Add pg_dump --snapshot option

Allows pg_dump to use a snapshot previously defined by a concurrent
session that has either used pg_export_snapshot() or obtained a
snapshot when creating a logical slot. When this option is used with
parallel pg_dump, the snapshot defined by this option is used and no
new snapshot is taken.

Simon Riggs and Michael Paquier

diff --git a/doc/src/sgml/ref/pg_dump.sgml b/doc/src/sgml/ref/pg_dump.sgml
index c92c6eef5d3b324b5067a62b57b829c4d57d27dd..a6e7b08e2e2f0b83e292aea1529579b92c7c32be 100644 (file)
--- a/doc/src/sgml/ref/pg_dump.sgml
+++ b/doc/src/sgml/ref/pg_dump.sgml
@@ -847,6 +847,27 @@ PostgreSQL documentation
        </listitem>
      </varlistentry>
 
+     <varlistentry>
+       <term><option>--snapshot=<replaceable class="parameter">snapshotname</replaceable></option></term>
+       <listitem>
+         <para>
+          Use the specifed synchronized snapshot when making a dump of the
+          database (see
+          <xref linkend="functions-snapshot-synchronization-table"> for more
+          details).
+         </para>
+         <para>
+          This option is useful when needing to synchronize the dump with
+          a logical replication slot (see <xref linkend="logicaldecoding">)
+          or with a concurrent session.
+         </para>
+         <para>
+          In the case of a parallel dump, the snapshot name defined by this
+          option is used rather than taking a new snapshot.
+         </para>
+       </listitem>
+     </varlistentry>
+
      <varlistentry>
       <term><option>--serializable-deferrable</option></term>
       <listitem>

diff --git a/src/bin/pg_dump/pg_dump.c b/src/bin/pg_dump/pg_dump.c
index 1e8f089224c5160a9edc756b51a2ab825ac9906e..69d359458bc878d3de546037bf5583a8c650d660 100644 (file)
--- a/src/bin/pg_dump/pg_dump.c
+++ b/src/bin/pg_dump/pg_dump.c
@@ -126,7 +126,8 @@ static const CatalogId nilCatalogId = {0, 0};
 
 static void help(const char *progname);
 static void setup_connection(Archive *AH, DumpOptions *dopt,
-                const char *dumpencoding, char *use_role);
+               const char *dumpencoding, const char *dumpsnapshot,
+               char *use_role);
 static ArchiveFormat parseArchiveFormat(const char *format, ArchiveMode *mode);
 static void expand_schema_name_patterns(Archive *fout,
                            SimpleStringList *patterns,
@@ -269,6 +270,7 @@ main(int argc, char **argv)
    RestoreOptions *ropt;
    Archive    *fout;           /* the script file */
    const char *dumpencoding = NULL;
+   const char *dumpsnapshot = NULL;
    char       *use_role = NULL;
    int         numWorkers = 1;
    trivalue    prompt_password = TRI_DEFAULT;
@@ -329,6 +331,7 @@ main(int argc, char **argv)
        {"role", required_argument, NULL, 3},
        {"section", required_argument, NULL, 5},
        {"serializable-deferrable", no_argument, &dopt->serializable_deferrable, 1},
+       {"snapshot", required_argument, NULL, 6},
        {"use-set-session-authorization", no_argument, &dopt->use_setsessauth, 1},
        {"no-security-labels", no_argument, &dopt->no_security_labels, 1},
        {"no-synchronized-snapshots", no_argument, &dopt->no_synchronized_snapshots, 1},
@@ -506,6 +509,10 @@ main(int argc, char **argv)
                set_dump_section(optarg, &dopt->dumpSections);
                break;
 
+           case 6:             /* snapshot */
+               dumpsnapshot = pg_strdup(optarg);
+               break;
+
            default:
                fprintf(stderr, _("Try \"%s --help\" for more information.\n"), progname);
                exit_nicely(1);
@@ -614,7 +621,7 @@ main(int argc, char **argv)
     * death.
     */
    ConnectDatabase(fout, dopt->dbname, dopt->pghost, dopt->pgport, dopt->username, prompt_password);
-   setup_connection(fout, dopt, dumpencoding, use_role);
+   setup_connection(fout, dopt, dumpencoding, dumpsnapshot, use_role);
 
    /*
     * Disable security label support if server version < v9.1.x (prevents
@@ -658,6 +665,11 @@ main(int argc, char **argv)
          "Run with --no-synchronized-snapshots instead if you do not need\n"
                      "synchronized snapshots.\n");
 
+   /* check the version when a snapshot is explicitly specified by user */
+   if (dumpsnapshot && fout->remoteVersion < 90200)
+       exit_horribly(NULL,
+           "Exported snapshots are not supported by this server version.\n");
+
    /* Find the last built-in OID, if needed */
    if (fout->remoteVersion < 70300)
    {
@@ -888,6 +900,7 @@ help(const char *progname)
    printf(_("  --quote-all-identifiers      quote all identifiers, even if not key words\n"));
    printf(_("  --section=SECTION            dump named section (pre-data, data, or post-data)\n"));
    printf(_("  --serializable-deferrable    wait until the dump can run without anomalies\n"));
+   printf(_("  --snapshot=SNAPSHOT          use given synchronous snapshot for the dump\n"));
    printf(_("  --use-set-session-authorization\n"
             "                               use SET SESSION AUTHORIZATION commands instead of\n"
             "                               ALTER OWNER commands to set ownership\n"));
@@ -907,7 +920,8 @@ help(const char *progname)
 }
 
 static void
-setup_connection(Archive *AH, DumpOptions *dopt, const char *dumpencoding, char *use_role)
+setup_connection(Archive *AH, DumpOptions *dopt, const char *dumpencoding,
+                const char *dumpsnapshot, char *use_role)
 {
    PGconn     *conn = GetConnection(AH);
    const char *std_strings;
@@ -1015,22 +1029,25 @@ setup_connection(Archive *AH, DumpOptions *dopt, const char *dumpencoding, char
        ExecuteSqlStatement(AH,
                            "SET TRANSACTION ISOLATION LEVEL SERIALIZABLE");
 
+   /*
+    * define an export snapshot, either chosen by user or needed for
+    * parallel dump.
+    */
+   if (dumpsnapshot)
+       AH->sync_snapshot_id = strdup(dumpsnapshot);
 
-
-   if (AH->numWorkers > 1 && AH->remoteVersion >= 90200 && !dopt->no_synchronized_snapshots)
+   if (AH->sync_snapshot_id)
    {
-       if (AH->sync_snapshot_id)
-       {
-           PQExpBuffer query = createPQExpBuffer();
-
-           appendPQExpBufferStr(query, "SET TRANSACTION SNAPSHOT ");
-           appendStringLiteralConn(query, AH->sync_snapshot_id, conn);
-           ExecuteSqlStatement(AH, query->data);
-           destroyPQExpBuffer(query);
-       }
-       else
-           AH->sync_snapshot_id = get_synchronized_snapshot(AH);
+       PQExpBuffer query = createPQExpBuffer();
+       appendPQExpBuffer(query, "SET TRANSACTION SNAPSHOT ");
+       appendStringLiteralConn(query, AH->sync_snapshot_id, conn);
+       ExecuteSqlStatement(AH, query->data);
+       destroyPQExpBuffer(query);
    }
+   else if (AH->numWorkers > 1 &&
+            AH->remoteVersion >= 90200 &&
+            !dopt->no_synchronized_snapshots)
+       AH->sync_snapshot_id = get_synchronized_snapshot(AH);
 
    if (AH->remoteVersion >= 90500)
    {
@@ -1044,7 +1061,7 @@ setup_connection(Archive *AH, DumpOptions *dopt, const char *dumpencoding, char
 static void
 setupDumpWorker(Archive *AHX, DumpOptions *dopt, RestoreOptions *ropt)
 {
-   setup_connection(AHX, dopt, NULL, NULL);
+   setup_connection(AHX, dopt, NULL, NULL, NULL);
 }
 
 static char *