pg_surgery: Try to stabilize regression tests.

According to buildfarm member sungazer, the behavior of VACUUM can be
unstable in these tests even if we prevent autovacuum from running on
the tables in question, apparently because even a manual vacuum can
behave differently depending on whether anything else is running that
holds back the global xmin. So use a temporary table instead, which
as of commit a7212be8b9 enables
vacuuming using a more aggressive cutoff.

This approach can't be used for the regression test that involves a
materialized view, but that test doesn't run vacuum, so it shouldn't
be prone to this particular failure mode.

Analysis by Tom Lane. Patch by Ashutosh Sharma and me.

Discussion: http://postgr.es/m/665524.1599948007@sss.pgh.pa.us

contrib/pg_surgery/expected/heap_surgery.out

@@ -1,8 +1,7 @@
 create extension pg_surgery;
 -- create a normal heap table and insert some rows.
--- note that we don't commit the transaction, so autovacuum can't interfere.
-begin;
-create table htab(a int);
+-- use a temp table so that vacuum behavior doesn't depend on global xmin
+create temp table htab (a int);
 insert into htab values (100), (200), (300), (400), (500);
 -- test empty TID array
 select heap_force_freeze('htab'::regclass, ARRAY[]::tid[]);
@@ -85,9 +84,9 @@ NOTICE:  skipping tid (0, 6) for relation "htab" because the item number is out
  
 (1 row)
 
-rollback;
 -- set up a new table with a redirected line pointer
-create table htab2(a int) with (autovacuum_enabled = off);
+-- use a temp table so that vacuum behavior doesn't depend on global xmin
+create temp table htab2(a int);
 insert into htab2 values (100);
 update htab2 set a = 200;
 vacuum htab2;
@@ -175,6 +174,5 @@ ERROR:  "vw" is not a table, materialized view, or TOAST table
 select heap_force_freeze('vw'::regclass, ARRAY['(0, 1)']::tid[]);
 ERROR:  "vw" is not a table, materialized view, or TOAST table
 -- cleanup.
-drop table htab2;
 drop view vw;
 drop extension pg_surgery;

contrib/pg_surgery/sql/heap_surgery.sql

@@ -1,9 +1,8 @@
 create extension pg_surgery;
 
 -- create a normal heap table and insert some rows.
--- note that we don't commit the transaction, so autovacuum can't interfere.
-begin;
-create table htab(a int);
+-- use a temp table so that vacuum behavior doesn't depend on global xmin
+create temp table htab (a int);
 insert into htab values (100), (200), (300), (400), (500);
 
 -- test empty TID array
@@ -38,10 +37,9 @@ select ctid, xmax from htab where xmin = 2;
 -- out-of-range TIDs should be skipped
 select heap_force_freeze('htab'::regclass, ARRAY['(0, 0)', '(0, 6)']::tid[]);
 
-rollback;
-
 -- set up a new table with a redirected line pointer
-create table htab2(a int) with (autovacuum_enabled = off);
+-- use a temp table so that vacuum behavior doesn't depend on global xmin
+create temp table htab2(a int);
 insert into htab2 values (100);
 update htab2 set a = 200;
 vacuum htab2;
@@ -86,6 +84,5 @@ select heap_force_kill('vw'::regclass, ARRAY['(0, 1)']::tid[]);
 select heap_force_freeze('vw'::regclass, ARRAY['(0, 1)']::tid[]);
 
 -- cleanup.
-drop table htab2;
 drop view vw;
 drop extension pg_surgery;