumber blkno, bool extend);
static void vm_extend(Relation rel, BlockNumber nvmblocks);
@@ -308,6 +330,52 @@ visibilitymap_test(Relation rel, BlockNumber heapBlk, Buffer *buf)
}
/*
+ * visibilitymap_count - count number of bits set in visibility map
+ *
+ * Note: we ignore the possibility of race conditions when the table is being
+ * extended concurrently with the call. New pages added to the table aren't
+ * going to be marked all-visible, so they won't affect the result.
+ */
+BlockNumber
+visibilitymap_count(Relation rel)
+{
+ BlockNumber result = 0;
+ BlockNumber mapBlock;
+
+ for (mapBlock = 0; ; mapBlock++)
+ {
+ Buffer mapBuffer;
+ unsigned char *map;
+ int i;
+
+ /*
+ * Read till we fall off the end of the map. We assume that any
+ * extra bytes in the last page are zeroed, so we don't bother
+ * excluding them from the count.
+ */
+ mapBuffer = vm_readbuf(rel, mapBlock, false);
+ if (!BufferIsValid(mapBuffer))
+ break;
+
+ /*
+ * We choose not to lock the page, since the result is going to be
+ * immediately stale anyway if anyone is concurrently setting or
+ * clearing bits, and we only really need an approximate value.
+ */
+ map = (unsigned char *) PageGetContents(BufferGetPage(mapBuffer));
+
+ for (i = 0; i < MAPSIZE; i++)
+ {
+ result += number_of_ones[map[i]];
+ }
+
+ ReleaseBuffer(mapBuffer);
+ }
+
+ return result;
+}
+
+/*
* visibilitymap_truncate - truncate the visibility map
*
* The caller must hold AccessExclusiveLock on the relation, to ensure that