pgsql: Restore vacuum_delay_point() in GIN posting-tree leaf vacuum

Restore vacuum_delay_point() in GIN posting-tree leaf vacuum

Commit fd83c83d094 turned the recursive posting-tree cleanup in
ginVacuumPostingTreeLeaves() into an iterative sweep that follows the
tree's leaf pages via their rightlinks. The recursive version called
vacuum_delay_point() while processing the tree, but that call was removed
and never re-added to the new loop. As that commit only set out to fix a
deadlock, the removal appears to have been unintentional.

Consequently the leaf-page sweep of a single posting tree runs with no
vacuum_delay_point(), and therefore no CHECK_FOR_INTERRUPTS(). A posting
tree stores all the TIDs for one indexed key, so for a frequently
occurring key it can span a large number of leaf pages. While such a
tree is being vacuumed the operation ignores vacuum_cost_delay and does
not respond to query cancellation or statement_timeout; an autovacuum
worker likewise cannot be interrupted mid-sweep when another backend
requests a conflicting lock.

Restore the call, placed after the current page has been unlocked and
released so that no buffer content lock is held across a potential delay
(cf. 21c27af65fb). The sibling loops in ginbulkdelete() and
ginvacuumcleanup() already call vacuum_delay_point() once per page.

Author: Paul Kim <mok03127(at)gmail(dot)com>
Co-authored-by: Alexander Korotkov <aekorotkov(at)gmail(dot)com>
Reviewed-by: Michael Paquier <michael(at)paquier(dot)xyz>
Reviewed-by: Andrey Borodin <x4mmm(at)yandex-team(dot)ru>
Reviewed-by: solai v <solai(dot)cdac(at)gmail(dot)com>
Discussion: https://postgr.es/m/178447127453.110.12276981925360691905%40mail.gmail.com
Backpatch-through: 14

Branch
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REL_16_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/006ac761e5080de9934fde8aac027d8c0ac82048

Modified Files
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src/backend/access/gin/ginvacuum.c | 7 +++++++
1 file changed, 7 insertions(+)