Reduce scope of heap vacuum per_buffer_data

Move lazy_scan_heap()'s per_buffer_data variable into a tighter scope.
In lazy_scan_heap()'s phase I heap vacuuming, the read stream API
returns a pointer to the next block number to vacuum. As long as
read_stream_next_buffer() returns a valid buffer, per_buffer_data should
always be valid.

Move per_buffer_data into a tighter scope and make sure it is reset to
NULL on each iteration so that we get a core dump instead of bogus data
from a previous block if something goes wrong in the read stream API.

Suggested-by: Tom Lane <tgl@sss.pgh.pa.us>
Discussion: https://postgr.es/m/626104.1739729538%40sss.pgh.pa.us

diff --git a/src/backend/access/heap/vacuumlazy.c b/src/backend/access/heap/vacuumlazy.c
index 911f68b413dacc8cc8fef3bf07d5f1e63ed1c093..1af18a78a2b1dd862d16145a7666ad29417a8477 100644 (file)
--- a/src/backend/access/heap/vacuumlazy.c
+++ b/src/backend/access/heap/vacuumlazy.c
@@ -1192,7 +1192,6 @@ lazy_scan_heap(LVRelState *vacrel)
        BlockNumber rel_pages = vacrel->rel_pages,
                                blkno = 0,
                                next_fsm_block_to_vacuum = 0;
-       void       *per_buffer_data = NULL;
        BlockNumber orig_eager_scan_success_limit =
                vacrel->eager_scan_remaining_successes; /* for logging */
        Buffer          vmbuffer = InvalidBuffer;
@@ -1231,6 +1230,7 @@ lazy_scan_heap(LVRelState *vacrel)
                Page            page;
                uint8           blk_info = 0;
                bool            has_lpdead_items;
+               void       *per_buffer_data = NULL;
                bool            vm_page_frozen = false;
                bool            got_cleanup_lock = false;