pgsql: Recycle deleted nbtree pages more aggressively.

Recycle deleted nbtree pages more aggressively.

Commit 61b313e4 made nbtree consistently pass down a heaprel to low
level routines like _bt_getbuf(). Although this was primarily intended
as preparation for logical decoding on standbys, it also made it easy to
correct an old deficiency in how nbtree VACUUM determines whether or not
it's now safe to recycle deleted pages.

Pass the heaprel to GlobalVisTestFor() in nbtree routines that deal with
recycle safety. nbtree now makes less pessimistic assumptions about
recycle safety within non-catalog relations. This enhancement
complements the recycling enhancement added by commit 9dd963ae25.

nbtree remains just as pessimistic as ever when it comes to recycle
safety within indexes on catalog relations. There is no fundamental
reason why we need to treat catalog relations differently, though. The
behavioral inconsistency is a consequence of the way that nbtree uses
nextXID values to implement what Lanin and Shasha call "the drain
technique". Note in particular that it has nothing to do with whether
or not index tuples might still be required for an older MVCC snapshot.

Author: Bertrand Drouvot <bertranddrouvot(dot)pg(at)gmail(dot)com>
Discussion: https://postgr.es/m/CAH2-WzkaiDxCje0yPuH=3Uh2p1V_2pFGY==xfbZoZu7Ax_NB8g@mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/e48c817395e1cdc85dbecc4ff3c18e34983ae3f2

Modified Files
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src/backend/access/nbtree/nbtpage.c | 7 ++++---
src/backend/access/nbtree/nbtree.c | 3 ++-
src/include/access/nbtree.h | 8 ++------
3 files changed, 8 insertions(+), 10 deletions(-)