[BACKPORT 2024.1][#21930] YSQL: Fix Bitmap Scans corrupted results fo…

…r rechecked text columns

Summary:
Original commit: 237dad5 / D35399

=== Problem ===
Queries with recheck conditions on text columns had corrupted values:
```lang=sql
create table test_recheck_text(a text);
insert into test_recheck_text VALUES ('i');
create index on test_recheck_text(a ASC);

/*+ BitmapScan(t) Set(yb_enable_bitmapscan true) */
SELECT * FROM test_recheck_text AS t WHERE a = 'i' AND a < 'j';
                                    a
----------------------------------------------------------------------------
 \x7F\x7F\x7F\x7F\x7F\x7F\x7F\x7F\x7F\x7F\x7F\x7F\x7F\x7F\x7F\x7F\x7F\x7F
(1 row)
```

This is because of allocating parts of the tuple into a memory context that gets reset when evaluating recheck conditions.

=== Explanation ===

While implementing Bitmap Scans, I had copied two patterns that do not work well together:

First, from `nodeBitmapHeapscan.c`:
```lang=c
/*
 * If we are using lossy info, we have to recheck the qual
 * conditions at every tuple.
 */
if (tbmres->recheck)
{
	econtext->ecxt_scantuple = slot;
	if (!ExecQualAndReset(node->bitmapqualorig, econtext))
	{
		/* Fails recheck, so drop it and loop back for another */
		InstrCountFiltered2(node, 1);
		ExecClearTuple(slot);
		continue;
	}
}
```

second, from `ybSeqScan.c`:
```lang=c
/* capture all fetch allocations in the short-lived context */
oldcontext = MemoryContextSwitchTo(econtext->ecxt_per_tuple_memory);
ybFetchNext(ybScan->handle, slot,
            RelationGetRelid(node->ss.ss_currentRelation));
MemoryContextSwitchTo(oldcontext);
```

`nodeYbBitmapTablescan.c` had the following flow:
```
lang=c

oldcontext = MemoryContextSwitchTo(econtext->ecxt_per_tuple_memory);
ybFetchNext() // load tuple into ecxt_per_tuple_memory
MemoryContextSwitchTo(oldcontext);

...

if (node->recheck_required)
{
	if (!ExecQualAndReset(node->recheck_local_quals, econtext)) // reset ecxt_per_tuple_memory!!
	        ...
}
```
`ybFetchNext` loaded any allocations associated with the tuple into `ecxt_per_tuple_memory`. Then `ExecQualAndReset` cleared it.

These two operations clearly don't work well together, and explain the corrupted value of the query - the allocations associated with the tuple were freed before we could use them.

The solution is to fetch the tuple into a longer-lived memory context OR change `ExecQualAndReset` to `ExecQual`. The first option is more desirable, because we can let the tuples themselves live longer while the intermediate results of `ExecQual` can be freed as soon as possible.
Jira: DB-10845

Test Plan:
```
./yb_build.sh  --java-test 'org.yb.pgsql.TestPgRegressYbBitmapScans'
```

Reviewers: tnayak, amartsinchyk, mtakahara

Reviewed By: tnayak

Subscribers: yql

Tags: #jenkins-ready

Differential Revision: https://phorge.dev.yugabyte.com/D35631

src/postgres/src/backend/executor/nodeYbBitmapTablescan.c

@@ -46,7 +46,6 @@ YbBitmapTableNext(YbBitmapTableScanState *node)
 	YbTBMIterateResult *ybtbmres;
 	HeapScanDesc scandesc;
 	ExprContext *econtext;
-	MemoryContext oldcontext;
 	YbScanDesc ybScan;
 
 	/*
@@ -131,11 +130,8 @@ YbBitmapTableNext(YbBitmapTableScanState *node)
 		/* We have yb_fetch_row_limit rows fetched, get them one by one */
 		while (true)
 		{
-			/* capture all fetch allocations in the short-lived context */
-			oldcontext = MemoryContextSwitchTo(econtext->ecxt_per_tuple_memory);
 			ybFetchNext(ybScan->handle, slot,
 						RelationGetRelid(node->ss.ss_currentRelation));
-			MemoryContextSwitchTo(oldcontext);
 
 			if (ybtbmres)
 				++ybtbmres->index;

src/postgres/src/test/regress/expected/yb_bitmap_scans.out

@@ -1056,6 +1056,33 @@ INSERT INTO test_false VALUES (1, 1), (2, 2);
                Storage Index Read Requests: 1
 (12 rows)
 
+--
+-- #21930: test recheck conditions on text columns
+--
+CREATE TABLE test_recheck_text(a TEXT);
+INSERT INTO test_recheck_text(a) VALUES ('i');
+CREATE INDEX ON test_recheck_text(a ASC);
+/*+ BitmapScan(t) */ EXPLAIN (ANALYZE, DIST, COSTS OFF, SUMMARY OFF)
+SELECT * FROM test_recheck_text AS t WHERE a = 'i' AND a < 'j';
+                                 QUERY PLAN
+----------------------------------------------------------------------------
+ YB Bitmap Table Scan on test_recheck_text t (actual rows=1 loops=1)
+   Storage Recheck Cond: ((a < 'j'::text) AND (a = 'i'::text))
+   Storage Table Read Requests: 1
+   Storage Table Rows Scanned: 1
+   ->  Bitmap Index Scan on test_recheck_text_a_idx (actual rows=1 loops=1)
+         Index Cond: ((a < 'j'::text) AND (a = 'i'::text))
+         Storage Index Read Requests: 1
+         Storage Index Rows Scanned: 1
+(8 rows)
+
+/*+ BitmapScan(t) */
+SELECT * FROM test_recheck_text AS t WHERE a = 'i' AND a < 'j';
+ a
+---
+ i
+(1 row)
+
 --
 -- test recheck index conditions
 --

src/postgres/src/test/regress/expected/yb_bitmap_scans_colo.out

@@ -1086,6 +1086,34 @@ INSERT INTO test_false VALUES (1, 1), (2, 2);
                Storage Index Read Requests: 1
 (13 rows)
 
+--
+-- #21930: test recheck conditions on text columns
+--
+CREATE TABLE test_recheck_text(a TEXT);
+INSERT INTO test_recheck_text(a) VALUES ('i');
+CREATE INDEX ON test_recheck_text(a ASC);
+/*+ BitmapScan(t) */ EXPLAIN (ANALYZE, DIST, COSTS OFF, SUMMARY OFF)
+SELECT * FROM test_recheck_text AS t WHERE a = 'i' AND a < 'j';
+                                 QUERY PLAN
+----------------------------------------------------------------------------
+ YB Bitmap Table Scan on test_recheck_text t (actual rows=1 loops=1)
+   Storage Recheck Cond: ((a < 'j'::text) AND (a = 'i'::text))
+   Storage Table Read Requests: 1
+   Storage Table Rows Scanned: 1
+   ->  Bitmap Index Scan on test_recheck_text_a_idx (actual rows=1 loops=1)
+         Index Cond: ((a < 'j'::text) AND (a = 'i'::text))
+         Storage Table Rows Scanned: 1
+         Storage Index Read Requests: 1
+         Storage Index Rows Scanned: 1
+(9 rows)
+
+/*+ BitmapScan(t) */
+SELECT * FROM test_recheck_text AS t WHERE a = 'i' AND a < 'j';
+ a
+---
+ i
+(1 row)
+
 --
 -- test recheck index conditions
 --

src/postgres/src/test/regress/sql/yb_bitmap_scans.sql

@@ -264,6 +264,18 @@ INSERT INTO test_false VALUES (1, 1), (2, 2);
 /*+ BitmapScan(test_false) */ EXPLAIN (ANALYZE, DIST, COSTS OFF, SUMMARY OFF) SELECT * FROM test_false WHERE (a <= 1 AND a = 2);
 /*+ BitmapScan(test_false) */ EXPLAIN (ANALYZE, DIST, COSTS OFF, SUMMARY OFF) SELECT * FROM test_false WHERE (a = 1 AND a = 2) OR b = 0;
 
+--
+-- #21930: test recheck conditions on text columns
+--
+CREATE TABLE test_recheck_text(a TEXT);
+INSERT INTO test_recheck_text(a) VALUES ('i');
+CREATE INDEX ON test_recheck_text(a ASC);
+
+/*+ BitmapScan(t) */ EXPLAIN (ANALYZE, DIST, COSTS OFF, SUMMARY OFF)
+SELECT * FROM test_recheck_text AS t WHERE a = 'i' AND a < 'j';
+/*+ BitmapScan(t) */
+SELECT * FROM test_recheck_text AS t WHERE a = 'i' AND a < 'j';
+
 --
 -- test recheck index conditions
 --

src/postgres/src/test/regress/sql/yb_bitmap_scans_colo.sql

@@ -272,6 +272,18 @@ INSERT INTO test_false VALUES (1, 1), (2, 2);
 /*+ BitmapScan(test_false) */ EXPLAIN (ANALYZE, DIST, COSTS OFF, SUMMARY OFF) SELECT * FROM test_false WHERE (a <= 1 AND a = 2);
 /*+ BitmapScan(test_false) */ EXPLAIN (ANALYZE, DIST, COSTS OFF, SUMMARY OFF) SELECT * FROM test_false WHERE (a = 1 AND a = 2) OR b = 0;
 
+--
+-- #21930: test recheck conditions on text columns
+--
+CREATE TABLE test_recheck_text(a TEXT);
+INSERT INTO test_recheck_text(a) VALUES ('i');
+CREATE INDEX ON test_recheck_text(a ASC);
+
+/*+ BitmapScan(t) */ EXPLAIN (ANALYZE, DIST, COSTS OFF, SUMMARY OFF)
+SELECT * FROM test_recheck_text AS t WHERE a = 'i' AND a < 'j';
+/*+ BitmapScan(t) */
+SELECT * FROM test_recheck_text AS t WHERE a = 'i' AND a < 'j';
+
 --
 -- test recheck index conditions
 --