On Sat, Jun 24, 2017 at 4:05 PM, Thomas Munro <thomas.mu...@enterprisedb.com> wrote: > On Fri, Jun 23, 2017 at 11:48 PM, Thomas Munro > <thomas.mu...@enterprisedb.com> wrote: >> Maybe it needs a better name. > > Ok, how about this: the feature could be called "synchronous replay". > The new column in pg_stat_replication could be called sync_replay > (like the other sync_XXX columns). The GUCs could be called > synchronous replay, synchronous_replay_max_lag and > synchronous_replay_lease_time. The language in log messages could > refer to standbys "joining the synchronous replay set".
Feature hereby renamed that way. It seems a lot more self-explanatory. Please see attached. -- Thomas Munro http://www.enterprisedb.com
synchronous-replay-v1.patch
Description: Binary data
test-synchronous-replay.sh
Description: Bourne shell script
/*
* A simple test program to test performance and visibility with the
* synchronous replay patch.
*
* Each test loop updates a row on the primary, and then optionally checks if
* it can see that change immediately on a standby. If you do this with
* standard async replication, you should occasionally see an assertion fail
* if run with --check (depending on the vaguaries of timing -- I can
* reproduce this very reliably on my system). If you do it with traditional
* sync rep, it becomes a little bit less likely (but it's still reliably
* reproducible on my system). If you do it with traditional sync rep set up,
* and "--synchronous-commit remote_apply" then it should no longer be
* possible to trigger than assertion, but that mode doesn't handle failures.
* If you do it with --synchronous-replay then you should not be able to
* reproduce it, no matter which standby you connect to. If you're using
* --check and the standby gets dropped (perhaps because you
* break/disconnect/pause it etc) you should never see that assertion fail
* (= SELECT running but seeing stale data), instead you should see an error
* when running the SELECT.
*
* Arguments:
*
* --primary <connection-string> how to connect to the primary
* --standby <connection-string> how to connect to the standby to check
* --check check that the update is visible on standby
* --synchronous-replay enable synchronous replay
* --synchronous-commit LEVEL set synchronous_commit to LEVEL
* --two-phase-commit enable two-phase commit
* --loops COUNT how many loops to run through
* --verbose chatter
*/
#include <libpq-fe.h>
#include <assert.h>
#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/time.h>
static double
get_hires_time(void)
{
struct timeval tv;
gettimeofday(&tv, NULL);
return tv.tv_sec + tv.tv_usec / 1000000.0;
}
int
main(int argc, char *argv[])
{
PGconn *primary;
PGconn *standby;
PGresult *result;
int i;
int loops = 10000;
char buffer[1024];
const char *synchronous_commit = "on";
bool synchronous_replay = false;
const char *primary_connstr = "dbname=postgres port=5432";
const char *standby_connstr = "dbname=postgres port=5441";
bool check_applied = false;
bool verbose = false;
bool two_phase_commit = false;
double start_time;
for (i = 1; i != argc; ++i)
{
bool more = (i < argc - 1);
if (strcmp(argv[i], "--verbose") == 0)
verbose = true;
else if (strcmp(argv[i], "--check") == 0)
check_applied = true;
else if (strcmp(argv[i], "--synchronous-commit") == 0 && more)
synchronous_commit = argv[++i];
else if (strcmp(argv[i], "--synchronous-replay") == 0)
synchronous_replay = true;
else if (strcmp(argv[i], "--primary") == 0 && more)
primary_connstr = argv[++i];
else if (strcmp(argv[i], "--standby") == 0 && more)
standby_connstr = argv[++i];
else if (strcmp(argv[i], "--loops") == 0 && more)
loops = atoi(argv[++i]);
else if (strcmp(argv[i], "--two-phase-commit") == 0)
two_phase_commit = true;
else
{
fprintf(stderr, "bad argument\n");
exit(1);
}
}
primary = PQconnectdb(primary_connstr);
assert(PQstatus(primary) == CONNECTION_OK);
standby = PQconnectdb(standby_connstr);
assert(PQstatus(standby) == CONNECTION_OK);
snprintf(buffer, sizeof(buffer), "SET synchronous_commit = %s", synchronous_commit);
result = PQexec(primary, buffer);
assert(PQresultStatus(result) == PGRES_COMMAND_OK);
PQclear(result);
if (synchronous_replay)
{
snprintf(buffer, sizeof(buffer), "SET synchronous_replay = on");
result = PQexec(primary, buffer);
assert(PQresultStatus(result) == PGRES_COMMAND_OK);
PQclear(result);
}
snprintf(buffer, sizeof(buffer), "SET synchronous_commit = %s", synchronous_commit);
result = PQexec(standby, buffer);
assert(PQresultStatus(result) == PGRES_COMMAND_OK);
PQclear(result);
if (synchronous_replay)
{
snprintf(buffer, sizeof(buffer), "SET synchronous_replay = on");
result = PQexec(standby, buffer);
assert(PQresultStatus(result) == PGRES_COMMAND_OK);
PQclear(result);
}
result = PQexec(primary, "CREATE TABLE counter AS SELECT 0 AS n");
assert(PQresultStatus(result) == PGRES_COMMAND_OK ||
strcmp(PQresultErrorField(result, PG_DIAG_SQLSTATE), "42P07") == 0);
PQclear(result);
start_time = get_hires_time();
for (i = 0; i < loops; ++i)
{
if (verbose)
printf("Updating primary...\n");
if (two_phase_commit)
{
result = PQexec(primary, "BEGIN");
assert(PQresultStatus(result) == PGRES_COMMAND_OK);
PQclear(result);
}
snprintf(buffer, sizeof(buffer), "UPDATE counter SET n = %d", i);
result = PQexec(primary, buffer);
assert(PQresultStatus(result) == PGRES_COMMAND_OK);
PQclear(result);
if (two_phase_commit)
{
snprintf(buffer, sizeof(buffer), "PREPARE TRANSACTION 'tx%d'", i);
result = PQexec(primary, buffer);
assert(PQresultStatus(result) == PGRES_COMMAND_OK);
PQclear(result);
snprintf(buffer, sizeof(buffer), "COMMIT PREPARED 'tx%d'", i);
result = PQexec(primary, buffer);
assert(PQresultStatus(result) == PGRES_COMMAND_OK);
PQclear(result);
}
if (check_applied)
{
if (verbose)
printf("Checking standby...\n");
snprintf(buffer, sizeof(buffer), "SELECT n FROM counter");
result = PQexec(standby, buffer);
assert(PQresultStatus(result) == PGRES_TUPLES_OK);
assert(PQntuples(result) == 1);
assert(atoi(PQgetvalue(result, 0, 0)) == i);
PQclear(result);
}
}
printf("%0.3lf TPS\n", loops / (get_hires_time() - start_time));
exit(0);
}
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