pgreplay - Online in the Cloud

PROGRAM:

NAME

pgreplay - PostgreSQL log file replayer for performance tests

SYNOPSIS

pgreplay [parse options] [replay options] [-d level] [infile]
pgreplay -f [parse options] [-o outfile] [-d level] [infile]
pgreplay -r [replay options] [-d level] [infile]

DESCRIPTION

pgreplay reads a PostgreSQL log file (not a WAL file), extracts the SQL statements and
executes them in the same order and relative time against a PostgreSQL database cluster.
A final report gives you a useful statistical analysis of your workload and its execution.

In the first form, the log file infile is replayed at the time it is read.

With the -f option, pgreplay will not execute the statements, but write them to a ‘replay
file’ outfile that can be replayed with the third form.

With the -r option, pgreplay will execute the statements in the replay file infile that
was created by the second form.

If the execution of statements gets behind schedule, warning messages are issued that
indicate that the server cannot handle the load in a timely fashion. The idea is to
replay a real-world database workload as exactly as possible.

To create a log file that can be parsed by pgreplay, you need to set the following
parameters in postgresql.conf:

log_min_messages=error (or more)
log_min_error_statement=log (or more)
log_connections=on
log_disconnections=on
log_line_prefix='%m|%u|%d|%c|' (if you don't use CSV logging)
log_statement='all'
lc_messages must be set to English (encoding does not matter)
bytea_output=escape (from version 9.0 on, only if you want to replay the log on 8.4
or earlier)

The database cluster against which you replay the SQL statements must be a clone of the
database cluster that generated the logs from the time immediately before the logs were
generated.

pgreplay is useful for performance tests, particularly in the following situations:

* You want to compare the performance of your PostgreSQL application on different
hardware or different operating systems.

* You want to upgrade your database and want to make sure that the new database version
does not suffer from performance regressions that affect you.

Moreover, pgreplay can give you some feeling as to how your application might scale by
allowing you to try to replay the workload at a higher speed. Be warned, though, that 500
users working at double speed is not really the same as 1000 users working at normal
speed.

OPTIONS

Parse options:
-c Specifies that the log file is in 'csvlog' format (highly recommended) and not in
'stderr' format.

-b timestamp
Only log entries greater or equal to that timestamp will be parsed. The format is
YYYY-MM-DD HH:MM:SS.FFF like in the log file. An optional time zone part will be
ignored.

-e timestamp
Only log entries less or equal to that timestamp will be parsed. The format is
YYYY-MM-DD HH:MM:SS.FFF like in the log file. An optional time zone part will be
ignored.

-q Specifies that a backslash in a simple string literal will escape the following
single quote. This depends on configuration options like
standard_conforming_strings and is the default for server version 9.0 and less.

Replay options:
-h hostname
Host name where the target database cluster is running (or directory where the UNIX
socket can be found). Defaults to local connections.
This works just like the -h option of psql.

-p port
TCP port where the target database cluster can be reached.

-W password
By default, pgreplay assumes that the target database cluster is configured for
trust authentication. With the -W option you can specify a password that will be
used for all users in the cluster.

-s factor
Speed factor for replay, by default 1. This can be any valid positive floating
point number. A factor less than 1 will replay the workload in ‘slow motion’, while
a factor greater than 1 means ‘fast forward’.

-E encoding
Specifies the encoding of the log file, which will be used as client encoding
during replay. If it is omitted, your default client encoding will be used.

-j If all connections are idle, jump ahead to the next request instead of sleeping.
This will speed up replay. Execution delays will still be reported correctly, but
replay statistics will not contain the idle time.

Output options:
-o outfile
specifies the replay file where the statements will be written for later replay.

Debug options:
-d level
Specifies the trace level (between 1 and 3). Increasing levels will produce more
detailed information about what pgreplay is doing.

-v Prints the program version and exits.

ENVIRONMENT

PGHOST Specifies the default value for the -h option.

PGPORT Specifies the default value for the -p option.

PGCLIENTENCODING
Specifies the default value for the -E option.

LIMITATIONS

pgreplay can only replay what is logged by PostgreSQL. This leads to some limitations:

* COPY statements will not be replayed, because the copy data are not logged.

* Fast-path API function calls are not logged and will not be replayed. Unfortunately,
this includes the Large Object API.

* Since the log file is always in the server encoding (which you can specify with the -E
switch of pgreplay), all SET client_encoding statements will be ignored.

* Since the preparation time of prepared statements is not logged (unless
log_min_messages is debug2 or more), these statements will be prepared immediately
before they are first executed during replay.

* Because the log file contains only text, query parameters and return values will
always be in text and never in binary format. If you use binary mode to, say, transfer
large binary data, pgreplay can cause significantly more network traffic than the
original run.

* Sometimes, if a connection takes longer to complete, the session ID unexpectedly
changes in the PostgreSQL log file. This causes pgreplay to treat the session as two
different ones, resulting in an additional connection. This is arguably a bug in
PostgreSQL.

Use pgreplay online using onworks.net services