postgres.git / summary / log / commit / refs

commit    9e85b20da7cd89eb0fc503d4dd48f5fc86b45f64
Author:   Peter Geoghegan <pg@bowt.ie>
Date:     Thu Dec 19 16:08:53 2024 +0000
First released in: 18.0, 17.3

    Avoid nbtree index scan SAOP scanBehind confusion.
    
    Consistently reset so->scanBehind at the beginning of nbtree array
    advancement, even during sktrig_required=false calls (calls where array
    advancement is triggered by an unsatisfied non-required array scan key).
    Otherwise, it's possible for queries to fail to return all relevant
    tuples to the scan given a low-order required scan key that was
    previously deemed "satisfied" by a truncated high key attribute value.
    This only happened at the point where a later non-required array scan
    key needed to be "advanced" once on the next leaf page (that is, once
    the right sibling of the truncated high key page was reached).
    
    The underlying issue was that later code within _bt_advance_array_keys
    assumed that the so->scanBehind flag must have been set using the
    current page's high key (not the previous page's high key).  Any later
    successful recheck call to _bt_check_compare would therefore spuriously
    be prevented from making _bt_advance_array_keys return true, based on
    the faulty belief that the truncated attribute must be from the scan's
    current tuple (i.e. the non-pivot tuple at the start of the next page).
    _bt_advance_array_keys would return false for the tuple, ultimately
    resulting in _bt_checkkeys failing to return a matching tuple.
    
    Oversight in commit 5bf748b8, which enhanced nbtree ScalarArrayOp
    execution.
    
    Author: Peter Geoghegan <pg@bowt.ie>
    Discussion: https://postgr.es/m/CAH2-WzkJKncfqyAUTeuB5GgRhT1vhsWO2q11dbZNqKmvjopP_g@mail.gmail.com
    Backpatch: 17-, where commit 5bf748b8 first appears.


 src/backend/access/nbtree/nbtutils.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/src/backend/access/nbtree/nbtutils.c b/src/backend/access/nbtree/nbtutils.c
index 8d047d8873f..878f4b2e7b8 100644
--- a/src/backend/access/nbtree/nbtutils.c
+++ b/src/backend/access/nbtree/nbtutils.c
@@ -1800,6 +1800,12 @@ _bt_advance_array_keys(IndexScanDesc scan, BTReadPageState *pstate,
 				all_required_satisfied = true,
 				all_satisfied = true;
 
+	/*
+	 * Unset so->scanBehind in case it is still set from back when we dealt
+	 * with the previous page's high key/finaltup
+	 */
+	so->scanBehind = false;
+
 	if (sktrig_required)
 	{
 		/*
@@ -1808,8 +1814,6 @@ _bt_advance_array_keys(IndexScanDesc scan, BTReadPageState *pstate,
 		Assert(!_bt_tuple_before_array_skeys(scan, dir, tuple, tupdesc,
 											 tupnatts, false, 0, NULL));
 
-		so->scanBehind = false; /* reset */
-
 		/*
 		 * Required scan key wasn't satisfied, so required arrays will have to
 		 * advance.  Invalidate page-level state that tracks whether the


[parent: 7b8d45d278de]