On 2020-Oct-21, Tom Lane wrote:
> Alvaro Herrera <alvherre@xxxxxxxxxxxxxx> writes:
> > Here's a quick patchset that makes pg_dump do LOCK TABLE on all
> > relations it dumps; patch 0001 allows server-side LOCK TABLE to run on
> > any relkind, and then 0002 makes pg_dump test for that capability at
> > connection start, and if it exists, then it's used for all relations to
> > dump.
>
> I think the "test for that capability" bit needs more subtlety.
Great ideas, thanks -- all adopted in the attached version. I didn't
test this with 9.5 but as you say NOWAIT is already supported there and
the command itself does work.
Since the wrong-object error was thrown before the lock-unavailable
error, and both before the ACL check, it works to test for those codes
specifically; it's not a problem if the lock is unavailable or denied.
Right now if any other error occurs in the LOCK TABLE, pg_dump aborts
with an error. I don't know what that could be. I suppose if it dies
with OOM then it doesn't matter whether it's here or elsewhere.
Testing for a view as I was doing was not good, because PG12 does allow
locks on views. I decided to use pg_aggregate_fnoid_index because it's
easier for manual tests: it doesn't prevent connecting to the database
when a strong lock is held. This in contrast with other more obvious
candidates. It's a pretty arbitrary choice but it shouldn't harm
anything since we don't actually hold the lock for more than an instant,
and that only if it's not contended.
I discovered once again that fallthrough comment handling in combination
with ccache are pretty obnoxious.
>From e09e08a25771dc1d84d8ed690d16ce6fdcb121a5 Mon Sep 17 00:00:00 2001
From: Alvaro Herrera <alvherre@xxxxxxxxxxxxxx>
Date: Tue, 7 Jul 2020 18:45:39 -0400
Subject: [PATCH v2 1/2] accept any relkind in LOCK TABLE
---
src/backend/commands/lockcmds.c | 8 --------
1 file changed, 8 deletions(-)
diff --git a/src/backend/commands/lockcmds.c b/src/backend/commands/lockcmds.c
index d8cafc42bb..d9ff71aa69 100644
--- a/src/backend/commands/lockcmds.c
+++ b/src/backend/commands/lockcmds.c
@@ -83,14 +83,6 @@ RangeVarCallbackForLockTable(const RangeVar *rv, Oid relid, Oid oldrelid,
return; /* woops, concurrently dropped; no permissions
* check */
- /* Currently, we only allow plain tables or views to be locked */
- if (relkind != RELKIND_RELATION && relkind != RELKIND_PARTITIONED_TABLE &&
- relkind != RELKIND_VIEW)
- ereport(ERROR,
- (errcode(ERRCODE_WRONG_OBJECT_TYPE),
- errmsg("\"%s\" is not a table or view",
- rv->relname)));
-
/*
* Make note if a temporary relation has been accessed in this
* transaction.
--
2.20.1
>From edd11eacc2ae4fdb868e831f5fabdf3668640417 Mon Sep 17 00:00:00 2001
From: Alvaro Herrera <alvherre@xxxxxxxxxxxxxx>
Date: Tue, 7 Jul 2020 19:14:21 -0400
Subject: [PATCH v2 2/2] pg_dump: lock all rels, not just RELKIND_RELATION
---
src/bin/pg_dump/pg_backup.h | 2 ++
src/bin/pg_dump/pg_backup_db.c | 64 ++++++++++++++++++++++++++++++++++
src/bin/pg_dump/pg_backup_db.h | 2 ++
src/bin/pg_dump/pg_dump.c | 17 +++++----
4 files changed, 78 insertions(+), 7 deletions(-)
diff --git a/src/bin/pg_dump/pg_backup.h b/src/bin/pg_dump/pg_backup.h
index a6a8e6f2fd..6c79319164 100644
--- a/src/bin/pg_dump/pg_backup.h
+++ b/src/bin/pg_dump/pg_backup.h
@@ -198,6 +198,8 @@ typedef struct Archive
int minRemoteVersion; /* allowable range */
int maxRemoteVersion;
+ bool hasGenericLockTable; /* can LOCK TABLE do non-table rels */
+
int numWorkers; /* number of parallel processes */
char *sync_snapshot_id; /* sync snapshot id for parallel operation */
diff --git a/src/bin/pg_dump/pg_backup_db.c b/src/bin/pg_dump/pg_backup_db.c
index 5ba43441f5..a9eba97b84 100644
--- a/src/bin/pg_dump/pg_backup_db.c
+++ b/src/bin/pg_dump/pg_backup_db.c
@@ -531,6 +531,70 @@ EndDBCopyMode(Archive *AHX, const char *tocEntryTag)
}
}
+/*
+ * Does LOCK TABLE work on non-table relations on this server?
+ *
+ * Note: assumes it is called out of any transaction
+ */
+bool
+IsLockTableGeneric(Archive *AHX)
+{
+ ArchiveHandle *AH = (ArchiveHandle *) AHX;
+ PGresult *res;
+ char *sqlstate;
+ bool retval;
+
+ if (AHX->remoteVersion >= 140000)
+ return true;
+ else if (AHX->remoteVersion < 90500)
+ return false;
+
+ StartTransaction(AHX);
+
+ /*
+ * Try a LOCK TABLE on a well-known non-table catalog; WRONG_OBJECT_TYPE
+ * tells us that this server doesn't support locking non-table rels, while
+ * LOCK_NOT_AVAILABLE and INSUFFICIENT_PRIVILEGE tell us that it does.
+ * Report anything else as a fatal problem.
+ */
+#define ERRCODE_INSUFFICIENT_PRIVILEGE "42501"
+#define ERRCODE_WRONG_OBJECT_TYPE "42809"
+#define ERRCODE_LOCK_NOT_AVAILABLE "55P03"
+ res = PQexec(AH->connection,
+ "LOCK TABLE pg_catalog.pg_aggregate_fnoid_index IN ACCESS SHARE MODE NOWAIT");
+ switch (PQresultStatus(res))
+ {
+ case PGRES_COMMAND_OK:
+ retval = true;
+ break;
+ case PGRES_FATAL_ERROR:
+ sqlstate = PQresultErrorField(res, PG_DIAG_SQLSTATE);
+ if (strcmp(sqlstate, ERRCODE_WRONG_OBJECT_TYPE) == 0)
+ {
+ retval = false;
+ break;
+ }
+ else if (strcmp(sqlstate, ERRCODE_LOCK_NOT_AVAILABLE) == 0 ||
+ strcmp(sqlstate, ERRCODE_INSUFFICIENT_PRIVILEGE) == 0)
+ {
+ retval = true;
+ break;
+ }
+ /* else, falls through */
+ default:
+ warn_or_exit_horribly(AH, "LOCK TABLE failed for \"%s\": %s",
+ "pg_catalog.pg_stats",
+ PQerrorMessage(AH->connection));
+ retval = false; /* not reached */
+ break;
+ }
+ PQclear(res);
+
+ CommitTransaction(AHX);
+
+ return retval;
+}
+
void
StartTransaction(Archive *AHX)
{
diff --git a/src/bin/pg_dump/pg_backup_db.h b/src/bin/pg_dump/pg_backup_db.h
index 8888dd34b9..355beec1f7 100644
--- a/src/bin/pg_dump/pg_backup_db.h
+++ b/src/bin/pg_dump/pg_backup_db.h
@@ -20,6 +20,8 @@ extern PGresult *ExecuteSqlQueryForSingleRow(Archive *fout, const char *query);
extern void EndDBCopyMode(Archive *AHX, const char *tocEntryTag);
+extern bool IsLockTableGeneric(Archive *AHX);
+
extern void StartTransaction(Archive *AHX);
extern void CommitTransaction(Archive *AHX);
diff --git a/src/bin/pg_dump/pg_dump.c b/src/bin/pg_dump/pg_dump.c
index ff45e3fb8c..03f9d4d9e8 100644
--- a/src/bin/pg_dump/pg_dump.c
+++ b/src/bin/pg_dump/pg_dump.c
@@ -1176,6 +1176,9 @@ setup_connection(Archive *AH, const char *dumpencoding,
ExecuteSqlStatement(AH, "SET row_security = off");
}
+ /* Detect whether LOCK TABLE can handle non-table relations */
+ AH->hasGenericLockTable = IsLockTableGeneric(AH);
+
/*
* Start transaction-snapshot mode transaction to dump consistent data.
*/
@@ -6843,16 +6846,16 @@ getTables(Archive *fout, int *numTables)
* assume our lock on the child is enough to prevent schema
* alterations to parent tables.
*
- * NOTE: it'd be kinda nice to lock other relations too, not only
- * plain or partitioned tables, but the backend doesn't presently
- * allow that.
- *
- * We only need to lock the table for certain components; see
+ * We only need to lock the relation for certain components; see
* pg_dump.h
+ *
+ * On server versions that support it, we lock all relations not just
+ * plain tables.
*/
if (tblinfo[i].dobj.dump &&
- (tblinfo[i].relkind == RELKIND_RELATION ||
- tblinfo->relkind == RELKIND_PARTITIONED_TABLE) &&
+ (fout->hasGenericLockTable ||
+ tblinfo[i].relkind == RELKIND_PARTITIONED_TABLE ||
+ tblinfo[i].relkind == RELKIND_RELATION) &&
(tblinfo[i].dobj.dump & DUMP_COMPONENTS_REQUIRING_LOCK))
{
resetPQExpBuffer(query);
--
2.20.1
