pg_dump: Lock all relations, not just plain tables

Now that LOCK TABLE can take any relation type, acquire lock on all
relations that are to be dumped.  This prevents schema changes or
deadlock errors that could cause a dump to fail after expending much
effort.  The server is tested to have the capability and the feature
disabled if it doesn't, so that a patched pg_dump doesn't fail when
connecting to an unpatched server.

Backpatch to 9.5.

Author: Álvaro Herrera <[email protected]>
Reviewed-by: Tom Lane <[email protected]>
Reported-by: Wells Oliver <[email protected]>
Discussion: https://postgr.es/m/20201021200659[email protected]

diff --git a/src/bin/pg_dump/pg_backup.h b/src/bin/pg_dump/pg_backup.h
index a6a8e6f2fd864b3887c640e88df00ced00033610..6c79319164144107ccc7cfe5e393798b4ca825d3 100644 (file)
--- 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 5ba43441f50aa111182ee488bb995efe18f5d617..28b2892538aec63141832c92e2616679687b534d 100644 (file)
--- 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_class_tblspc_relfilenode_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_class_tblspc_relfilenode_index",
+                                 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 8888dd34b9b00994bcd03ab308ec914d9c00139d..355beec1f7c7f6a33dfe030164c898477f3d30ea 100644 (file)
--- 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 ff45e3fb8c3797179f71ba377dddea57af9e289b..03f9d4d9e84f723b91af1ba1e3b9ffe23756f244 100644 (file)
--- 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);