pgsql: Reduce scope of heap vacuum per_buffer_data

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(at)sss(dot)pgh(dot)pa(dot)us>
Discussion: https://postgr.es/m/626104.1739729538%40sss.pgh.pa.us

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/c623e8593ec4ee6987f3cd9350ced7caf8526ed2

Modified Files
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src/backend/access/heap/vacuumlazy.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)