Disable vacuum page skipping in selected test cases.

By default VACUUM will skip pages that it can't immediately get
exclusive access to, which means that even activities as harmless
and unpredictable as checkpoint buffer writes might prevent a page
from being processed.  Ordinarily this is no big deal, but we have
a small number of test cases that examine the results of VACUUM's
processing and therefore will fail if the page of interest is skipped.
This seems to be the explanation for some rare buildfarm failures.
To fix, add the DISABLE_PAGE_SKIPPING option to the VACUUM commands
in tests where this could be an issue.

In passing, remove a duplicated query in pageinspect/sql/page.sql.

Back-patch as necessary (some of these cases are as old as v10).

Discussion: https://postgr.es/m/413923.1611006484@sss.pgh.pa.us

2 files changed, 6 insertions, 22 deletions

diff --git a/contrib/pageinspect/expected/page.out b/contrib/pageinspect/expected/page.out
index 4cd0db80183..4da28f0a1db 100644
--- a/contrib/pageinspect/expected/page.out
+++ b/contrib/pageinspect/expected/page.out
@@ -1,7 +1,7 @@
 CREATE EXTENSION pageinspect;
 CREATE TABLE test1 (a int, b int);
 INSERT INTO test1 VALUES (16777217, 131584);
-VACUUM test1;  -- set up FSM
+VACUUM (DISABLE_PAGE_SKIPPING) test1;  -- set up FSM
 -- The page contents can vary, so just test that it can be read
 -- successfully, but don't keep the output.
 SELECT octet_length(get_raw_page('test1', 'main', 0)) AS main_0;
@@ -87,18 +87,8 @@ SELECT * FROM fsm_page_contents(get_raw_page('test1', 'fsm', 0));
 (1 row)
 
 -- If we freeze the only tuple on test1, the infomask should
--- always be the same in all test runs. we show raw flags by
--- default: HEAP_XMIN_COMMITTED and HEAP_XMIN_INVALID.
-VACUUM FREEZE test1;
-SELECT t_infomask, t_infomask2, raw_flags, combined_flags
-FROM heap_page_items(get_raw_page('test1', 0)),
-     LATERAL heap_tuple_infomask_flags(t_infomask, t_infomask2);
- t_infomask | t_infomask2 |                         raw_flags                         |   combined_flags   
-------------+-------------+-----------------------------------------------------------+--------------------
-       2816 |           2 | {HEAP_XMIN_COMMITTED,HEAP_XMIN_INVALID,HEAP_XMAX_INVALID} | {HEAP_XMIN_FROZEN}
-(1 row)
-
--- output the decoded flag HEAP_XMIN_FROZEN instead
+-- always be the same in all test runs.
+VACUUM (FREEZE, DISABLE_PAGE_SKIPPING) test1;
 SELECT t_infomask, t_infomask2, raw_flags, combined_flags
 FROM heap_page_items(get_raw_page('test1', 0)),
      LATERAL heap_tuple_infomask_flags(t_infomask, t_infomask2);
diff --git a/contrib/pageinspect/sql/page.sql b/contrib/pageinspect/sql/page.sql
index 01844cb629c..d333b763d70 100644
--- a/contrib/pageinspect/sql/page.sql
+++ b/contrib/pageinspect/sql/page.sql
@@ -3,7 +3,7 @@ CREATE EXTENSION pageinspect;
 CREATE TABLE test1 (a int, b int);
 INSERT INTO test1 VALUES (16777217, 131584);
 
-VACUUM test1;  -- set up FSM
+VACUUM (DISABLE_PAGE_SKIPPING) test1;  -- set up FSM
 
 -- The page contents can vary, so just test that it can be read
 -- successfully, but don't keep the output.
@@ -34,19 +34,13 @@ SELECT tuple_data_split('test1'::regclass, t_data, t_infomask, t_infomask2, t_bi
 SELECT * FROM fsm_page_contents(get_raw_page('test1', 'fsm', 0));
 
 -- If we freeze the only tuple on test1, the infomask should
--- always be the same in all test runs. we show raw flags by
--- default: HEAP_XMIN_COMMITTED and HEAP_XMIN_INVALID.
-VACUUM FREEZE test1;
+-- always be the same in all test runs.
+VACUUM (FREEZE, DISABLE_PAGE_SKIPPING) test1;
 
 SELECT t_infomask, t_infomask2, raw_flags, combined_flags
 FROM heap_page_items(get_raw_page('test1', 0)),
      LATERAL heap_tuple_infomask_flags(t_infomask, t_infomask2);
 
--- output the decoded flag HEAP_XMIN_FROZEN instead
-SELECT t_infomask, t_infomask2, raw_flags, combined_flags
-FROM heap_page_items(get_raw_page('test1', 0)),
-     LATERAL heap_tuple_infomask_flags(t_infomask, t_infomask2);
-
 -- tests for decoding of combined flags
 -- HEAP_XMAX_SHR_LOCK = (HEAP_XMAX_EXCL_LOCK | HEAP_XMAX_KEYSHR_LOCK)
 SELECT * FROM heap_tuple_infomask_flags(x'0050'::int, 0);