Reduce test runtime of src/test/modules/snapshot_too_old.

The sto_using_cursor and sto_using_select tests were coded to exercise
every permutation of their test steps, but AFAICS there is no value in
exercising more than one.  This matters because each permutation costs
about six seconds, thanks to the "pg_sleep(6)".  Perhaps we could
reduce that, but the useless permutations seem worth getting rid of
in any case.  (Note that sto_using_hash_index got it right already.)

While here, clean up some other sloppiness such as an unused table.

This doesn't make too much difference in interactive testing, since the
wasted time is typically masked by parallelization with other tests.
However, the buildfarm runs this as a serial step, which means we can
expect to shave ~40 seconds from every buildfarm run.  That makes it
worth back-patching.

Discussion: https://postgr.es/m/2515192.1659454702@sss.pgh.pa.us

Author: tglsfdc

src/test/modules/snapshot_too_old/expected/sto_using_cursor.out

@@ -1,27 +1,5 @@
 Parsed test spec with 2 sessions
 
-starting permutation: s1decl s1f1 s1sleep s1f2 s2u
-step s1decl: DECLARE cursor1 CURSOR FOR SELECT c FROM sto1;
-step s1f1: FETCH FIRST FROM cursor1;
-c
--
-1
-(1 row)
-
-step s1sleep: SELECT setting, pg_sleep(6) FROM pg_settings WHERE name = 'old_snapshot_threshold';
-setting|pg_sleep
--------+--------
-      0|        
-(1 row)
-
-step s1f2: FETCH FIRST FROM cursor1;
-c
--
-1
-(1 row)
-
-step s2u: UPDATE sto1 SET c = 1001 WHERE c = 1;
-
 starting permutation: s1decl s1f1 s1sleep s2u s1f2
 step s1decl: DECLARE cursor1 CURSOR FOR SELECT c FROM sto1;
 step s1f1: FETCH FIRST FROM cursor1;
@@ -39,57 +17,3 @@ setting|pg_sleep
 step s2u: UPDATE sto1 SET c = 1001 WHERE c = 1;
 step s1f2: FETCH FIRST FROM cursor1;
 ERROR:  snapshot too old
-
-starting permutation: s1decl s1f1 s2u s1sleep s1f2
-step s1decl: DECLARE cursor1 CURSOR FOR SELECT c FROM sto1;
-step s1f1: FETCH FIRST FROM cursor1;
-c
--
-1
-(1 row)
-
-step s2u: UPDATE sto1 SET c = 1001 WHERE c = 1;
-step s1sleep: SELECT setting, pg_sleep(6) FROM pg_settings WHERE name = 'old_snapshot_threshold';
-setting|pg_sleep
--------+--------
-      0|        
-(1 row)
-
-step s1f2: FETCH FIRST FROM cursor1;
-ERROR:  snapshot too old
-
-starting permutation: s1decl s2u s1f1 s1sleep s1f2
-step s1decl: DECLARE cursor1 CURSOR FOR SELECT c FROM sto1;
-step s2u: UPDATE sto1 SET c = 1001 WHERE c = 1;
-step s1f1: FETCH FIRST FROM cursor1;
-c
--
-1
-(1 row)
-
-step s1sleep: SELECT setting, pg_sleep(6) FROM pg_settings WHERE name = 'old_snapshot_threshold';
-setting|pg_sleep
--------+--------
-      0|        
-(1 row)
-
-step s1f2: FETCH FIRST FROM cursor1;
-ERROR:  snapshot too old
-
-starting permutation: s2u s1decl s1f1 s1sleep s1f2
-step s2u: UPDATE sto1 SET c = 1001 WHERE c = 1;
-step s1decl: DECLARE cursor1 CURSOR FOR SELECT c FROM sto1;
-step s1f1: FETCH FIRST FROM cursor1;
-c
--
-2
-(1 row)
-
-step s1sleep: SELECT setting, pg_sleep(6) FROM pg_settings WHERE name = 'old_snapshot_threshold';
-setting|pg_sleep
--------+--------
-      0|        
-(1 row)
-
-step s1f2: FETCH FIRST FROM cursor1;
-ERROR:  snapshot too old

src/test/modules/snapshot_too_old/expected/sto_using_select.out

@@ -1,26 +1,5 @@
 Parsed test spec with 2 sessions
 
-starting permutation: s1f1 s1sleep s1f2 s2u
-step s1f1: SELECT c FROM sto1 ORDER BY c LIMIT 1;
-c
--
-1
-(1 row)
-
-step s1sleep: SELECT setting, pg_sleep(6) FROM pg_settings WHERE name = 'old_snapshot_threshold';
-setting|pg_sleep
--------+--------
-      0|        
-(1 row)
-
-step s1f2: SELECT c FROM sto1 ORDER BY c LIMIT 1;
-c
--
-1
-(1 row)
-
-step s2u: UPDATE sto1 SET c = 1001 WHERE c = 1;
-
 starting permutation: s1f1 s1sleep s2u s1f2
 step s1f1: SELECT c FROM sto1 ORDER BY c LIMIT 1;
 c
@@ -37,37 +16,3 @@ setting|pg_sleep
 step s2u: UPDATE sto1 SET c = 1001 WHERE c = 1;
 step s1f2: SELECT c FROM sto1 ORDER BY c LIMIT 1;
 ERROR:  snapshot too old
-
-starting permutation: s1f1 s2u s1sleep s1f2
-step s1f1: SELECT c FROM sto1 ORDER BY c LIMIT 1;
-c
--
-1
-(1 row)
-
-step s2u: UPDATE sto1 SET c = 1001 WHERE c = 1;
-step s1sleep: SELECT setting, pg_sleep(6) FROM pg_settings WHERE name = 'old_snapshot_threshold';
-setting|pg_sleep
--------+--------
-      0|        
-(1 row)
-
-step s1f2: SELECT c FROM sto1 ORDER BY c LIMIT 1;
-ERROR:  snapshot too old
-
-starting permutation: s2u s1f1 s1sleep s1f2
-step s2u: UPDATE sto1 SET c = 1001 WHERE c = 1;
-step s1f1: SELECT c FROM sto1 ORDER BY c LIMIT 1;
-c
--
-2
-(1 row)
-
-step s1sleep: SELECT setting, pg_sleep(6) FROM pg_settings WHERE name = 'old_snapshot_threshold';
-setting|pg_sleep
--------+--------
-      0|        
-(1 row)
-
-step s1f2: SELECT c FROM sto1 ORDER BY c LIMIT 1;
-ERROR:  snapshot too old

src/test/modules/snapshot_too_old/specs/sto_using_cursor.spec

@@ -6,14 +6,13 @@
 # granularity is in minutes.
 #
 # Since results depend on the value of old_snapshot_threshold, sneak that into
-# the line generated by the sleep, so that a surprising values isn't so hard
+# the line generated by the sleep, so that a surprising value isn't so hard
 # to identify.
 
 setup
 {
     CREATE TABLE sto1 (c int NOT NULL);
     INSERT INTO sto1 SELECT generate_series(1, 1000);
-    CREATE TABLE sto2 (c int NOT NULL);
 }
 setup
 {
@@ -22,7 +21,7 @@ setup
 
 teardown
 {
-    DROP TABLE sto1, sto2;
+    DROP TABLE sto1;
 }
 
 session "s1"
@@ -35,3 +34,5 @@ teardown		{ COMMIT; }
 
 session "s2"
 step "s2u"		{ UPDATE sto1 SET c = 1001 WHERE c = 1; }
+
+permutation "s1decl" "s1f1" "s1sleep" "s2u" "s1f2"

src/test/modules/snapshot_too_old/specs/sto_using_select.spec

@@ -6,14 +6,13 @@
 # granularity is in minutes.
 #
 # Since results depend on the value of old_snapshot_threshold, sneak that into
-# the line generated by the sleep, so that a surprising values isn't so hard
+# the line generated by the sleep, so that a surprising value isn't so hard
 # to identify.
 
 setup
 {
     CREATE TABLE sto1 (c int NOT NULL);
     INSERT INTO sto1 SELECT generate_series(1, 1000);
-    CREATE TABLE sto2 (c int NOT NULL);
 }
 setup
 {
@@ -22,7 +21,7 @@ setup
 
 teardown
 {
-    DROP TABLE sto1, sto2;
+    DROP TABLE sto1;
 }
 
 session "s1"
@@ -34,3 +33,5 @@ teardown		{ COMMIT; }
 
 session "s2"
 step "s2u"		{ UPDATE sto1 SET c = 1001 WHERE c = 1; }
+
+permutation "s1f1" "s1sleep" "s2u" "s1f2"