pg_dump: allow multiple rows per insert

This is useful to speed up loading data in a different database engine.

Authors: Surafel Temesgen and David Rowley.  Lightly edited by Álvaro.
Reviewed-by: Fabien Coelho
Discussion: https://postgr.es/m/CALAY4q9kumSdnRBzvRJvSRf2+BH20YmSvzqOkvwpEmodD-xv6g@mail.gmail.com

Author: alvherre

doc/src/sgml/ref/pg_dump.sgml

@@ -661,9 +661,9 @@ PostgreSQL documentation
         ...</literal>).  This will make restoration very slow; it is mainly
         useful for making dumps that can be loaded into
         non-<productname>PostgreSQL</productname> databases.
-        However, since this option generates a separate command for each row,
-        an error in reloading a row causes only that row to be lost rather
-        than the entire table contents.
+        Any error during reloading will cause only rows that are part of the
+        problematic <command>INSERT</command> to be lost, rather than the
+        entire table contents.
        </para>
       </listitem>
      </varlistentry>
@@ -775,13 +775,12 @@ PostgreSQL documentation
         than <command>COPY</command>).  This will make restoration very slow;
         it is mainly useful for making dumps that can be loaded into
         non-<productname>PostgreSQL</productname> databases.
-        However, since this option generates a separate command for each row,
-        an error in reloading a row causes only that row to be lost rather
-        than the entire table contents.
-        Note that
-        the restore might fail altogether if you have rearranged column order.
-        The <option>--column-inserts</option> option is safe against column
-        order changes, though even slower.
+        Any error during reloading will cause only rows that are part of the
+        problematic <command>INSERT</command> to be lost, rather than the
+        entire table contents.  Note that the restore might fail altogether if
+        you have rearranged column order.  The
+        <option>--column-inserts</option> option is safe against column order
+        changes, though even slower.
        </para>
       </listitem>
      </varlistentry>
@@ -925,8 +924,9 @@ PostgreSQL documentation
        <para>
         Add <literal>ON CONFLICT DO NOTHING</literal> to
         <command>INSERT</command> commands.
-        This option is not valid unless <option>--inserts</option> or
-        <option>--column-inserts</option> is also specified.
+        This option is not valid unless <option>--inserts</option>,
+        <option>--column-inserts</option> or
+        <option>--rows-per-insert</option> is also specified.
        </para>
       </listitem>
      </varlistentry>
@@ -949,6 +949,20 @@ PostgreSQL documentation
       </listitem>
      </varlistentry>
 
+     <varlistentry>
+      <term><option>--rows-per-insert=<replaceable class="parameter">nrows</replaceable></option></term>
+      <listitem>
+       <para>
+        Dump data as <command>INSERT</command> commands (rather than
+        <command>COPY</command>).  Controls the maximum number of rows per
+        <command>INSERT</command> command. The value specified must be a
+        number greater than zero.  Any error during reloading will cause only
+        rows that are part of the problematic <command>INSERT</command> to be
+        lost, rather than the entire table contents.
+       </para>
+      </listitem>
+     </varlistentry>
+
      <varlistentry>
        <term><option>--section=<replaceable class="parameter">sectionname</replaceable></option></term>
        <listitem>

src/bin/pg_dump/pg_backup.h

@@ -140,10 +140,10 @@ typedef struct _dumpOptions
 	int			dumpSections;	/* bitmask of chosen sections */
 	bool		aclsSkip;
 	const char *lockWaitTimeout;
+	int			dump_inserts;	/* 0 = COPY, otherwise rows per INSERT */
 
 	/* flags for various command-line long options */
 	int			disable_dollar_quoting;
-	int			dump_inserts;
 	int			column_inserts;
 	int			if_exists;
 	int			no_comments;

src/bin/pg_dump/pg_dump.c

@@ -138,6 +138,12 @@ static const CatalogId nilCatalogId = {0, 0};
 static bool have_extra_float_digits = false;
 static int extra_float_digits;
 
+/*
+ * The default number of rows per INSERT when
+ * --inserts is specified without --rows-per-insert
+ */
+#define DUMP_DEFAULT_ROWS_PER_INSERT 1
+
 /*
  * Macro for producing quoted, schema-qualified name of a dumpable object.
  */
@@ -306,11 +312,13 @@ main(int argc, char **argv)
 	DumpableObject *boundaryObjs;
 	int			i;
 	int			optindex;
+	char	   *endptr;
 	RestoreOptions *ropt;
 	Archive    *fout;			/* the script file */
 	const char *dumpencoding = NULL;
 	const char *dumpsnapshot = NULL;
 	char	   *use_role = NULL;
+	long		rowsPerInsert;
 	int			numWorkers = 1;
 	trivalue	prompt_password = TRI_DEFAULT;
 	int			compressLevel = -1;
@@ -363,7 +371,7 @@ main(int argc, char **argv)
 		{"exclude-table-data", required_argument, NULL, 4},
 		{"extra-float-digits", required_argument, NULL, 8},
 		{"if-exists", no_argument, &dopt.if_exists, 1},
-		{"inserts", no_argument, &dopt.dump_inserts, 1},
+		{"inserts", no_argument, NULL, 9},
 		{"lock-wait-timeout", required_argument, NULL, 2},
 		{"no-tablespaces", no_argument, &dopt.outputNoTablespaces, 1},
 		{"quote-all-identifiers", no_argument, &quote_all_identifiers, 1},
@@ -382,6 +390,7 @@ main(int argc, char **argv)
 		{"no-subscriptions", no_argument, &dopt.no_subscriptions, 1},
 		{"no-sync", no_argument, NULL, 7},
 		{"on-conflict-do-nothing", no_argument, &dopt.do_nothing, 1},
+		{"rows-per-insert", required_argument, NULL, 10},
 
 		{NULL, 0, NULL, 0}
 	};
@@ -572,6 +581,31 @@ main(int argc, char **argv)
 				}
 				break;
 
+			case 9:				/* inserts */
+
+				/*
+				 * dump_inserts also stores --rows-per-insert, careful not to
+				 * overwrite that.
+				 */
+				if (dopt.dump_inserts == 0)
+					dopt.dump_inserts = DUMP_DEFAULT_ROWS_PER_INSERT;
+				break;
+
+			case 10:			/* rows per insert */
+				errno = 0;
+				rowsPerInsert = strtol(optarg, &endptr, 10);
+
+				if (endptr == optarg || *endptr != '\0' ||
+					rowsPerInsert <= 0 || rowsPerInsert > INT_MAX ||
+					errno == ERANGE)
+				{
+					write_msg(NULL, "rows-per-insert must be in range %d..%d\n",
+							  1, INT_MAX);
+					exit_nicely(1);
+				}
+				dopt.dump_inserts = (int) rowsPerInsert;
+				break;
+
 			default:
 				fprintf(stderr, _("Try \"%s --help\" for more information.\n"), progname);
 				exit_nicely(1);
@@ -596,8 +630,8 @@ main(int argc, char **argv)
 	}
 
 	/* --column-inserts implies --inserts */
-	if (dopt.column_inserts)
-		dopt.dump_inserts = 1;
+	if (dopt.column_inserts && dopt.dump_inserts == 0)
+		dopt.dump_inserts = DUMP_DEFAULT_ROWS_PER_INSERT;
 
 	/*
 	 * Binary upgrade mode implies dumping sequence data even in schema-only
@@ -622,8 +656,12 @@ main(int argc, char **argv)
 	if (dopt.if_exists && !dopt.outputClean)
 		exit_horribly(NULL, "option --if-exists requires option -c/--clean\n");
 
-	if (dopt.do_nothing && !(dopt.dump_inserts || dopt.column_inserts))
-		exit_horribly(NULL, "option --on-conflict-do-nothing requires option --inserts or --column-inserts\n");
+	/*
+	 * --inserts are already implied above if --column-inserts or
+	 * --rows-per-insert were specified.
+	 */
+	if (dopt.do_nothing && dopt.dump_inserts == 0)
+		exit_horribly(NULL, "option --on-conflict-do-nothing requires option --inserts, --rows-per-insert or --column-inserts\n");
 
 	/* Identify archive format to emit */
 	archiveFormat = parseArchiveFormat(format, &archiveMode);
@@ -993,6 +1031,7 @@ help(const char *progname)
 	printf(_("  --no-unlogged-table-data     do not dump unlogged table data\n"));
 	printf(_("  --on-conflict-do-nothing     add ON CONFLICT DO NOTHING to INSERT commands\n"));
 	printf(_("  --quote-all-identifiers      quote all identifiers, even if not key words\n"));
+	printf(_("  --rows-per-insert=NROWS      number of rows per INSERT; implies --inserts\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 snapshot for the dump\n"));
@@ -1909,9 +1948,9 @@ dumpTableData_insert(Archive *fout, void *dcontext)
 	PQExpBuffer q = createPQExpBuffer();
 	PQExpBuffer insertStmt = NULL;
 	PGresult   *res;
-	int			tuple;
 	int			nfields;
-	int			field;
+	int			rows_per_statement = dopt->dump_inserts;
+	int			rows_this_statement = 0;
 
 	appendPQExpBuffer(q, "DECLARE _pg_dump_cursor CURSOR FOR "
 					  "SELECT * FROM ONLY %s",
@@ -1926,69 +1965,88 @@ dumpTableData_insert(Archive *fout, void *dcontext)
 		res = ExecuteSqlQuery(fout, "FETCH 100 FROM _pg_dump_cursor",
 							  PGRES_TUPLES_OK);
 		nfields = PQnfields(res);
-		for (tuple = 0; tuple < PQntuples(res); tuple++)
+
+		/*
+		 * First time through, we build as much of the INSERT statement as
+		 * possible in "insertStmt", which we can then just print for each
+		 * statement. If the table happens to have zero columns then this will
+		 * be a complete statement, otherwise it will end in "VALUES" and be
+		 * ready to have the row's column values printed.
+		 */
+		if (insertStmt == NULL)
 		{
-			/*
-			 * First time through, we build as much of the INSERT statement as
-			 * possible in "insertStmt", which we can then just print for each
-			 * line. If the table happens to have zero columns then this will
-			 * be a complete statement, otherwise it will end in "VALUES(" and
-			 * be ready to have the row's column values appended.
-			 */
-			if (insertStmt == NULL)
-			{
-				TableInfo  *targettab;
+			TableInfo  *targettab;
 
-				insertStmt = createPQExpBuffer();
+			insertStmt = createPQExpBuffer();
 
-				/*
-				 * When load-via-partition-root is set, get the root table
-				 * name for the partition table, so that we can reload data
-				 * through the root table.
-				 */
-				if (dopt->load_via_partition_root && tbinfo->ispartition)
-					targettab = getRootTableInfo(tbinfo);
-				else
-					targettab = tbinfo;
+			/*
+			 * When load-via-partition-root is set, get the root table name
+			 * for the partition table, so that we can reload data through the
+			 * root table.
+			 */
+			if (dopt->load_via_partition_root && tbinfo->ispartition)
+				targettab = getRootTableInfo(tbinfo);
+			else
+				targettab = tbinfo;
 
-				appendPQExpBuffer(insertStmt, "INSERT INTO %s ",
-								  fmtQualifiedDumpable(targettab));
+			appendPQExpBuffer(insertStmt, "INSERT INTO %s ",
+							  fmtQualifiedDumpable(targettab));
 
-				/* corner case for zero-column table */
-				if (nfields == 0)
-				{
-					appendPQExpBufferStr(insertStmt, "DEFAULT VALUES;\n");
-				}
-				else
+			/* corner case for zero-column table */
+			if (nfields == 0)
+			{
+				appendPQExpBufferStr(insertStmt, "DEFAULT VALUES;\n");
+			}
+			else
+			{
+				/* append the list of column names if required */
+				if (dopt->column_inserts)
 				{
-					/* append the list of column names if required */
-					if (dopt->column_inserts)
+					appendPQExpBufferChar(insertStmt, '(');
+					for (int field = 0; field < nfields; field++)
 					{
-						appendPQExpBufferChar(insertStmt, '(');
-						for (field = 0; field < nfields; field++)
-						{
-							if (field > 0)
-								appendPQExpBufferStr(insertStmt, ", ");
-							appendPQExpBufferStr(insertStmt,
-												 fmtId(PQfname(res, field)));
-						}
-						appendPQExpBufferStr(insertStmt, ") ");
+						if (field > 0)
+							appendPQExpBufferStr(insertStmt, ", ");
+						appendPQExpBufferStr(insertStmt,
+											 fmtId(PQfname(res, field)));
 					}
+					appendPQExpBufferStr(insertStmt, ") ");
+				}
 
-					if (tbinfo->needs_override)
-						appendPQExpBufferStr(insertStmt, "OVERRIDING SYSTEM VALUE ");
+				if (tbinfo->needs_override)
+					appendPQExpBufferStr(insertStmt, "OVERRIDING SYSTEM VALUE ");
 
-					appendPQExpBufferStr(insertStmt, "VALUES (");
-				}
+				appendPQExpBufferStr(insertStmt, "VALUES");
 			}
+		}
 
-			archputs(insertStmt->data, fout);
+		for (int tuple = 0; tuple < PQntuples(res); tuple++)
+		{
+			/* Write the INSERT if not in the middle of a multi-row INSERT. */
+			if (rows_this_statement == 0)
+				archputs(insertStmt->data, fout);
 
-			/* if it is zero-column table then we're done */
+			/*
+			 * If it is zero-column table then we've aleady written the
+			 * complete statement, which will mean we've disobeyed
+			 * --rows-per-insert when it's set greater than 1.  We do support
+			 * a way to make this multi-row with: SELECT UNION ALL SELECT
+			 * UNION ALL ... but that's non-standard so we should avoid it
+			 * given that using INSERTs is mostly only ever needed for
+			 * cross-database exports.
+			 */
 			if (nfields == 0)
 				continue;
 
-			for (field = 0; field < nfields; field++)
+			/* Emit a row heading */
+			if (rows_per_statement == 1)
+				archputs(" (", fout);
+			else if (rows_this_statement > 0)
+				archputs(",\n\t(", fout);
+			else
+				archputs("\n\t(", fout);
+
+			for (int field = 0; field < nfields; field++)
 			{
 				if (field > 0)
 					archputs(", ", fout);
@@ -2053,10 +2111,19 @@ dumpTableData_insert(Archive *fout, void *dcontext)
 				}
 			}
 
-			if (!dopt->do_nothing)
-				archputs(");\n", fout);
-			else
-				archputs(") ON CONFLICT DO NOTHING;\n", fout);
+			/* Terminate the row ... */
+			archputs(")", fout);
+
+			/* ... and the statement, if the target no. of rows is reached */
+			if (++rows_this_statement >= rows_per_statement)
+			{
+				if (dopt->do_nothing)
+					archputs(" ON CONFLICT DO NOTHING;\n", fout);
+				else
+					archputs(";\n", fout);
+				/* Reset the row counter */
+				rows_this_statement = 0;
+			}
 		}
 
 		if (PQntuples(res) <= 0)
@@ -2067,6 +2134,15 @@ dumpTableData_insert(Archive *fout, void *dcontext)
 		PQclear(res);
 	}
 
+	/* Terminate any statements that didn't make the row count. */
+	if (rows_this_statement > 0)
+	{
+		if (dopt->do_nothing)
+			archputs(" ON CONFLICT DO NOTHING;\n", fout);
+		else
+			archputs(";\n", fout);
+	}
+
 	archputs("\n\n", fout);
 
 	ExecuteSqlStatement(fout, "CLOSE _pg_dump_cursor");

src/bin/pg_dump/t/001_basic.pl

@@ -118,8 +118,8 @@
 
 command_fails_like(
 	[ 'pg_dump', '--on-conflict-do-nothing' ],
-	qr/\Qpg_dump: option --on-conflict-do-nothing requires option --inserts or --column-inserts\E/,
-	'pg_dump: option --on-conflict-do-nothing requires option --inserts or --column-inserts');
+	qr/pg_dump: option --on-conflict-do-nothing requires option --inserts, --rows-per-insert or --column-inserts/,
+	'pg_dump: --on-conflict-do-nothing requires --inserts, --rows-per-insert, --column-inserts');
 
 # pg_dumpall command-line argument checks
 command_fails_like(