Support disabling index bypassing by VACUUM.

Generalize the INDEX_CLEANUP VACUUM parameter (and the corresponding
reloption): make it into a ternary style boolean parameter.  It now
exposes a third option, "auto".  The "auto" option (which is now the
default) enables the "bypass index vacuuming" optimization added by
commit 1e55e7d1.

"VACUUM (INDEX_CLEANUP TRUE)" is redefined to once again make VACUUM
simply do any required index vacuuming, regardless of how few dead
tuples are encountered during the first scan of the target heap relation
(unless there are exactly zero).  This gives users a way of opting out
of the "bypass index vacuuming" optimization, if for whatever reason
that proves necessary.  It is also expected to be used by PostgreSQL
developers as a testing option from time to time.

"VACUUM (INDEX_CLEANUP FALSE)" does the same thing as it always has: it
forcibly disables both index vacuuming and index cleanup.  It's not
expected to be used much in PostgreSQL 14.  The failsafe mechanism added
by commit 1e55e7d1 addresses the same problem in a simpler way.
INDEX_CLEANUP can now be thought of as a testing and compatibility
option.

Author: Peter Geoghegan <pg@bowt.ie>
Reviewed-By: Masahiko Sawada <sawada.mshk@gmail.com>
Reviewed-By: Justin Pryzby <pryzby@telsasoft.com>
Discussion: https://postgr.es/m/CAH2-WznrBoCST4_Gxh_G9hA8NzGUbeBGnOUC8FcXcrhqsv6OHQ@mail.gmail.com

2 files changed, 22 insertions, 13 deletions

diff --git a/src/include/commands/vacuum.h b/src/include/commands/vacuum.h
index cb27257bb65..bf3126aa9bb 100644
--- a/src/include/commands/vacuum.h
+++ b/src/include/commands/vacuum.h
@@ -185,17 +185,20 @@ typedef struct VacAttrStats
 #define VACOPT_DISABLE_PAGE_SKIPPING 0x80	/* don't skip any pages */
 
 /*
- * A ternary value used by vacuum parameters.
+ * Values used by index_cleanup and truncate params.
  *
- * DEFAULT value is used to determine the value based on other
- * configurations, e.g. reloptions.
+ * VACOPTVALUE_UNSPECIFIED is used as an initial placeholder when VACUUM
+ * command has no explicit value.  When that happens the final usable value
+ * comes from the corresponding reloption (though the reloption default is
+ * usually used).
  */
-typedef enum VacOptTernaryValue
+typedef enum VacOptValue
 {
-	VACOPT_TERNARY_DEFAULT = 0,
-	VACOPT_TERNARY_DISABLED,
-	VACOPT_TERNARY_ENABLED,
-} VacOptTernaryValue;
+	VACOPTVALUE_UNSPECIFIED = 0,
+	VACOPTVALUE_AUTO,
+	VACOPTVALUE_DISABLED,
+	VACOPTVALUE_ENABLED,
+} VacOptValue;
 
 /*
  * Parameters customizing behavior of VACUUM and ANALYZE.
@@ -216,10 +219,8 @@ typedef struct VacuumParams
 	int			log_min_duration;	/* minimum execution threshold in ms at
 									 * which  verbose logs are activated, -1
 									 * to use default */
-	VacOptTernaryValue index_cleanup;	/* Do index vacuum and cleanup,
-										 * default value depends on reloptions */
-	VacOptTernaryValue truncate;	/* Truncate empty pages at the end,
-									 * default value depends on reloptions */
+	VacOptValue index_cleanup;	/* Do index vacuum and cleanup */
+	VacOptValue truncate;		/* Truncate empty pages at the end */
 
 	/*
 	 * The number of parallel vacuum workers.  0 by default which means choose
diff --git a/src/include/utils/rel.h b/src/include/utils/rel.h
index 774ac5b2b19..77d176a9348 100644
--- a/src/include/utils/rel.h
+++ b/src/include/utils/rel.h
@@ -307,6 +307,14 @@ typedef struct AutoVacOpts
 	float8		analyze_scale_factor;
 } AutoVacOpts;
 
+/* StdRdOptions->vacuum_index_cleanup values */
+typedef enum StdRdOptIndexCleanup
+{
+	STDRD_OPTION_VACUUM_INDEX_CLEANUP_AUTO = 0,
+	STDRD_OPTION_VACUUM_INDEX_CLEANUP_OFF,
+	STDRD_OPTION_VACUUM_INDEX_CLEANUP_ON
+} StdRdOptIndexCleanup;
+
 typedef struct StdRdOptions
 {
 	int32		vl_len_;		/* varlena header (do not touch directly!) */
@@ -316,7 +324,7 @@ typedef struct StdRdOptions
 	AutoVacOpts autovacuum;		/* autovacuum-related options */
 	bool		user_catalog_table; /* use as an additional catalog relation */
 	int			parallel_workers;	/* max number of parallel workers */
-	bool		vacuum_index_cleanup;	/* enables index vacuuming and cleanup */
+	StdRdOptIndexCleanup vacuum_index_cleanup;	/* controls index vacuuming */
 	bool		vacuum_truncate;	/* enables vacuum to truncate a relation */
 } StdRdOptions;