From c1afd175b5b2e5c44f6da34988342e00ecdfb518 Mon Sep 17 00:00:00 2001 From: Peter Geoghegan Date: Wed, 20 Mar 2019 10:41:36 -0700 Subject: Allow amcheck to re-find tuples using new search. Teach contrib/amcheck's bt_index_parent_check() function to take advantage of the uniqueness property of heapkeyspace indexes in support of a new verification option: non-pivot tuples (non-highkey tuples on the leaf level) can optionally be re-found using a new search for each, that starts from the root page. If a tuple cannot be re-found, report that the index is corrupt. The new "rootdescend" verification option is exhaustive, and can therefore make a call to bt_index_parent_check() take a lot longer. Re-finding tuples during verification is mostly intended as an option for backend developers, since the corruption scenarios that it alone is uniquely capable of detecting seem fairly far-fetched. For example, "rootdescend" verification is much more likely to detect corruption of the least significant byte of a key from a pivot tuple in the root page of a B-Tree that already has at least three levels. Typically, only a few tuples on a cousin leaf page are at risk of "getting overlooked" by index scans in this scenario. The corrupt key in the root page is only slightly corrupt: corrupt enough to give wrong answers to some queries, and yet not corrupt enough to allow the problem to be detected without verifying agreement between the leaf page and the root page, skipping at least one internal page level. The existing bt_index_parent_check() checks never cross more than a single level. Author: Peter Geoghegan Reviewed-By: Heikki Linnakangas Discussion: https://postgr.es/m/CAH2-Wz=yTWnVu+HeHGKb2AGiADL9eprn-cKYAto4MkKOuiGtRQ@mail.gmail.com --- doc/src/sgml/amcheck.sgml | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-) (limited to 'doc/src') diff --git a/doc/src/sgml/amcheck.sgml b/doc/src/sgml/amcheck.sgml index 8bb60d5c2da..627651d8d4a 100644 --- a/doc/src/sgml/amcheck.sgml +++ b/doc/src/sgml/amcheck.sgml @@ -112,7 +112,7 @@ ORDER BY c.relpages DESC LIMIT 10; - bt_index_parent_check(index regclass, heapallindexed boolean) returns void + bt_index_parent_check(index regclass, heapallindexed boolean, rootdescend boolean) returns void bt_index_parent_check @@ -126,7 +126,10 @@ ORDER BY c.relpages DESC LIMIT 10; argument is true, the function verifies the presence of all heap tuples that should be found within the index, and that there are no missing downlinks in the index - structure. The checks that can be performed by + structure. When the optional rootdescend + argument is true, verification re-finds + tuples on the leaf level by performing a new search from the + root page for each tuple. The checks that can be performed by bt_index_parent_check are a superset of the checks that can be performed by bt_index_check. bt_index_parent_check can be thought of as -- cgit v1.2.3