On Wed, May 22, 2013 at 11:11 PM, Andres Freund <and...@2ndquadrant.com> wrote: > Make that actually having acquired an xid. We skip a large part of the > work if a transaction doesn't yet have one afair. I don't think the mere > presence of 600 idle connections without an xid in contrast to just > having max_connection at 600 should actually make a difference in the > cost of acquiring a snapshot?
Attached is a slightly updated version of the patch I'm using for testing, and an updated version of the pg_cxn source that I'm using to open lotsa connections. With this version, I can do this: ./pg_cxn -n 600 -c BEGIN -c 'SELECT txid_current()' ...which I think is sufficient to make sure all those transactions have XIDs. Then I reran the "depend" test case (create a schema with 1000,000 functions and then drop the schema with CASCADE) that I mentioned in my original posting. Here are the results: MVCC Off: Create 8685.662 ms, Drop 9973.233 ms MVCC On: Create 7931.039 ms, Drop 10189.189 ms MVCC Off: Create 7810.084 ms, Drop 9594.580 ms MVCC On: Create 8854.577 ms, Drop 10240.024 ms OK, let's try the rebuild-the-relcache test using the same pg_cxn scenario (600 transactions that have started a transaction and selected txid_current()). [rhaas ~]$ time for s in `seq 1 1000`; do rm -f pgdata/global/pg_internal.init && psql -c 'SELECT 2+2' >/dev/null; done MVCC catalog access on: real 0m11.006s user 0m2.746s sys 0m2.664s MVCC catalog access off: real 0m10.583s user 0m2.745s sys 0m2.661s MVCC catalog access on: real 0m10.646s user 0m2.750s sys 0m2.661s MVCC catalog access off: real 0m10.823s user 0m2.756s sys 0m2.681s -- Robert Haas EnterpriseDB: http://www.enterprisedb.com The Enterprise PostgreSQL Company
mvcc-catalog-access-v2.patch
Description: Binary data
/*
* pg_cxn.c
*/
#include <stdio.h>
#include <stdlib.h>
#include <getopt.h>
#include "libpq-fe.h"
struct cmd_list;
typedef struct cmd_list cmd_list;
struct cmd_list
{
char *cmd;
cmd_list *next;
};
static void pg_connect(const char *conninfo, cmd_list *);
static cmd_list *add_command(cmd_list *, char *);
static void usage(void);
int
main(int argc, char **argv)
{
int c;
int n = 1;
int optindex;
int i;
const char *conninfo;
cmd_list *cmds;
while ((c = getopt_long(argc, argv, "n:c:", NULL, &optindex)) != -1)
{
switch (c)
{
case 'n':
n = atoi(optarg);
break;
case 'c':
cmds = add_command(cmds, optarg);
break;
default:
usage();
break;
}
}
argv += optind;
argc -= optind;
if (argc > 0)
conninfo = argv[0];
else
conninfo = "";
for (i = 0; i < n; ++i)
pg_connect(conninfo, cmds);
printf("Established %d connections.\n", n);
while (1)
sleep(3600);
return 0;
}
static cmd_list *
add_command(cmd_list *cmds, char *cmd)
{
cmd_list *newnode;
newnode = malloc(sizeof(cmd_list));
if (newnode == NULL)
{
perror("malloc");
exit(1);
}
newnode->cmd = cmd;
newnode->next = cmds;
return newnode;
}
static void
pg_connect(const char *conninfo, cmd_list *cmds)
{
PGconn *conn;
/* Make a connection to the database */
conn = PQconnectdb(conninfo);
/* Check to see that the backend connection was successfully made */
if (PQstatus(conn) != CONNECTION_OK)
{
fprintf(stderr, "%s", PQerrorMessage(conn));
exit(1);
}
/* Execute commands. */
while (cmds != NULL)
{
PGresult *res;
res = PQexec(conn, cmds->cmd);
if (PQresultStatus(res) == PGRES_FATAL_ERROR)
{
fprintf(stderr, "%s", PQresultErrorMessage(res));
exit(1);
}
if (PQresultStatus(res) != PGRES_COMMAND_OK
&& PQresultStatus(res) != PGRES_TUPLES_OK)
{
fprintf(stderr, "unexpected result status: %s\n",
PQresStatus(PQresultStatus(res)));
exit(1);
}
PQclear(res);
cmds = cmds->next;
}
}
static void
usage()
{
fprintf(stderr, "Usage: pg_cxn [OPTION] [CONNECTION-STRING]\n\n"
"Options:\n"
" -n NUM Number of connections to open.\n"
" -c SQL SQL to execute on each connection.\n"
" (You can repeat this option more than once.)\n");
exit(1);
}
-- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
