Fix error handling of vacuumdb when running out of fds

michaelpq · michaelpq · commit 4fca1460099e · 2019-08-26T11:14:33.000+09:00
When trying to use a high number of jobs, vacuumdb has only checked for a maximum number of jobs used, causing confusing failures when running out of file descriptors when the jobs open connections to Postgres. This commit changes the error handling so as we do not check anymore for a maximum number of allowed jobs when parsing the option value with FD_SETSIZE, but check instead if a file descriptor is within the supported range when opening the connections for the jobs so as this is detected at the earliest time possible. Also, improve the error message to give a hint about the number of jobs recommended, using a wording given by the reviewers of the patch. Reported-by: Andres Freund Author: Michael Paquier Reviewed-by: Andres Freund, Álvaro Herrera, Tom Lane Discussion: https://postgr.es/m/20190818001858.ho3ev4z57fqhs7a5@alap3.anarazel.de Backpatch-through: 9.5
diff --git a/src/bin/scripts/vacuumdb.c b/src/bin/scripts/vacuumdb.c
@@ -200,12 +200,6 @@ main(int argc, char *argv[])
 							progname);
 					exit(1);
 				}
-				if (concurrentCons > FD_SETSIZE - 1)
-				{
-					fprintf(stderr, _("%s: too many parallel jobs requested (maximum: %d)\n"),
-							progname, FD_SETSIZE - 1);
-					exit(1);
-				}
 				break;
 			case 2:
 				maintenance_db = pg_strdup(optarg);
@@ -443,6 +437,20 @@ vacuum_one_database(const char *dbname, vacuumingOptions *vacopts,
 		{
 			conn = connectDatabase(dbname, host, port, username, prompt_password,
 								   progname, echo, false, true);
+
+			/*
+			 * Fail and exit immediately if trying to use a socket in an
+			 * unsupported range.  POSIX requires open(2) to use the lowest
+			 * unused file descriptor and the hint given relies on that.
+			 */
+			if (PQsocket(conn) >= FD_SETSIZE)
+			{
+				fprintf(stderr,
+						_("%s: too many jobs for this platform -- try %d"),
+						progname, i);
+				exit(1);
+			}
+
 			init_slot(slots + i, conn);
 		}
 	}
