nbtree: Avoid allocating _bt_search stack. Avoid allocating memory for an nbtree descent stack during index scans. We only require a descent stack during inserts, when it is used to determine where to insert a new pivot tuple/downlink into the target leaf page's parent page in the event of a page split. (Page deletion's first phase also performs a _bt_search that requires a descent stack.)
This optimization improves performance by minimizing palloc churn. It speeds up index scans that call _bt_search frequently/descend the index many times, especially when the cost of scanning the index dominates (e.g., with index-only skip scans). Testing has shown that the underlying issue causes performance problems for an upcoming patch that will replace btgettuple with a new btgetbatch interface to enable I/O prefetching. Author: Peter Geoghegan <[email protected]> Reviewed-By: Tomas Vondra <[email protected]> Discussion: https://postgr.es/m/cah2-wzmy7nmba9k8m_vz-xndzjeuqbu8teleel960-rakb-...@mail.gmail.com Branch ------ master Details ------- https://git.postgresql.org/pg/commitdiff/d071e1cfec23505e0f55f06988c0144f16235586 Modified Files -------------- contrib/amcheck/verify_nbtree.c | 4 +--- src/backend/access/nbtree/nbtinsert.c | 19 ++++++++++++++++++- src/backend/access/nbtree/nbtpage.c | 2 +- src/backend/access/nbtree/nbtsearch.c | 35 ++++++++++++++++++----------------- src/backend/access/nbtree/nbtutils.c | 16 ---------------- src/include/access/nbtree.h | 3 +-- 6 files changed, 39 insertions(+), 40 deletions(-)
