logictest: fix probable flake around using old stats cache entry

We just saw a failure in a logic test that verifies the number of
parallel lookup joins based on the recently added heuristic. I couldn't
immediately reproduce it, but I think what happened was that we used
a stale stats cache entry which didn't pick up the newly-collected table
stats. In this test we need precise control of which stats are used, so
this commit clears the stats cache before each query where we need it.

Release note: None

Author: yuzefovich

pkg/ccl/logictestccl/testdata/logic_test/regional_by_row_cascade

@@ -58,6 +58,10 @@ INSERT INTO child (c, p, crdb_region) VALUES (1000, 100, 'us-east-1'), (2000, 20
 statement ok
 ANALYZE great_grandparent;
 
+# Clear the stat cache so that the new statistic is guaranteed to be used.
+statement ok
+SELECT crdb_internal.clear_table_stats_cache();
+
 # Only the scan in the main query is parallelized when we don't have stats on
 # the descendant tables.
 query I
@@ -68,6 +72,10 @@ SELECT count(*) FROM [EXPLAIN (VERBOSE) DELETE FROM great_grandparent WHERE i =
 statement ok
 ANALYZE grandparent;
 
+# Clear the stat cache so that the new statistic is guaranteed to be used.
+statement ok
+SELECT crdb_internal.clear_table_stats_cache();
+
 # Now we also should parallelize lookup join into the grandparent table.
 query I
 SELECT count(*) FROM [EXPLAIN (VERBOSE) DELETE FROM great_grandparent WHERE i = 1] WHERE info LIKE '%parallel%';
@@ -77,6 +85,10 @@ SELECT count(*) FROM [EXPLAIN (VERBOSE) DELETE FROM great_grandparent WHERE i =
 statement ok
 ANALYZE parent;
 
+# Clear the stat cache so that the new statistic is guaranteed to be used.
+statement ok
+SELECT crdb_internal.clear_table_stats_cache();
+
 # Now we also should parallelize lookup join into the parent table.
 query I
 SELECT count(*) FROM [EXPLAIN (VERBOSE) DELETE FROM great_grandparent WHERE i = 1] WHERE info LIKE '%parallel%';
@@ -86,6 +98,10 @@ SELECT count(*) FROM [EXPLAIN (VERBOSE) DELETE FROM great_grandparent WHERE i =
 statement ok
 ANALYZE child;
 
+# Clear the stat cache so that the new statistic is guaranteed to be used.
+statement ok
+SELECT crdb_internal.clear_table_stats_cache();
+
 # Finally, all three lookup joins as well as the scan in the main query should
 # be parallelized.
 query T
@@ -288,6 +304,10 @@ ALTER TABLE grandparent INJECT STATISTICS '[
     }
 ]'
 
+# Clear the stat cache so that the new statistic is guaranteed to be used.
+statement ok
+SELECT crdb_internal.clear_table_stats_cache();
+
 query I
 SELECT count(*) FROM [EXPLAIN (VERBOSE) DELETE FROM great_grandparent WHERE i = 1] WHERE info LIKE '%parallel%';
 ----
@@ -329,6 +349,10 @@ ALTER TABLE grandparent INJECT STATISTICS '[
     }
 ]'
 
+# Clear the stat cache so that the new statistic is guaranteed to be used.
+statement ok
+SELECT crdb_internal.clear_table_stats_cache();
+
 query I
 SELECT count(*) FROM [EXPLAIN (VERBOSE) DELETE FROM great_grandparent WHERE i = 1] WHERE info LIKE '%parallel%';
 ----