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commit    eb91b8ee65721f7e4df218b7a438d9c55e7b972f
Author:   Michael Paquier <michael@paquier.xyz>
Date:     Mon Aug 26 02:14:39 2019 +0000

    Fix error handling of vacuumdb when running out of fds
    
    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


 src/bin/scripts/vacuumdb.c | 20 ++++++++++++++------
 1 file changed, 14 insertions(+), 6 deletions(-)

diff --git a/src/bin/scripts/vacuumdb.c b/src/bin/scripts/vacuumdb.c
index 93728a3a969..a4fe5f86294 100644
--- a/src/bin/scripts/vacuumdb.c
+++ b/src/bin/scripts/vacuumdb.c
@@ -198,12 +198,6 @@ 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);
@@ -437,6 +431,20 @@ 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);
 		}
 	}


[parent: 28d2ce3c7c99]