Refactor parallelization processing code in src/bin/scripts/

The existing facility of vacuumdb to handle parallel connections into a
given database with an authentication set is moved to a common file in
src/bin/scripts/, named scripts_parallel.c.  This introduces a set of
routines to initialize, wait and terminate a set of connections,
simplifying a bit the code of vacuumdb on the way.  More routines
related to result handling and database connection are moved to
common.c.

The initial plan is to use that for reindexdb, but it could be applied
to other tools like clusterdb.

While on it, clean up a set of variables "progname" which were defined
as routine arguments for error messages.  Since most of the callers have
switched to pg_log_error() and such there is no need for this variable.

Author: Julien Rouhaud
Reviewed-by: Michael Paquier, Álvaro Herrera
Discussion: https://postgr.es/m/CAOBaU_YrnH_Jqo46NhaJ7uRBiWWEcS40VNRQxgFbqYo9kApUsg@mail.gmail.com

Author: michaelpq

src/bin/scripts/Makefile

@@ -28,7 +28,7 @@ createuser: createuser.o common.o $(WIN32RES) | submake-libpq submake-libpgport
 dropdb: dropdb.o common.o $(WIN32RES) | submake-libpq submake-libpgport submake-libpgfeutils
 dropuser: dropuser.o common.o $(WIN32RES) | submake-libpq submake-libpgport submake-libpgfeutils
 clusterdb: clusterdb.o common.o $(WIN32RES) | submake-libpq submake-libpgport submake-libpgfeutils
-vacuumdb: vacuumdb.o common.o $(WIN32RES) | submake-libpq submake-libpgport submake-libpgfeutils
+vacuumdb: vacuumdb.o common.o scripts_parallel.o $(WIN32RES) | submake-libpq submake-libpgport submake-libpgfeutils
 reindexdb: reindexdb.o common.o $(WIN32RES) | submake-libpq submake-libpgport submake-libpgfeutils
 pg_isready: pg_isready.o common.o $(WIN32RES) | submake-libpq submake-libpgport submake-libpgfeutils
 
@@ -50,7 +50,7 @@ uninstall:
 
 clean distclean maintainer-clean:
 	rm -f $(addsuffix $(X), $(PROGRAMS)) $(addsuffix .o, $(PROGRAMS))
-	rm -f common.o $(WIN32RES)
+	rm -f common.o scripts_parallel.o $(WIN32RES)
 	rm -rf tmp_check
 
 check:

src/bin/scripts/clusterdb.c

@@ -206,7 +206,7 @@ cluster_one_database(const char *dbname, bool verbose, const char *table,
 	if (table)
 	{
 		appendPQExpBufferChar(&sql, ' ');
-		appendQualifiedRelation(&sql, table, conn, progname, echo);
+		appendQualifiedRelation(&sql, table, conn, echo);
 	}
 	appendPQExpBufferChar(&sql, ';');
 
@@ -239,7 +239,7 @@ cluster_all_databases(bool verbose, const char *maintenance_db,
 
 	conn = connectMaintenanceDatabase(maintenance_db, host, port, username,
 									  prompt_password, progname, echo);
-	result = executeQuery(conn, "SELECT datname FROM pg_database WHERE datallowconn ORDER BY 1;", progname, echo);
+	result = executeQuery(conn, "SELECT datname FROM pg_database WHERE datallowconn ORDER BY 1;", echo);
 	PQfinish(conn);
 
 	initPQExpBuffer(&connstr);

src/bin/scripts/common.c

@@ -22,6 +22,8 @@
 #include "fe_utils/connect.h"
 #include "fe_utils/string_utils.h"
 
+#define ERRCODE_UNDEFINED_TABLE  "42P01"
+
 
 static PGcancel *volatile cancelConn = NULL;
 bool		CancelRequested = false;
@@ -146,8 +148,7 @@ connectDatabase(const char *dbname, const char *pghost,
 		exit(1);
 	}
 
-	PQclear(executeQuery(conn, ALWAYS_SECURE_SEARCH_PATH_SQL,
-						 progname, echo));
+	PQclear(executeQuery(conn, ALWAYS_SECURE_SEARCH_PATH_SQL, echo));
 
 	return conn;
 }
@@ -178,11 +179,35 @@ connectMaintenanceDatabase(const char *maintenance_db,
 	return conn;
 }
 
+/*
+ * Disconnect the given connection, canceling any statement if one is active.
+ */
+void
+disconnectDatabase(PGconn *conn)
+{
+	char		errbuf[256];
+
+	Assert(conn != NULL);
+
+	if (PQtransactionStatus(conn) == PQTRANS_ACTIVE)
+	{
+		PGcancel   *cancel;
+
+		if ((cancel = PQgetCancel(conn)))
+		{
+			(void) PQcancel(cancel, errbuf, sizeof(errbuf));
+			PQfreeCancel(cancel);
+		}
+	}
+
+	PQfinish(conn);
+}
+
 /*
  * Run a query, return the results, exit program on failure.
  */
 PGresult *
-executeQuery(PGconn *conn, const char *query, const char *progname, bool echo)
+executeQuery(PGconn *conn, const char *query, bool echo)
 {
 	PGresult   *res;
 
@@ -207,8 +232,7 @@ executeQuery(PGconn *conn, const char *query, const char *progname, bool echo)
  * As above for a SQL command (which returns nothing).
  */
 void
-executeCommand(PGconn *conn, const char *query,
-			   const char *progname, bool echo)
+executeCommand(PGconn *conn, const char *query, bool echo)
 {
 	PGresult   *res;
 
@@ -255,6 +279,57 @@ executeMaintenanceCommand(PGconn *conn, const char *query, bool echo)
 	return r;
 }
 
+/*
+ * Consume all the results generated for the given connection until
+ * nothing remains.  If at least one error is encountered, return false.
+ * Note that this will block if the connection is busy.
+ */
+bool
+consumeQueryResult(PGconn *conn)
+{
+	bool		ok = true;
+	PGresult   *result;
+
+	SetCancelConn(conn);
+	while ((result = PQgetResult(conn)) != NULL)
+	{
+		if (!processQueryResult(conn, result))
+			ok = false;
+	}
+	ResetCancelConn();
+	return ok;
+}
+
+/*
+ * Process (and delete) a query result.  Returns true if there's no error,
+ * false otherwise -- but errors about trying to work on a missing relation
+ * are reported and subsequently ignored.
+ */
+bool
+processQueryResult(PGconn *conn, PGresult *result)
+{
+	/*
+	 * If it's an error, report it.  Errors about a missing table are harmless
+	 * so we continue processing; but die for other errors.
+	 */
+	if (PQresultStatus(result) != PGRES_COMMAND_OK)
+	{
+		char	   *sqlState = PQresultErrorField(result, PG_DIAG_SQLSTATE);
+
+		pg_log_error("processing of database \"%s\" failed: %s",
+					 PQdb(conn), PQerrorMessage(conn));
+
+		if (sqlState && strcmp(sqlState, ERRCODE_UNDEFINED_TABLE) != 0)
+		{
+			PQclear(result);
+			return false;
+		}
+	}
+
+	PQclear(result);
+	return true;
+}
+
 
 /*
  * Split TABLE[(COLUMNS)] into TABLE and [(COLUMNS)] portions.  When you
@@ -299,7 +374,7 @@ splitTableColumnsSpec(const char *spec, int encoding,
  */
 void
 appendQualifiedRelation(PQExpBuffer buf, const char *spec,
-						PGconn *conn, const char *progname, bool echo)
+						PGconn *conn, bool echo)
 {
 	char	   *table;
 	const char *columns;
@@ -324,15 +399,15 @@ appendQualifiedRelation(PQExpBuffer buf, const char *spec,
 	appendStringLiteralConn(&sql, table, conn);
 	appendPQExpBufferStr(&sql, "::pg_catalog.regclass;");
 
-	executeCommand(conn, "RESET search_path;", progname, echo);
+	executeCommand(conn, "RESET search_path;", echo);
 
 	/*
 	 * One row is a typical result, as is a nonexistent relation ERROR.
 	 * regclassin() unconditionally accepts all-digits input as an OID; if no
 	 * relation has that OID; this query returns no rows.  Catalog corruption
 	 * might elicit other row counts.
 	 */
-	res = executeQuery(conn, sql.data, progname, echo);
+	res = executeQuery(conn, sql.data, echo);
 	ntups = PQntuples(res);
 	if (ntups != 1)
 	{
@@ -351,8 +426,7 @@ appendQualifiedRelation(PQExpBuffer buf, const char *spec,
 	termPQExpBuffer(&sql);
 	pg_free(table);
 
-	PQclear(executeQuery(conn, ALWAYS_SECURE_SEARCH_PATH_SQL,
-						 progname, echo));
+	PQclear(executeQuery(conn, ALWAYS_SECURE_SEARCH_PATH_SQL, echo));
 }
 
 

src/bin/scripts/common.h

@@ -39,20 +39,24 @@ extern PGconn *connectMaintenanceDatabase(const char *maintenance_db,
 										  const char *pguser, enum trivalue prompt_password,
 										  const char *progname, bool echo);
 
-extern PGresult *executeQuery(PGconn *conn, const char *query,
-							  const char *progname, bool echo);
+extern void disconnectDatabase(PGconn *conn);
 
-extern void executeCommand(PGconn *conn, const char *query,
-						   const char *progname, bool echo);
+extern PGresult *executeQuery(PGconn *conn, const char *query, bool echo);
+
+extern void executeCommand(PGconn *conn, const char *query, bool echo);
 
 extern bool executeMaintenanceCommand(PGconn *conn, const char *query,
 									  bool echo);
 
+extern bool consumeQueryResult(PGconn *conn);
+
+extern bool processQueryResult(PGconn *conn, PGresult *result);
+
 extern void splitTableColumnsSpec(const char *spec, int encoding,
 								  char **table, const char **columns);
 
 extern void appendQualifiedRelation(PQExpBuffer buf, const char *name,
-									PGconn *conn, const char *progname, bool echo);
+									PGconn *conn, bool echo);
 
 extern bool yesno_prompt(const char *question);
 

src/bin/scripts/reindexdb.c

@@ -348,7 +348,7 @@ reindex_one_database(const char *name, const char *dbname, ReindexType type,
 			break;
 		case REINDEX_INDEX:
 		case REINDEX_TABLE:
-			appendQualifiedRelation(&sql, name, conn, progname, echo);
+			appendQualifiedRelation(&sql, name, conn, echo);
 			break;
 		case REINDEX_SCHEMA:
 			appendPQExpBufferStr(&sql, name);
@@ -405,7 +405,7 @@ reindex_all_databases(const char *maintenance_db,
 
 	conn = connectMaintenanceDatabase(maintenance_db, host, port, username,
 									  prompt_password, progname, echo);
-	result = executeQuery(conn, "SELECT datname FROM pg_database WHERE datallowconn ORDER BY 1;", progname, echo);
+	result = executeQuery(conn, "SELECT datname FROM pg_database WHERE datallowconn ORDER BY 1;", echo);
 	PQfinish(conn);
 
 	initPQExpBuffer(&connstr);