From a887c486d5df956de8ac3ee5db9b5e1c8bbe9fd1 Mon Sep 17 00:00:00 2001
From: Itagaki Takahiro <itagaki.takahiro@gmail.com>
Date: Tue, 23 Mar 2010 01:29:22 +0000
Subject: [PATCH] Each worker thread will have its own log file in pgbench to
avoid interleaved writes. The first worker still uses "pgbench_log.<pid>" for
the name, but additional workers use "pgbench_log.<pid>.<serial-number>"
instead.
Reported by Greg Smith.
---
contrib/pgbench/pgbench.c | 71 ++-
doc/src/sgml/pgbench.sgml | 1270 +++++++++++++++++++------------------
2 files changed, 681 insertions(+), 660 deletions(-)
diff --git a/contrib/pgbench/pgbench.c b/contrib/pgbench/pgbench.c
index b290b7477b1..47a1493c7aa 100644
--- a/contrib/pgbench/pgbench.c
+++ b/contrib/pgbench/pgbench.c
@@ -4,7 +4,7 @@
* A simple benchmark program for PostgreSQL
* Originally written by Tatsuo Ishii and enhanced by many contributors.
*
- * $PostgreSQL: pgsql/contrib/pgbench/pgbench.c,v 1.97 2010/02/26 02:00:32 momjian Exp $
+ * $PostgreSQL: pgsql/contrib/pgbench/pgbench.c,v 1.98 2010/03/23 01:29:22 itagaki Exp $
* Copyright (c) 2000-2010, PostgreSQL Global Development Group
* ALL RIGHTS RESERVED;
*
@@ -131,11 +131,9 @@ int fillfactor = 100;
#define ntellers 10
#define naccounts 100000
-FILE *LOGFILE = NULL;
-
bool use_log; /* log transaction latencies to a file */
-
-int is_connect; /* establish connection for each transaction */
+bool is_connect; /* establish connection for each transaction */
+int main_pid; /* main process id used in log filename */
char *pghost = "";
char *pgport = "";
@@ -183,6 +181,7 @@ typedef struct
*/
typedef struct
{
+ int tid; /* thread id */
pthread_t thread; /* thread handle */
CState *state; /* array of CState */
int nstate; /* length of state[] */
@@ -741,7 +740,7 @@ clientDone(CState *st, bool ok)
/* return false iff client should be disconnected */
static bool
-doCustom(CState *st, instr_time *conn_time)
+doCustom(CState *st, instr_time *conn_time, FILE *logfile)
{
PGresult *res;
Command **commands;
@@ -778,7 +777,7 @@ top:
/*
* transaction finished: record the time it took in the log
*/
- if (use_log && commands[st->state + 1] == NULL)
+ if (logfile && commands[st->state + 1] == NULL)
{
instr_time now;
instr_time diff;
@@ -791,12 +790,12 @@ top:
#ifndef WIN32
/* This is more than we really ought to know about instr_time */
- fprintf(LOGFILE, "%d %d %.0f %d %ld %ld\n",
+ fprintf(logfile, "%d %d %.0f %d %ld %ld\n",
st->id, st->cnt, usec, st->use_file,
(long) now.tv_sec, (long) now.tv_usec);
#else
/* On Windows, instr_time doesn't provide a timestamp anyway */
- fprintf(LOGFILE, "%d %d %.0f %d 0 0\n",
+ fprintf(logfile, "%d %d %.0f %d 0 0\n",
st->id, st->cnt, usec, st->use_file);
#endif
}
@@ -857,7 +856,7 @@ top:
INSTR_TIME_ACCUM_DIFF(*conn_time, end, start);
}
- if (use_log && st->state == 0)
+ if (logfile && st->state == 0)
INSTR_TIME_SET_CURRENT(st->txn_begin);
if (commands[st->state]->type == SQL_COMMAND)
@@ -1833,7 +1832,7 @@ main(int argc, char **argv)
}
break;
case 'C':
- is_connect = 1;
+ is_connect = true;
break;
case 's':
scale_given = true;
@@ -1955,6 +1954,12 @@ main(int argc, char **argv)
exit(1);
}
+ /*
+ * save main process id in the global variable because process id will be
+ * changed after fork.
+ */
+ main_pid = (int) getpid();
+
if (nclients > 1)
{
state = (CState *) realloc(state, sizeof(CState) * nclients);
@@ -1980,20 +1985,6 @@ main(int argc, char **argv)
}
}
- if (use_log)
- {
- char logpath[64];
-
- snprintf(logpath, 64, "pgbench_log.%d", (int) getpid());
- LOGFILE = fopen(logpath, "w");
-
- if (LOGFILE == NULL)
- {
- fprintf(stderr, "Couldn't open logfile \"%s\": %s", logpath, strerror(errno));
- exit(1);
- }
- }
-
if (debug)
{
if (duration <= 0)
@@ -2111,6 +2102,7 @@ main(int argc, char **argv)
threads = (TState *) malloc(sizeof(TState) * nthreads);
for (i = 0; i < nthreads; i++)
{
+ threads[i].tid = i;
threads[i].state = &state[nclients / nthreads * i];
threads[i].nstate = nclients / nthreads;
INSTR_TIME_SET_CURRENT(threads[i].start_time);
@@ -2159,8 +2151,6 @@ main(int argc, char **argv)
INSTR_TIME_SET_CURRENT(total_time);
INSTR_TIME_SUBTRACT(total_time, start_time);
printResults(ttype, total_xacts, nclients, nthreads, total_time, conn_total_time);
- if (LOGFILE)
- fclose(LOGFILE);
return 0;
}
@@ -2171,6 +2161,7 @@ threadRun(void *arg)
TState *thread = (TState *) arg;
CState *state = thread->state;
TResult *result;
+ FILE *logfile = NULL; /* per-thread log file */
instr_time start,
end;
int nstate = thread->nstate;
@@ -2180,7 +2171,25 @@ threadRun(void *arg)
result = malloc(sizeof(TResult));
INSTR_TIME_SET_ZERO(result->conn_time);
- if (is_connect == 0)
+ /* open log file if requested */
+ if (use_log)
+ {
+ char logpath[64];
+
+ if (thread->tid == 0)
+ snprintf(logpath, sizeof(logpath), "pgbench_log.%d", main_pid);
+ else
+ snprintf(logpath, sizeof(logpath), "pgbench_log.%d.%d", main_pid, thread->tid);
+ logfile = fopen(logpath, "w");
+
+ if (logfile == NULL)
+ {
+ fprintf(stderr, "Couldn't open logfile \"%s\": %s", logpath, strerror(errno));
+ goto done;
+ }
+ }
+
+ if (!is_connect)
{
/* make connections to the database */
for (i = 0; i < nstate; i++)
@@ -2202,7 +2211,7 @@ threadRun(void *arg)
int prev_ecnt = st->ecnt;
st->use_file = getrand(0, num_files - 1);
- if (!doCustom(st, &result->conn_time))
+ if (!doCustom(st, &result->conn_time, logfile))
remains--; /* I've aborted */
if (st->ecnt > prev_ecnt && commands[st->state]->type == META_COMMAND)
@@ -2304,7 +2313,7 @@ threadRun(void *arg)
if (st->con && (FD_ISSET(PQsocket(st->con), &input_mask)
|| commands[st->state]->type == META_COMMAND))
{
- if (!doCustom(st, &result->conn_time))
+ if (!doCustom(st, &result->conn_time, logfile))
remains--; /* I've aborted */
}
@@ -2326,6 +2335,8 @@ done:
result->xacts += state[i].cnt;
INSTR_TIME_SET_CURRENT(end);
INSTR_TIME_ACCUM_DIFF(result->conn_time, end, start);
+ if (logfile)
+ fclose(logfile);
return result;
}
diff --git a/doc/src/sgml/pgbench.sgml b/doc/src/sgml/pgbench.sgml
index fc967b59a65..cb94e30c01c 100644
--- a/doc/src/sgml/pgbench.sgml
+++ b/doc/src/sgml/pgbench.sgml
@@ -1,630 +1,640 @@
-<!-- $PostgreSQL: pgsql/doc/src/sgml/pgbench.sgml,v 1.12 2009/12/15 15:59:57 tgl Exp $ -->
-
-<sect1 id="pgbench">
- <title>pgbench</title>
-
- <indexterm zone="pgbench">
- <primary>pgbench</primary>
- </indexterm>
-
- <para>
- <application>pgbench</application> is a simple program for running benchmark
- tests on <productname>PostgreSQL</>. It runs the same sequence of SQL
- commands over and over, possibly in multiple concurrent database sessions,
- and then calculates the average transaction rate (transactions per second).
- By default, <application>pgbench</application> tests a scenario that is
- loosely based on TPC-B, involving five <command>SELECT</>,
- <command>UPDATE</>, and <command>INSERT</> commands per transaction.
- However, it is easy to test other cases by writing your own transaction
- script files.
- </para>
-
- <para>
- Typical output from pgbench looks like:
-
- <programlisting>
-transaction type: TPC-B (sort of)
-scaling factor: 10
-query mode: simple
-number of clients: 10
-number of threads: 1
-number of transactions per client: 1000
-number of transactions actually processed: 10000/10000
-tps = 85.184871 (including connections establishing)
-tps = 85.296346 (excluding connections establishing)
- </programlisting>
-
- The first six lines report some of the most important parameter
- settings. The next line reports the number of transactions completed
- and intended (the latter being just the product of number of clients
- and number of transactions per client); these will be equal unless the run
- failed before completion. The last two lines report the TPS rate,
- figured with and without counting the time to start database sessions.
- </para>
-
- <sect2>
- <title>Overview</title>
-
- <para>
- The default TPC-B-like transaction test requires specific tables to be
- set up beforehand. <application>pgbench</> should be invoked with
- the <literal>-i</> (initialize) option to create and populate these
- tables. (When you are testing a custom script, you don't need this
- step, but will instead need to do whatever setup your test needs.)
- Initialization looks like:
-
- <programlisting>
-pgbench -i <optional> <replaceable>other-options</> </optional> <replaceable>dbname</>
- </programlisting>
-
- where <replaceable>dbname</> is the name of the already-created
- database to test in. (You may also need <literal>-h</>,
- <literal>-p</>, and/or <literal>-U</> options to specify how to
- connect to the database server.)
- </para>
-
- <caution>
- <para>
- <literal>pgbench -i</> creates four tables <structname>pgbench_accounts</>,
- <structname>pgbench_branches</>, <structname>pgbench_history</>, and
- <structname>pgbench_tellers</>,
- destroying any existing tables of these names.
- Be very careful to use another database if you have tables having these
- names!
- </para>
- </caution>
-
- <para>
- At the default <quote>scale factor</> of 1, the tables initially
- contain this many rows:
- </para>
- <programlisting>
-table # of rows
----------------------------------
-pgbench_branches 1
-pgbench_tellers 10
-pgbench_accounts 100000
-pgbench_history 0
- </programlisting>
- <para>
- You can (and, for most purposes, probably should) increase the number
- of rows by using the <literal>-s</> (scale factor) option. The
- <literal>-F</> (fillfactor) option might also be used at this point.
- </para>
-
- <para>
- Once you have done the necessary setup, you can run your benchmark
- with a command that doesn't include <literal>-i</>, that is
-
- <programlisting>
-pgbench <optional> <replaceable>options</> </optional> <replaceable>dbname</>
- </programlisting>
-
- In nearly all cases, you'll need some options to make a useful test.
- The most important options are <literal>-c</> (number of clients),
- <literal>-t</> (number of transactions), <literal>-T</> (time limit),
- and <literal>-f</> (specify a custom script file).
- See below for a full list.
- </para>
-
- <para>
- <xref linkend="pgbench-init-options"> shows options that are used
- during database initialization, while
- <xref linkend="pgbench-run-options"> shows options that are used
- while running benchmarks, and
- <xref linkend="pgbench-common-options"> shows options that are useful
- in both cases.
- </para>
-
- <table id="pgbench-init-options">
- <title><application>pgbench</application> initialization options</title>
- <tgroup cols="2">
- <thead>
- <row>
- <entry>Option</entry>
- <entry>Description</entry>
- </row>
- </thead>
-
- <tbody>
- <row>
- <entry><literal>-i</literal></entry>
- <entry>
- Required to invoke initialization mode.
- </entry>
- </row>
- <row>
- <entry><literal>-s</literal> <replaceable>scale_factor</></entry>
- <entry>
- Multiply the number of rows generated by the scale factor.
- For example, <literal>-s 100</> will create 10,000,000 rows
- in the <structname>pgbench_accounts</> table. Default is 1.
- </entry>
- </row>
- <row>
- <entry><literal>-F</literal> <replaceable>fillfactor</></entry>
- <entry>
- Create the <structname>pgbench_accounts</>,
- <structname>pgbench_tellers</> and
- <structname>pgbench_branches</> tables with the given fillfactor.
- Default is 100.
- </entry>
- </row>
- </tbody>
- </tgroup>
- </table>
-
- <table id="pgbench-run-options">
- <title><application>pgbench</application> benchmarking options</title>
- <tgroup cols="2">
- <thead>
- <row>
- <entry>Option</entry>
- <entry>Description</entry>
- </row>
- </thead>
-
- <tbody>
- <row>
- <entry><literal>-c</literal> <replaceable>clients</></entry>
- <entry>
- Number of clients simulated, that is, number of concurrent database
- sessions. Default is 1.
- </entry>
- </row>
- <row>
- <entry><literal>-j</literal> <replaceable>threads</></entry>
- <entry>
- Number of worker threads within <application>pgbench</application>.
- Using more than one thread can be helpful on multi-CPU machines.
- The number of clients must be a multiple of the number of threads,
- since each thread is given the same number of client sessions to manage.
- Default is 1.
- </entry>
- </row>
- <row>
- <entry><literal>-t</literal> <replaceable>transactions</></entry>
- <entry>
- Number of transactions each client runs. Default is 10.
- </entry>
- </row>
- <row>
- <entry><literal>-T</literal> <replaceable>seconds</></entry>
- <entry>
- Run the test for this many seconds, rather than a fixed number of
- transactions per client. <literal>-t</literal> and
- <literal>-T</literal> are mutually exclusive.
- </entry>
- </row>
- <row>
- <entry><literal>-M</literal> <replaceable>querymode</></entry>
- <entry>
- Protocol to use for submitting queries to the server:
- <itemizedlist>
- <listitem>
- <para><literal>simple</>: use simple query protocol.</para>
- </listitem>
- <listitem>
- <para><literal>extended</>: use extended query protocol.</para>
- </listitem>
- <listitem>
- <para><literal>prepared</>: use extended query protocol with prepared statements.</para>
- </listitem>
- </itemizedlist>
- The default is simple query protocol. (See <xref linkend="protocol">
- for more information.)
- </entry>
- </row>
- <row>
- <entry><literal>-N</literal></entry>
- <entry>
- Do not update <structname>pgbench_tellers</> and
- <structname>pgbench_branches</>.
- This will avoid update contention on these tables, but
- it makes the test case even less like TPC-B.
- </entry>
- </row>
- <row>
- <entry><literal>-S</literal></entry>
- <entry>
- Perform select-only transactions instead of TPC-B-like test.
- </entry>
- </row>
- <row>
- <entry><literal>-f</literal> <replaceable>filename</></entry>
- <entry>
- Read transaction script from <replaceable>filename</>.
- See below for details.
- <literal>-N</literal>, <literal>-S</literal>, and <literal>-f</literal>
- are mutually exclusive.
- </entry>
- </row>
- <row>
- <entry><literal>-n</literal></entry>
- <entry>
- Perform no vacuuming before running the test.
- This option is <emphasis>necessary</>
- if you are running a custom test scenario that does not include
- the standard tables <structname>pgbench_accounts</>,
- <structname>pgbench_branches</>, <structname>pgbench_history</>, and
- <structname>pgbench_tellers</>.
- </entry>
- </row>
- <row>
- <entry><literal>-v</literal></entry>
- <entry>
- Vacuum all four standard tables before running the test.
- With neither <literal>-n</> nor <literal>-v</>, pgbench will vacuum the
- <structname>pgbench_tellers</> and <structname>pgbench_branches</>
- tables, and will truncate <structname>pgbench_history</>.
- </entry>
- </row>
- <row>
- <entry><literal>-D</literal> <replaceable>varname</><literal>=</><replaceable>value</></entry>
- <entry>
- Define a variable for use by a custom script (see below).
- Multiple <literal>-D</> options are allowed.
- </entry>
- </row>
- <row>
- <entry><literal>-C</literal></entry>
- <entry>
- Establish a new connection for each transaction, rather than
- doing it just once per client session.
- This is useful to measure the connection overhead.
- </entry>
- </row>
- <row>
- <entry><literal>-l</literal></entry>
- <entry>
- Write the time taken by each transaction to a logfile.
- See below for details.
- </entry>
- </row>
- <row>
- <entry><literal>-s</literal> <replaceable>scale_factor</></entry>
- <entry>
- Report the specified scale factor in <application>pgbench</>'s
- output. With the built-in tests, this is not necessary; the
- correct scale factor will be detected by counting the number of
- rows in the <structname>pgbench_branches</> table. However, when testing
- custom benchmarks (<literal>-f</> option), the scale factor
- will be reported as 1 unless this option is used.
- </entry>
- </row>
- <row>
- <entry><literal>-d</literal></entry>
- <entry>
- Print debugging output.
- </entry>
- </row>
- </tbody>
- </tgroup>
- </table>
-
- <table id="pgbench-common-options">
- <title><application>pgbench</application> common options</title>
- <tgroup cols="2">
- <thead>
- <row>
- <entry>Option</entry>
- <entry>Description</entry>
- </row>
- </thead>
-
- <tbody>
- <row>
- <entry><literal>-h</literal> <replaceable>hostname</></entry>
- <entry>database server's host</entry>
- </row>
- <row>
- <entry><literal>-p</literal> <replaceable>port</></entry>
- <entry>database server's port</entry>
- </row>
- <row>
- <entry><literal>-U</literal> <replaceable>login</></entry>
- <entry>username to connect as</entry>
- </row>
- </tbody>
- </tgroup>
- </table>
- </sect2>
-
- <sect2>
- <title>What is the <quote>transaction</> actually performed in pgbench?</title>
-
- <para>
- The default transaction script issues seven commands per transaction:
- </para>
-
- <orderedlist>
- <listitem><para><literal>BEGIN;</literal></para></listitem>
- <listitem><para><literal>UPDATE pgbench_accounts SET abalance = abalance + :delta WHERE aid = :aid;</literal></para></listitem>
- <listitem><para><literal>SELECT abalance FROM pgbench_accounts WHERE aid = :aid;</literal></para></listitem>
- <listitem><para><literal>UPDATE pgbench_tellers SET tbalance = tbalance + :delta WHERE tid = :tid;</literal></para></listitem>
- <listitem><para><literal>UPDATE pgbench_branches SET bbalance = bbalance + :delta WHERE bid = :bid;</literal></para></listitem>
- <listitem><para><literal>INSERT INTO pgbench_history (tid, bid, aid, delta, mtime) VALUES (:tid, :bid, :aid, :delta, CURRENT_TIMESTAMP);</literal></para></listitem>
- <listitem><para><literal>END;</literal></para></listitem>
- </orderedlist>
-
- <para>
- If you specify <literal>-N</>, steps 4 and 5 aren't included in the
- transaction. If you specify <literal>-S</>, only the <command>SELECT</> is
- issued.
- </para>
- </sect2>
-
- <sect2>
- <title>Custom Scripts</title>
-
- <para>
- <application>pgbench</application> has support for running custom
- benchmark scenarios by replacing the default transaction script
- (described above) with a transaction script read from a file
- (<literal>-f</literal> option). In this case a <quote>transaction</>
- counts as one execution of a script file. You can even specify
- multiple scripts (multiple <literal>-f</literal> options), in which
- case a random one of the scripts is chosen each time a client session
- starts a new transaction.
- </para>
-
- <para>
- The format of a script file is one SQL command per line; multi-line
- SQL commands are not supported. Empty lines and lines beginning with
- <literal>--</> are ignored. Script file lines can also be
- <quote>meta commands</>, which are interpreted by <application>pgbench</>
- itself, as described below.
- </para>
-
- <para>
- There is a simple variable-substitution facility for script files.
- Variables can be set by the command-line <literal>-D</> option,
- explained above, or by the meta commands explained below.
- In addition to any variables preset by <literal>-D</> command-line options,
- the variable <literal>scale</> is preset to the current scale factor.
- Once set, a variable's
- value can be inserted into a SQL command by writing
- <literal>:</><replaceable>variablename</>. When running more than
- one client session, each session has its own set of variables.
- </para>
-
- <para>
- Script file meta commands begin with a backslash (<literal>\</>).
- Arguments to a meta command are separated by white space.
- These meta commands are supported:
- </para>
-
- <variablelist>
- <varlistentry>
- <term>
- <literal>\set <replaceable>varname</> <replaceable>operand1</> [ <replaceable>operator</> <replaceable>operand2</> ]</literal>
- </term>
-
- <listitem>
- <para>
- Sets variable <replaceable>varname</> to a calculated integer value.
- Each <replaceable>operand</> is either an integer constant or a
- <literal>:</><replaceable>variablename</> reference to a variable
- having an integer value. The <replaceable>operator</> can be
- <literal>+</>, <literal>-</>, <literal>*</>, or <literal>/</>.
- </para>
-
- <para>
- Example:
- <programlisting>
-\set ntellers 10 * :scale
- </programlisting>
- </para>
- </listitem>
- </varlistentry>
-
- <varlistentry>
- <term>
- <literal>\setrandom <replaceable>varname</> <replaceable>min</> <replaceable>max</></literal>
- </term>
-
- <listitem>
- <para>
- Sets variable <replaceable>varname</> to a random integer value
- between the limits <replaceable>min</> and <replaceable>max</> inclusive.
- Each limit can be either an integer constant or a
- <literal>:</><replaceable>variablename</> reference to a variable
- having an integer value.
- </para>
-
- <para>
- Example:
- <programlisting>
-\setrandom aid 1 :naccounts
- </programlisting>
- </para>
- </listitem>
- </varlistentry>
-
- <varlistentry>
- <term>
- <literal>\sleep <replaceable>number</> [ us | ms | s ]</literal>
- </term>
-
- <listitem>
- <para>
- Causes script execution to sleep for the specified duration in
- microseconds (<literal>us</>), milliseconds (<literal>ms</>) or seconds
- (<literal>s</>). If the unit is omitted then seconds are the default.
- <replaceable>number</> can be either an integer constant or a
- <literal>:</><replaceable>variablename</> reference to a variable
- having an integer value.
- </para>
-
- <para>
- Example:
- <programlisting>
-\sleep 10 ms
- </programlisting>
- </para>
- </listitem>
- </varlistentry>
-
- <varlistentry>
- <term>
- <literal>\setshell <replaceable>varname</> <replaceable>command</> [ <replaceable>argument</> ... ]</literal>
- </term>
-
- <listitem>
- <para>
- Sets variable <replaceable>varname</> to the result of the shell command
- <replaceable>command</>. The command must return an integer value
- through its standard output.
- </para>
-
- <para>
- <replaceable>argument</> can be either a text constant or a
- <literal>:</><replaceable>variablename</> reference to a variable of
- any types. If you want to use <replaceable>argument</> starting with
- colons, you need to add an additional colon at the beginning of
- <replaceable>argument</>.
- </para>
-
- <para>
- Example:
- <programlisting>
-\setshell variable_to_be_assigned command literal_argument :variable ::literal_starting_with_colon
- </programlisting>
- </para>
- </listitem>
- </varlistentry>
-
- <varlistentry>
- <term>
- <literal>\shell <replaceable>command</> [ <replaceable>argument</> ... ]</literal>
- </term>
-
- <listitem>
- <para>
- Same as <literal>\setshell</literal>, but the result is ignored.
- </para>
-
- <para>
- Example:
- <programlisting>
-\shell command literal_argument :variable ::literal_starting_with_colon
- </programlisting>
- </para>
- </listitem>
- </varlistentry>
- </variablelist>
-
- <para>
- As an example, the full definition of the built-in TPC-B-like
- transaction is:
-
- <programlisting>
-\set nbranches :scale
-\set ntellers 10 * :scale
-\set naccounts 100000 * :scale
-\setrandom aid 1 :naccounts
-\setrandom bid 1 :nbranches
-\setrandom tid 1 :ntellers
-\setrandom delta -5000 5000
-BEGIN;
-UPDATE pgbench_accounts SET abalance = abalance + :delta WHERE aid = :aid;
-SELECT abalance FROM pgbench_accounts WHERE aid = :aid;
-UPDATE pgbench_tellers SET tbalance = tbalance + :delta WHERE tid = :tid;
-UPDATE pgbench_branches SET bbalance = bbalance + :delta WHERE bid = :bid;
-INSERT INTO pgbench_history (tid, bid, aid, delta, mtime) VALUES (:tid, :bid, :aid, :delta, CURRENT_TIMESTAMP);
-END;
- </programlisting>
-
- This script allows each iteration of the transaction to reference
- different, randomly-chosen rows. (This example also shows why it's
- important for each client session to have its own variables —
- otherwise they'd not be independently touching different rows.)
- </para>
-
- </sect2>
-
- <sect2>
- <title>Per-transaction logging</title>
-
- <para>
- With the <literal>-l</> option, <application>pgbench</> writes the time
- taken by each transaction to a logfile. The logfile will be named
- <filename>pgbench_log.<replaceable>nnn</></filename>, where
- <replaceable>nnn</> is the PID of the pgbench process.
- The format of the log is:
-
- <programlisting>
- <replaceable>client_id</> <replaceable>transaction_no</> <replaceable>time</> <replaceable>file_no</> <replaceable>time_epoch</> <replaceable>time_us</>
- </programlisting>
-
- where <replaceable>time</> is the elapsed transaction time in microseconds,
- <replaceable>file_no</> identifies which script file was used
- (useful when multiple scripts were specified with <literal>-f</>),
- and <replaceable>time_epoch</>/<replaceable>time_us</> are a
- UNIX epoch format timestamp and an offset
- in microseconds (suitable for creating a ISO 8601
- timestamp with fractional seconds) showing when
- the transaction completed.
- </para>
-
- <para>
- Here are example outputs:
- <programlisting>
- 0 199 2241 0 1175850568 995598
- 0 200 2465 0 1175850568 998079
- 0 201 2513 0 1175850569 608
- 0 202 2038 0 1175850569 2663
- </programlisting>
- </para>
- </sect2>
-
- <sect2>
- <title>Good Practices</title>
-
- <para>
- It is very easy to use <application>pgbench</> to produce completely
- meaningless numbers. Here are some guidelines to help you get useful
- results.
- </para>
-
- <para>
- In the first place, <emphasis>never</> believe any test that runs
- for only a few seconds. Use the <literal>-t</> or <literal>-T</> option
- to make the run last at least a few minutes, so as to average out noise.
- In some cases you could need hours to get numbers that are reproducible.
- It's a good idea to try the test run a few times, to find out if your
- numbers are reproducible or not.
- </para>
-
- <para>
- For the default TPC-B-like test scenario, the initialization scale factor
- (<literal>-s</>) should be at least as large as the largest number of
- clients you intend to test (<literal>-c</>); else you'll mostly be
- measuring update contention. There are only <literal>-s</> rows in
- the <structname>pgbench_branches</> table, and every transaction wants to
- update one of them, so <literal>-c</> values in excess of <literal>-s</>
- will undoubtedly result in lots of transactions blocked waiting for
- other transactions.
- </para>
-
- <para>
- The default test scenario is also quite sensitive to how long it's been
- since the tables were initialized: accumulation of dead rows and dead space
- in the tables changes the results. To understand the results you must keep
- track of the total number of updates and when vacuuming happens. If
- autovacuum is enabled it can result in unpredictable changes in measured
- performance.
- </para>
-
- <para>
- A limitation of <application>pgbench</> is that it can itself become
- the bottleneck when trying to test a large number of client sessions.
- This can be alleviated by running <application>pgbench</> on a different
- machine from the database server, although low network latency will be
- essential. It might even be useful to run several <application>pgbench</>
- instances concurrently, on several client machines, against the same
- database server.
- </para>
- </sect2>
-
-</sect1>
+<!-- $PostgreSQL: pgsql/doc/src/sgml/pgbench.sgml,v 1.13 2010/03/23 01:29:22 itagaki Exp $ -->
+
+<sect1 id="pgbench">
+ <title>pgbench</title>
+
+ <indexterm zone="pgbench">
+ <primary>pgbench</primary>
+ </indexterm>
+
+ <para>
+ <application>pgbench</application> is a simple program for running benchmark
+ tests on <productname>PostgreSQL</>. It runs the same sequence of SQL
+ commands over and over, possibly in multiple concurrent database sessions,
+ and then calculates the average transaction rate (transactions per second).
+ By default, <application>pgbench</application> tests a scenario that is
+ loosely based on TPC-B, involving five <command>SELECT</>,
+ <command>UPDATE</>, and <command>INSERT</> commands per transaction.
+ However, it is easy to test other cases by writing your own transaction
+ script files.
+ </para>
+
+ <para>
+ Typical output from pgbench looks like:
+
+ <programlisting>
+transaction type: TPC-B (sort of)
+scaling factor: 10
+query mode: simple
+number of clients: 10
+number of threads: 1
+number of transactions per client: 1000
+number of transactions actually processed: 10000/10000
+tps = 85.184871 (including connections establishing)
+tps = 85.296346 (excluding connections establishing)
+ </programlisting>
+
+ The first six lines report some of the most important parameter
+ settings. The next line reports the number of transactions completed
+ and intended (the latter being just the product of number of clients
+ and number of transactions per client); these will be equal unless the run
+ failed before completion. The last two lines report the TPS rate,
+ figured with and without counting the time to start database sessions.
+ </para>
+
+ <sect2>
+ <title>Overview</title>
+
+ <para>
+ The default TPC-B-like transaction test requires specific tables to be
+ set up beforehand. <application>pgbench</> should be invoked with
+ the <literal>-i</> (initialize) option to create and populate these
+ tables. (When you are testing a custom script, you don't need this
+ step, but will instead need to do whatever setup your test needs.)
+ Initialization looks like:
+
+ <programlisting>
+pgbench -i <optional> <replaceable>other-options</> </optional> <replaceable>dbname</>
+ </programlisting>
+
+ where <replaceable>dbname</> is the name of the already-created
+ database to test in. (You may also need <literal>-h</>,
+ <literal>-p</>, and/or <literal>-U</> options to specify how to
+ connect to the database server.)
+ </para>
+
+ <caution>
+ <para>
+ <literal>pgbench -i</> creates four tables <structname>pgbench_accounts</>,
+ <structname>pgbench_branches</>, <structname>pgbench_history</>, and
+ <structname>pgbench_tellers</>,
+ destroying any existing tables of these names.
+ Be very careful to use another database if you have tables having these
+ names!
+ </para>
+ </caution>
+
+ <para>
+ At the default <quote>scale factor</> of 1, the tables initially
+ contain this many rows:
+ </para>
+ <programlisting>
+table # of rows
+---------------------------------
+pgbench_branches 1
+pgbench_tellers 10
+pgbench_accounts 100000
+pgbench_history 0
+ </programlisting>
+ <para>
+ You can (and, for most purposes, probably should) increase the number
+ of rows by using the <literal>-s</> (scale factor) option. The
+ <literal>-F</> (fillfactor) option might also be used at this point.
+ </para>
+
+ <para>
+ Once you have done the necessary setup, you can run your benchmark
+ with a command that doesn't include <literal>-i</>, that is
+
+ <programlisting>
+pgbench <optional> <replaceable>options</> </optional> <replaceable>dbname</>
+ </programlisting>
+
+ In nearly all cases, you'll need some options to make a useful test.
+ The most important options are <literal>-c</> (number of clients),
+ <literal>-t</> (number of transactions), <literal>-T</> (time limit),
+ and <literal>-f</> (specify a custom script file).
+ See below for a full list.
+ </para>
+
+ <para>
+ <xref linkend="pgbench-init-options"> shows options that are used
+ during database initialization, while
+ <xref linkend="pgbench-run-options"> shows options that are used
+ while running benchmarks, and
+ <xref linkend="pgbench-common-options"> shows options that are useful
+ in both cases.
+ </para>
+
+ <table id="pgbench-init-options">
+ <title><application>pgbench</application> initialization options</title>
+ <tgroup cols="2">
+ <thead>
+ <row>
+ <entry>Option</entry>
+ <entry>Description</entry>
+ </row>
+ </thead>
+
+ <tbody>
+ <row>
+ <entry><literal>-i</literal></entry>
+ <entry>
+ Required to invoke initialization mode.
+ </entry>
+ </row>
+ <row>
+ <entry><literal>-s</literal> <replaceable>scale_factor</></entry>
+ <entry>
+ Multiply the number of rows generated by the scale factor.
+ For example, <literal>-s 100</> will create 10,000,000 rows
+ in the <structname>pgbench_accounts</> table. Default is 1.
+ </entry>
+ </row>
+ <row>
+ <entry><literal>-F</literal> <replaceable>fillfactor</></entry>
+ <entry>
+ Create the <structname>pgbench_accounts</>,
+ <structname>pgbench_tellers</> and
+ <structname>pgbench_branches</> tables with the given fillfactor.
+ Default is 100.
+ </entry>
+ </row>
+ </tbody>
+ </tgroup>
+ </table>
+
+ <table id="pgbench-run-options">
+ <title><application>pgbench</application> benchmarking options</title>
+ <tgroup cols="2">
+ <thead>
+ <row>
+ <entry>Option</entry>
+ <entry>Description</entry>
+ </row>
+ </thead>
+
+ <tbody>
+ <row>
+ <entry><literal>-c</literal> <replaceable>clients</></entry>
+ <entry>
+ Number of clients simulated, that is, number of concurrent database
+ sessions. Default is 1.
+ </entry>
+ </row>
+ <row>
+ <entry><literal>-j</literal> <replaceable>threads</></entry>
+ <entry>
+ Number of worker threads within <application>pgbench</application>.
+ Using more than one thread can be helpful on multi-CPU machines.
+ The number of clients must be a multiple of the number of threads,
+ since each thread is given the same number of client sessions to manage.
+ Default is 1.
+ </entry>
+ </row>
+ <row>
+ <entry><literal>-t</literal> <replaceable>transactions</></entry>
+ <entry>
+ Number of transactions each client runs. Default is 10.
+ </entry>
+ </row>
+ <row>
+ <entry><literal>-T</literal> <replaceable>seconds</></entry>
+ <entry>
+ Run the test for this many seconds, rather than a fixed number of
+ transactions per client. <literal>-t</literal> and
+ <literal>-T</literal> are mutually exclusive.
+ </entry>
+ </row>
+ <row>
+ <entry><literal>-M</literal> <replaceable>querymode</></entry>
+ <entry>
+ Protocol to use for submitting queries to the server:
+ <itemizedlist>
+ <listitem>
+ <para><literal>simple</>: use simple query protocol.</para>
+ </listitem>
+ <listitem>
+ <para><literal>extended</>: use extended query protocol.</para>
+ </listitem>
+ <listitem>
+ <para><literal>prepared</>: use extended query protocol with prepared statements.</para>
+ </listitem>
+ </itemizedlist>
+ The default is simple query protocol. (See <xref linkend="protocol">
+ for more information.)
+ </entry>
+ </row>
+ <row>
+ <entry><literal>-N</literal></entry>
+ <entry>
+ Do not update <structname>pgbench_tellers</> and
+ <structname>pgbench_branches</>.
+ This will avoid update contention on these tables, but
+ it makes the test case even less like TPC-B.
+ </entry>
+ </row>
+ <row>
+ <entry><literal>-S</literal></entry>
+ <entry>
+ Perform select-only transactions instead of TPC-B-like test.
+ </entry>
+ </row>
+ <row>
+ <entry><literal>-f</literal> <replaceable>filename</></entry>
+ <entry>
+ Read transaction script from <replaceable>filename</>.
+ See below for details.
+ <literal>-N</literal>, <literal>-S</literal>, and <literal>-f</literal>
+ are mutually exclusive.
+ </entry>
+ </row>
+ <row>
+ <entry><literal>-n</literal></entry>
+ <entry>
+ Perform no vacuuming before running the test.
+ This option is <emphasis>necessary</>
+ if you are running a custom test scenario that does not include
+ the standard tables <structname>pgbench_accounts</>,
+ <structname>pgbench_branches</>, <structname>pgbench_history</>, and
+ <structname>pgbench_tellers</>.
+ </entry>
+ </row>
+ <row>
+ <entry><literal>-v</literal></entry>
+ <entry>
+ Vacuum all four standard tables before running the test.
+ With neither <literal>-n</> nor <literal>-v</>, pgbench will vacuum the
+ <structname>pgbench_tellers</> and <structname>pgbench_branches</>
+ tables, and will truncate <structname>pgbench_history</>.
+ </entry>
+ </row>
+ <row>
+ <entry><literal>-D</literal> <replaceable>varname</><literal>=</><replaceable>value</></entry>
+ <entry>
+ Define a variable for use by a custom script (see below).
+ Multiple <literal>-D</> options are allowed.
+ </entry>
+ </row>
+ <row>
+ <entry><literal>-C</literal></entry>
+ <entry>
+ Establish a new connection for each transaction, rather than
+ doing it just once per client session.
+ This is useful to measure the connection overhead.
+ </entry>
+ </row>
+ <row>
+ <entry><literal>-l</literal></entry>
+ <entry>
+ Write the time taken by each transaction to a logfile.
+ See below for details.
+ </entry>
+ </row>
+ <row>
+ <entry><literal>-s</literal> <replaceable>scale_factor</></entry>
+ <entry>
+ Report the specified scale factor in <application>pgbench</>'s
+ output. With the built-in tests, this is not necessary; the
+ correct scale factor will be detected by counting the number of
+ rows in the <structname>pgbench_branches</> table. However, when testing
+ custom benchmarks (<literal>-f</> option), the scale factor
+ will be reported as 1 unless this option is used.
+ </entry>
+ </row>
+ <row>
+ <entry><literal>-d</literal></entry>
+ <entry>
+ Print debugging output.
+ </entry>
+ </row>
+ </tbody>
+ </tgroup>
+ </table>
+
+ <table id="pgbench-common-options">
+ <title><application>pgbench</application> common options</title>
+ <tgroup cols="2">
+ <thead>
+ <row>
+ <entry>Option</entry>
+ <entry>Description</entry>
+ </row>
+ </thead>
+
+ <tbody>
+ <row>
+ <entry><literal>-h</literal> <replaceable>hostname</></entry>
+ <entry>database server's host</entry>
+ </row>
+ <row>
+ <entry><literal>-p</literal> <replaceable>port</></entry>
+ <entry>database server's port</entry>
+ </row>
+ <row>
+ <entry><literal>-U</literal> <replaceable>login</></entry>
+ <entry>username to connect as</entry>
+ </row>
+ </tbody>
+ </tgroup>
+ </table>
+ </sect2>
+
+ <sect2>
+ <title>What is the <quote>transaction</> actually performed in pgbench?</title>
+
+ <para>
+ The default transaction script issues seven commands per transaction:
+ </para>
+
+ <orderedlist>
+ <listitem><para><literal>BEGIN;</literal></para></listitem>
+ <listitem><para><literal>UPDATE pgbench_accounts SET abalance = abalance + :delta WHERE aid = :aid;</literal></para></listitem>
+ <listitem><para><literal>SELECT abalance FROM pgbench_accounts WHERE aid = :aid;</literal></para></listitem>
+ <listitem><para><literal>UPDATE pgbench_tellers SET tbalance = tbalance + :delta WHERE tid = :tid;</literal></para></listitem>
+ <listitem><para><literal>UPDATE pgbench_branches SET bbalance = bbalance + :delta WHERE bid = :bid;</literal></para></listitem>
+ <listitem><para><literal>INSERT INTO pgbench_history (tid, bid, aid, delta, mtime) VALUES (:tid, :bid, :aid, :delta, CURRENT_TIMESTAMP);</literal></para></listitem>
+ <listitem><para><literal>END;</literal></para></listitem>
+ </orderedlist>
+
+ <para>
+ If you specify <literal>-N</>, steps 4 and 5 aren't included in the
+ transaction. If you specify <literal>-S</>, only the <command>SELECT</> is
+ issued.
+ </para>
+ </sect2>
+
+ <sect2>
+ <title>Custom Scripts</title>
+
+ <para>
+ <application>pgbench</application> has support for running custom
+ benchmark scenarios by replacing the default transaction script
+ (described above) with a transaction script read from a file
+ (<literal>-f</literal> option). In this case a <quote>transaction</>
+ counts as one execution of a script file. You can even specify
+ multiple scripts (multiple <literal>-f</literal> options), in which
+ case a random one of the scripts is chosen each time a client session
+ starts a new transaction.
+ </para>
+
+ <para>
+ The format of a script file is one SQL command per line; multi-line
+ SQL commands are not supported. Empty lines and lines beginning with
+ <literal>--</> are ignored. Script file lines can also be
+ <quote>meta commands</>, which are interpreted by <application>pgbench</>
+ itself, as described below.
+ </para>
+
+ <para>
+ There is a simple variable-substitution facility for script files.
+ Variables can be set by the command-line <literal>-D</> option,
+ explained above, or by the meta commands explained below.
+ In addition to any variables preset by <literal>-D</> command-line options,
+ the variable <literal>scale</> is preset to the current scale factor.
+ Once set, a variable's
+ value can be inserted into a SQL command by writing
+ <literal>:</><replaceable>variablename</>. When running more than
+ one client session, each session has its own set of variables.
+ </para>
+
+ <para>
+ Script file meta commands begin with a backslash (<literal>\</>).
+ Arguments to a meta command are separated by white space.
+ These meta commands are supported:
+ </para>
+
+ <variablelist>
+ <varlistentry>
+ <term>
+ <literal>\set <replaceable>varname</> <replaceable>operand1</> [ <replaceable>operator</> <replaceable>operand2</> ]</literal>
+ </term>
+
+ <listitem>
+ <para>
+ Sets variable <replaceable>varname</> to a calculated integer value.
+ Each <replaceable>operand</> is either an integer constant or a
+ <literal>:</><replaceable>variablename</> reference to a variable
+ having an integer value. The <replaceable>operator</> can be
+ <literal>+</>, <literal>-</>, <literal>*</>, or <literal>/</>.
+ </para>
+
+ <para>
+ Example:
+ <programlisting>
+\set ntellers 10 * :scale
+ </programlisting>
+ </para>
+ </listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term>
+ <literal>\setrandom <replaceable>varname</> <replaceable>min</> <replaceable>max</></literal>
+ </term>
+
+ <listitem>
+ <para>
+ Sets variable <replaceable>varname</> to a random integer value
+ between the limits <replaceable>min</> and <replaceable>max</> inclusive.
+ Each limit can be either an integer constant or a
+ <literal>:</><replaceable>variablename</> reference to a variable
+ having an integer value.
+ </para>
+
+ <para>
+ Example:
+ <programlisting>
+\setrandom aid 1 :naccounts
+ </programlisting>
+ </para>
+ </listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term>
+ <literal>\sleep <replaceable>number</> [ us | ms | s ]</literal>
+ </term>
+
+ <listitem>
+ <para>
+ Causes script execution to sleep for the specified duration in
+ microseconds (<literal>us</>), milliseconds (<literal>ms</>) or seconds
+ (<literal>s</>). If the unit is omitted then seconds are the default.
+ <replaceable>number</> can be either an integer constant or a
+ <literal>:</><replaceable>variablename</> reference to a variable
+ having an integer value.
+ </para>
+
+ <para>
+ Example:
+ <programlisting>
+\sleep 10 ms
+ </programlisting>
+ </para>
+ </listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term>
+ <literal>\setshell <replaceable>varname</> <replaceable>command</> [ <replaceable>argument</> ... ]</literal>
+ </term>
+
+ <listitem>
+ <para>
+ Sets variable <replaceable>varname</> to the result of the shell command
+ <replaceable>command</>. The command must return an integer value
+ through its standard output.
+ </para>
+
+ <para>
+ <replaceable>argument</> can be either a text constant or a
+ <literal>:</><replaceable>variablename</> reference to a variable of
+ any types. If you want to use <replaceable>argument</> starting with
+ colons, you need to add an additional colon at the beginning of
+ <replaceable>argument</>.
+ </para>
+
+ <para>
+ Example:
+ <programlisting>
+\setshell variable_to_be_assigned command literal_argument :variable ::literal_starting_with_colon
+ </programlisting>
+ </para>
+ </listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term>
+ <literal>\shell <replaceable>command</> [ <replaceable>argument</> ... ]</literal>
+ </term>
+
+ <listitem>
+ <para>
+ Same as <literal>\setshell</literal>, but the result is ignored.
+ </para>
+
+ <para>
+ Example:
+ <programlisting>
+\shell command literal_argument :variable ::literal_starting_with_colon
+ </programlisting>
+ </para>
+ </listitem>
+ </varlistentry>
+ </variablelist>
+
+ <para>
+ As an example, the full definition of the built-in TPC-B-like
+ transaction is:
+
+ <programlisting>
+\set nbranches :scale
+\set ntellers 10 * :scale
+\set naccounts 100000 * :scale
+\setrandom aid 1 :naccounts
+\setrandom bid 1 :nbranches
+\setrandom tid 1 :ntellers
+\setrandom delta -5000 5000
+BEGIN;
+UPDATE pgbench_accounts SET abalance = abalance + :delta WHERE aid = :aid;
+SELECT abalance FROM pgbench_accounts WHERE aid = :aid;
+UPDATE pgbench_tellers SET tbalance = tbalance + :delta WHERE tid = :tid;
+UPDATE pgbench_branches SET bbalance = bbalance + :delta WHERE bid = :bid;
+INSERT INTO pgbench_history (tid, bid, aid, delta, mtime) VALUES (:tid, :bid, :aid, :delta, CURRENT_TIMESTAMP);
+END;
+ </programlisting>
+
+ This script allows each iteration of the transaction to reference
+ different, randomly-chosen rows. (This example also shows why it's
+ important for each client session to have its own variables —
+ otherwise they'd not be independently touching different rows.)
+ </para>
+
+ </sect2>
+
+ <sect2>
+ <title>Per-transaction logging</title>
+
+ <para>
+ With the <literal>-l</> option, <application>pgbench</> writes the time
+ taken by each transaction to a logfile. The logfile will be named
+ <filename>pgbench_log.<replaceable>nnn</></filename>, where
+ <replaceable>nnn</> is the PID of the pgbench process.
+ If the <literal>-j</> option is 2 or higher, creating multiple worker
+ threads, each will have its own log file. The first worker will use the
+ the same name for its log file as in the standard single worker case.
+ The additional log files for the other workers will be named
+ <filename>pgbench_log.<replaceable>nnn</>.<replaceable>mmm</></filename>,
+ where <replaceable>mmm</> is a sequential number for each worker starting
+ with 1.
+ </para>
+
+ <para>
+ The format of the log is:
+
+ <programlisting>
+ <replaceable>client_id</> <replaceable>transaction_no</> <replaceable>time</> <replaceable>file_no</> <replaceable>time_epoch</> <replaceable>time_us</>
+ </programlisting>
+
+ where <replaceable>time</> is the elapsed transaction time in microseconds,
+ <replaceable>file_no</> identifies which script file was used
+ (useful when multiple scripts were specified with <literal>-f</>),
+ and <replaceable>time_epoch</>/<replaceable>time_us</> are a
+ UNIX epoch format timestamp and an offset
+ in microseconds (suitable for creating a ISO 8601
+ timestamp with fractional seconds) showing when
+ the transaction completed.
+ </para>
+
+ <para>
+ Here are example outputs:
+ <programlisting>
+ 0 199 2241 0 1175850568 995598
+ 0 200 2465 0 1175850568 998079
+ 0 201 2513 0 1175850569 608
+ 0 202 2038 0 1175850569 2663
+ </programlisting>
+ </para>
+ </sect2>
+
+ <sect2>
+ <title>Good Practices</title>
+
+ <para>
+ It is very easy to use <application>pgbench</> to produce completely
+ meaningless numbers. Here are some guidelines to help you get useful
+ results.
+ </para>
+
+ <para>
+ In the first place, <emphasis>never</> believe any test that runs
+ for only a few seconds. Use the <literal>-t</> or <literal>-T</> option
+ to make the run last at least a few minutes, so as to average out noise.
+ In some cases you could need hours to get numbers that are reproducible.
+ It's a good idea to try the test run a few times, to find out if your
+ numbers are reproducible or not.
+ </para>
+
+ <para>
+ For the default TPC-B-like test scenario, the initialization scale factor
+ (<literal>-s</>) should be at least as large as the largest number of
+ clients you intend to test (<literal>-c</>); else you'll mostly be
+ measuring update contention. There are only <literal>-s</> rows in
+ the <structname>pgbench_branches</> table, and every transaction wants to
+ update one of them, so <literal>-c</> values in excess of <literal>-s</>
+ will undoubtedly result in lots of transactions blocked waiting for
+ other transactions.
+ </para>
+
+ <para>
+ The default test scenario is also quite sensitive to how long it's been
+ since the tables were initialized: accumulation of dead rows and dead space
+ in the tables changes the results. To understand the results you must keep
+ track of the total number of updates and when vacuuming happens. If
+ autovacuum is enabled it can result in unpredictable changes in measured
+ performance.
+ </para>
+
+ <para>
+ A limitation of <application>pgbench</> is that it can itself become
+ the bottleneck when trying to test a large number of client sessions.
+ This can be alleviated by running <application>pgbench</> on a different
+ machine from the database server, although low network latency will be
+ essential. It might even be useful to run several <application>pgbench</>
+ instances concurrently, on several client machines, against the same
+ database server.
+ </para>
+ </sect2>
+
+</sect1>
--
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