Rename VACOPT_NOWAIT to VACOPT_SKIP_LOCKED

When it comes to SELECT ... FOR or LOCK, NOWAIT means to not wait for
something to happen, and issue an error.  SKIP LOCKED means to not wait
for something to happen but to move on without issuing an error.  The
internal option of autovacuum and autoanalyze mentioned above, used only
when wraparound is not involved was named NOWAIT, but behaves like SKIP
LOCKED which is confusing.

Author: Nathan Bossart
Discussion: https://postgr.es/m/20180307050345.GA3095@paquier.xyz

src/backend/commands/analyze.c

@@ -143,7 +143,7 @@ analyze_rel(Oid relid, RangeVar *relation, int options,
 	 * matter if we ever try to accumulate stats on dead tuples.) If the rel
 	 * has been dropped since we last saw it, we don't need to process it.
 	 */
-	if (!(options & VACOPT_NOWAIT))
+	if (!(options & VACOPT_SKIP_LOCKED))
 		onerel = try_relation_open(relid, ShareUpdateExclusiveLock);
 	else if (ConditionalLockRelationOid(relid, ShareUpdateExclusiveLock))
 		onerel = try_relation_open(relid, NoLock);

src/backend/commands/vacuum.c

@@ -1377,7 +1377,7 @@ vacuum_rel(Oid relid, RangeVar *relation, int options, VacuumParams *params)
 	 * If we've been asked not to wait for the relation lock, acquire it first
 	 * in non-blocking mode, before calling try_relation_open().
 	 */
-	if (!(options & VACOPT_NOWAIT))
+	if (!(options & VACOPT_SKIP_LOCKED))
 		onerel = try_relation_open(relid, lmode);
 	else if (ConditionalLockRelationOid(relid, lmode))
 		onerel = try_relation_open(relid, NoLock);

src/backend/postmaster/autovacuum.c

@@ -2904,7 +2904,7 @@ table_recheck_autovac(Oid relid, HTAB *table_toast_map,
 		tab->at_vacoptions = VACOPT_SKIPTOAST |
 			(dovacuum ? VACOPT_VACUUM : 0) |
 			(doanalyze ? VACOPT_ANALYZE : 0) |
-			(!wraparound ? VACOPT_NOWAIT : 0);
+			(!wraparound ? VACOPT_SKIP_LOCKED : 0);
 		tab->at_params.freeze_min_age = freeze_min_age;
 		tab->at_params.freeze_table_age = freeze_table_age;
 		tab->at_params.multixact_freeze_min_age = multixact_freeze_min_age;

src/include/nodes/parsenodes.h

@@ -3135,7 +3135,8 @@ typedef enum VacuumOption
 	VACOPT_VERBOSE = 1 << 2,	/* print progress info */
 	VACOPT_FREEZE = 1 << 3,		/* FREEZE option */
 	VACOPT_FULL = 1 << 4,		/* FULL (non-concurrent) vacuum */
-	VACOPT_NOWAIT = 1 << 5,		/* don't wait to get lock (autovacuum only) */
+	VACOPT_SKIP_LOCKED = 1 << 5,	/* skip if cannot get lock (autovacuum
+									 * only) */
 	VACOPT_SKIPTOAST = 1 << 6,	/* don't process the TOAST table, if any */
 	VACOPT_DISABLE_PAGE_SKIPPING = 1 << 7	/* don't skip any pages */
 } VacuumOption;