In pg_dump, force reconnection after issuing ALTER DATABASE SET command(s).

The folly of not doing this was exposed by the buildfarm: in some cases,
the GUC settings applied through ALTER DATABASE SET may be essential to
interpreting the reloaded data correctly.  Another argument why we can't
really get away with the scheme proposed in commit b3f840120 is that it
cannot work for parallel restore: even if the parent process manages to
hang onto the previous GUC state, worker processes would see the state
post-ALTER-DATABASE.  (Perhaps we could have dodged that bullet by
delaying DATABASE PROPERTIES restoration to the end of the run, but
that does nothing for the data semantics problem.)

This leaves us with no solution for the default_transaction_read_only issue
that commit 4bd371f6f intended to work around, other than "you gotta remove
such settings before dumping/upgrading".  However, in view of the fact that
parallel restore broke that hack years ago and no one has noticed, it's
fair to question how many people care.  I'm unexcited about adding a large
dollop of new complexity to handle that corner case.

This would be a one-liner fix, except it turns out that ReconnectToServer
tries to optimize away "redundant" reconnections.  While that may have been
valuable when coded, a quick survey of current callers shows that there are
no cases where that's actually useful, so just remove that check.  While at
it, remove the function's useless return value.

Discussion: https://postgr.es/m/12453.1516655001@sss.pgh.pa.us

diff --git a/src/bin/pg_dump/pg_backup_archiver.c b/src/bin/pg_dump/pg_backup_archiver.c
index ab009e6fe369ee7b01bf7650f0ea3354fca4a305..f55aa36c49ce5c2418c3431a5d8c56a03b329d00 100644 (file)
--- a/src/bin/pg_dump/pg_backup_archiver.c
+++ b/src/bin/pg_dump/pg_backup_archiver.c
@@ -833,8 +833,13 @@ restore_toc_entry(ArchiveHandle *AH, TocEntry *te, bool is_parallel)
                        }
                }
 
-               /* If we created a DB, connect to it... */
-               if (strcmp(te->desc, "DATABASE") == 0)
+               /*
+                * If we created a DB, connect to it.  Also, if we changed DB
+                * properties, reconnect to ensure that relevant GUC settings are
+                * applied to our session.
+                */
+               if (strcmp(te->desc, "DATABASE") == 0 ||
+                       strcmp(te->desc, "DATABASE PROPERTIES") == 0)
                {
                        PQExpBufferData connstr;
 

diff --git a/src/bin/pg_dump/pg_backup_archiver.h b/src/bin/pg_dump/pg_backup_archiver.h
index fd0d01b50690d2560b78dff69b7a15f8091a3513..becfee6e8191527c4995df57efcbc1187a3b0a5b 100644 (file)
--- a/src/bin/pg_dump/pg_backup_archiver.h
+++ b/src/bin/pg_dump/pg_backup_archiver.h
@@ -448,7 +448,7 @@ extern void InitArchiveFmt_Tar(ArchiveHandle *AH);
 
 extern bool isValidTarHeader(char *header);
 
-extern int     ReconnectToServer(ArchiveHandle *AH, const char *dbname, const char *newUser);
+extern void ReconnectToServer(ArchiveHandle *AH, const char *dbname, const char *newUser);
 extern void DropBlobIfExists(ArchiveHandle *AH, Oid oid);
 
 void           ahwrite(const void *ptr, size_t size, size_t nmemb, ArchiveHandle *AH);

diff --git a/src/bin/pg_dump/pg_backup_db.c b/src/bin/pg_dump/pg_backup_db.c
index 216853d62728d573b35c165a0e334c79dcef9583..3b7dd24151374579648bf6abe5f5467172b3d42a 100644 (file)
--- a/src/bin/pg_dump/pg_backup_db.c
+++ b/src/bin/pg_dump/pg_backup_db.c
@@ -76,13 +76,9 @@ _check_database_version(ArchiveHandle *AH)
 /*
  * Reconnect to the server.  If dbname is not NULL, use that database,
  * else the one associated with the archive handle.  If username is
- * not NULL, use that user name, else the one from the handle.  If
- * both the database and the user match the existing connection already,
- * nothing will be done.
- *
- * Returns 1 in any case.
+ * not NULL, use that user name, else the one from the handle.
  */
-int
+void
 ReconnectToServer(ArchiveHandle *AH, const char *dbname, const char *username)
 {
        PGconn     *newConn;
@@ -99,11 +95,6 @@ ReconnectToServer(ArchiveHandle *AH, const char *dbname, const char *username)
        else
                newusername = username;
 
-       /* Let's see if the request is already satisfied */
-       if (strcmp(newdbname, PQdb(AH->connection)) == 0 &&
-               strcmp(newusername, PQuser(AH->connection)) == 0)
-               return 1;
-
        newConn = _connectDB(AH, newdbname, newusername);
 
        /* Update ArchiveHandle's connCancel before closing old connection */
@@ -111,8 +102,6 @@ ReconnectToServer(ArchiveHandle *AH, const char *dbname, const char *username)
 
        PQfinish(AH->connection);
        AH->connection = newConn;
-
-       return 1;
 }
 
 /*

diff --git a/src/bin/pg_dump/pg_dump.c b/src/bin/pg_dump/pg_dump.c
index 11e1ba04cc4ea722f082d905680e5b8dad887e45..d65ea54a69bfb392da864335fe2c4a13dc951afb 100644 (file)
--- a/src/bin/pg_dump/pg_dump.c
+++ b/src/bin/pg_dump/pg_dump.c
@@ -2819,10 +2819,11 @@ dumpDatabase(Archive *fout)
 
        /*
         * Now construct a DATABASE PROPERTIES archive entry to restore any
-        * non-default database-level properties.  We want to do this after
-        * reconnecting so that these properties won't apply during the restore
-        * session.  In this way, restoring works even if there is, say, an ALTER
-        * DATABASE SET that turns on default_transaction_read_only.
+        * non-default database-level properties.  (The reason this must be
+        * separate is that we cannot put any additional commands into the TOC
+        * entry that has CREATE DATABASE.  pg_restore would execute such a group
+        * in an implicit transaction block, and the backend won't allow CREATE
+        * DATABASE in that context.)
         */
        resetPQExpBuffer(creaQry);
        resetPQExpBuffer(delQry);
@@ -2854,8 +2855,7 @@ dumpDatabase(Archive *fout)
 
        /*
         * We stick this binary-upgrade query into the DATABASE PROPERTIES archive
-        * entry, too.  It can't go into the DATABASE entry because that would
-        * result in an implicit transaction block around the CREATE DATABASE.
+        * entry, too, for lack of a better place.
         */
        if (dopt->binary_upgrade)
        {