Fix "ANALYZE t, t" inside a transaction block.

tglsfdc · tglsfdc · commit cabe0f298ea7 · 2019-08-10T11:30:11.000-04:00
This failed with either "tuple already updated by self" or "duplicate key value violates unique constraint", depending on whether the table had previously been analyzed or not. The reason is that ANALYZE tried to insert or update the same pg_statistic rows twice, and there was no CommandCounterIncrement between. So add one. The same case works fine outside a transaction block, because then there's a whole transaction boundary between, as a consequence of the way VACUUM works. This issue has been latent all along, but the problem was unreachable before commit 11d8d72 added the ability to specify multiple tables in ANALYZE. We could, perhaps, alternatively fix it by adding code to de-duplicate the list of VacuumRelations --- but that would add a lot of overhead to work around dumb commands, so it's not attractive. Per bug #15946 from Yaroslav Schekin. Back-patch to v11. (Note: in v11 I also back-patched the test added by commit 2322456; otherwise the problem doesn't manifest in the test I added, because "vactst" is empty when the tests for multiple ANALYZE targets are reached. That seems like not a very good thing anyway, so I did this rather than rethinking the choice of test case.) Discussion: https://postgr.es/m/15946-5c7570a2884a26cf@postgresql.org
diff --git a/src/backend/commands/vacuum.c b/src/backend/commands/vacuum.c
@@ -418,6 +418,15 @@ vacuum(List *relations, VacuumParams *params,
 					PopActiveSnapshot();
 					CommitTransactionCommand();
 				}
+				else
+				{
+					/*
+					 * If we're not using separate xacts, better separate the
+					 * ANALYZE actions with CCIs.  This avoids trouble if user
+					 * says "ANALYZE t, t".
+					 */
+					CommandCounterIncrement();
+				}
 			}
 		}
 	}
diff --git a/src/test/regress/expected/vacuum.out b/src/test/regress/expected/vacuum.out
@@ -180,6 +180,10 @@ ANALYZE vactst, does_not_exist, vacparted;
 ERROR:  relation "does_not_exist" does not exist
 ANALYZE vactst (i), vacparted (does_not_exist);
 ERROR:  column "does_not_exist" of relation "vacparted" does not exist
+ANALYZE vactst, vactst;
+BEGIN;  -- ANALYZE behaves differently inside a transaction block
+ANALYZE vactst, vactst;
+COMMIT;
 -- parenthesized syntax for ANALYZE
 ANALYZE (VERBOSE) does_not_exist;
 ERROR:  relation "does_not_exist" does not exist
diff --git a/src/test/regress/sql/vacuum.sql b/src/test/regress/sql/vacuum.sql
@@ -147,6 +147,10 @@ ANALYZE vactst, vacparted;
 ANALYZE vacparted (b), vactst;
 ANALYZE vactst, does_not_exist, vacparted;
 ANALYZE vactst (i), vacparted (does_not_exist);
+ANALYZE vactst, vactst;
+BEGIN;  -- ANALYZE behaves differently inside a transaction block
+ANALYZE vactst, vactst;
+COMMIT;
 
 -- parenthesized syntax for ANALYZE
 ANALYZE (VERBOSE) does_not_exist;

Original file line number	Diff line number	Diff line change
`@@ -418,6 +418,15 @@ vacuum(List relations, VacuumParams params,`
`418`	`418`	`PopActiveSnapshot();`
`419`	`419`	`CommitTransactionCommand();`
`420`	`420`	`}`
	`421`	`+ else`
	`422`	`+ {`
	`423`	`+ /*`
	`424`	`+ * If we're not using separate xacts, better separate the`
	`425`	`+ * ANALYZE actions with CCIs. This avoids trouble if user`
	`426`	`+ * says "ANALYZE t, t".`
	`427`	`+ */`
	`428`	`+ CommandCounterIncrement();`
	`429`	`+ }`
`421`	`430`	`}`
`422`	`431`	`}`
`423`	`432`	`}`