Use fake LSNs to improve nbtree dropPin behavior. Use fake LSNs in all nbtree critical sections that write a WAL record. That way we can safely apply the _bt_killitems LSN trick with logged and unlogged indexes alike. This brings the same benefits to plain scans of unlogged relations that commit 2ed5b87f brought to plain scans of logged relations: scans will drop their leaf page pin eagerly (by applying the "dropPin" optimization), which avoids blocking progress by VACUUM. This is particularly helpful with applications that allow a scrollable cursor to remain idle for long periods.
Preparation for an upcoming commit that will add the amgetbatch interface, and switch nbtree over to it (from amgettuple) to enable I/O prefetching. The index prefetching read stream's effective prefetch distance is adversely affected by any buffer pins held by the index AM. At the same time, it can be useful for prefetching to read dozens of leaf pages ahead of the scan to maintain an adequate prefetch distance. The index prefetching patch avoids this tension by always eagerly dropping index page pins of the kind traditionally held as an interlock against unsafe concurrent TID recycling by VACUUM (essentially the same way that amgetbitmap routines have always avoided holding onto pins). The work from this commit makes that possible during scans of nbtree unlogged indexes -- without our having to give up on setting LP_DEAD bits on index tuples altogether. Follow-up to commit d774072f, which moved the fake LSN infrastructure out of GiST so that it could be used by other index AMs. Author: Peter Geoghegan <[email protected]> Reviewed-By: Andres Freund <[email protected]> Reviewed-By: Tomas Vondra <[email protected]> Discussion: https://postgr.es/m/cah2-wzkehuhxyua8quc7rrn3etnxpiksjpfo8mhb+0dr2k0...@mail.gmail.com Branch ------ master Details ------- https://git.postgresql.org/pg/commitdiff/8a879119a1d12ff0a410fe3b64ad15069c3a377c Modified Files -------------- src/backend/access/nbtree/README | 5 +-- src/backend/access/nbtree/nbtdedup.c | 8 ++-- src/backend/access/nbtree/nbtinsert.c | 46 +++++++++++--------- src/backend/access/nbtree/nbtpage.c | 82 ++++++++++++++++++++--------------- src/backend/access/nbtree/nbtree.c | 8 ---- src/backend/access/nbtree/nbtsearch.c | 1 - src/backend/access/nbtree/nbtutils.c | 1 - 7 files changed, 79 insertions(+), 72 deletions(-)
