Make local buffers pin limit more conservative GetLocalPinLimit() and GetAdditionalLocalPinLimit(), currently in use only by the read stream, previously allowed a backend to pin all num_temp_buffers local buffers. This meant that the read stream could use every available local buffer for read-ahead, leaving none for other concurrent pin-holders like other read streams and related buffers like the visibility map buffer needed during on-access pruning.
This became more noticeable since b46e1e54d07, which allows on-access pruning to set the visibility map, which meant that some scans also needed to pin a page of the VM. It caused a test in src/test/regress/sql/temp.sql to fail in some cases. Cap the local pin limit to num_temp_buffers / 4, providing some headroom. This doesn't guarantee that all needed pins will be available — for example, a backend can still open more cursors than there are buffers — but it makes it less likely that read-ahead will exhaust the pool. Note that these functions are not limited by definition to use in the read stream; however, this cap should be appropriate in other contexts. Reported-by: Alexander Lakhin <[email protected]> Author: Melanie Plageman <[email protected]> Reviewed-by: Andres Freund <[email protected]> Discussion: https://postgr.es/m/97529f5a-ec10-46b1-ab50-4653126c6889%40gmail.com Branch ------ master Details ------- https://git.postgresql.org/pg/commitdiff/da6874635db2e8ab95150481c992f03ec6094805 Modified Files -------------- src/backend/storage/buffer/localbuf.c | 14 +++++++++++--- 1 file changed, 11 insertions(+), 3 deletions(-)
