mirror of https://github.com/zulip/zulip.git
158 lines
6.7 KiB
Markdown
158 lines
6.7 KiB
Markdown
PostgreSQL database details
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=========================
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Starting with Zulip 3.0, Zulip supports using PostgreSQL 10, 11, or 12,
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defaulting to PostgreSQL 12 for new installations.
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Previous versions of Zulip used whatever version of PostgreSQL was
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included with the base operating system (E.g. PostgreSQL 12 on Ubuntu
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Focal, 10 on Ubuntu Bionic, and 9.6 on Ubuntu Xenial). We recommend
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that installations currently using older PostgreSQL releases [upgrade to
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PostgreSQL 12][upgrade-postgresql], as may drop support for older PostgreSQL
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in a future release.
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[upgrade-postgresql]: ../production/upgrade-or-modify.html#upgrading-postgresql
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#### Remote PostgreSQL database
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This is a bit annoying to set up, but you can configure Zulip to use a
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dedicated PostgreSQL server by setting the `REMOTE_POSTGRES_HOST`
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variable in /etc/zulip/settings.py, and configuring PostgreSQL
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certificate authentication (see
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http://www.postgresql.org/docs/9.1/static/ssl-tcp.html and
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http://www.postgresql.org/docs/9.1/static/libpq-ssl.html for
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documentation on how to set this up and deploy the certificates) to
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make the DATABASES configuration in `zproject/computed_settings.py`
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work (or override that configuration).
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If you want to use a remote PostgreSQL database, you should configure
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the information about the connection with the server. You need a user
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called "zulip" in your database server. You can configure these
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options in `/etc/zulip/settings.py` (the below descriptions are from the
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PostgreSQL documentation):
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* `REMOTE_POSTGRES_HOST`: Name or IP address of the remote host
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* `REMOTE_POSTGRES_SSLMODE`: SSL Mode used to connect to the server,
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different options you can use are:
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* disable: I don't care about security, and I don't want to pay the
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overhead of encryption.
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* allow: I don't care about security, but I will pay the overhead of
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encryption if the server insists on it.
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* prefer: I don't care about encryption, but I wish to pay the
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overhead of encryption if the server supports it.
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* require: I want my data to be encrypted, and I accept the
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overhead. I trust that the network will make sure I always connect
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to the server I want.
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* verify-ca: I want my data encrypted, and I accept the overhead. I
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want to be sure that I connect to a server that I trust.
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* verify-full: I want my data encrypted, and I accept the
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overhead. I want to be sure that I connect to a server I trust,
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and that it's the one I specify.
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Then you should specify the password of the user zulip for the
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database in /etc/zulip/zulip-secrets.conf:
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```
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postgres_password = xxxx
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```
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Finally, you can stop your database on the Zulip server via:
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```
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sudo service postgresql stop
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sudo update-rc.d postgresql disable
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```
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In future versions of this feature, we'd like to implement and
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document how to the remote PostgreSQL database server itself
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automatically by using the Zulip install script with a different set
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of Puppet manifests than the all-in-one feature; if you're interested
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in working on this, post to the Zulip development mailing list and we
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can give you some tips.
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#### Debugging PostgreSQL database issues
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When debugging PostgreSQL issues, in addition to the standard `pg_top`
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tool, often it can be useful to use this query:
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```
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SELECT procpid,waiting,query_start,current_query FROM pg_stat_activity ORDER BY procpid;
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```
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which shows the currently running backends and their activity. This is
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similar to the pg_top output, with the added advantage of showing the
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complete query, which can be valuable in debugging.
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To stop a runaway query, you can run `SELECT pg_cancel_backend(pid
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int)` or `SELECT pg_terminate_backend(pid int)` as the 'postgres'
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user. The former cancels the backend's current query and the latter
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terminates the backend process. They are implemented by sending SIGINT
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and SIGTERM to the processes, respectively. We recommend against
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sending a PostgreSQL process SIGKILL. Doing so will cause the database
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to kill all current connections, roll back any pending transactions,
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and enter recovery mode.
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#### Stopping the Zulip PostgreSQL database
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To start or stop PostgreSQL manually, use the pg_ctlcluster command:
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```
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pg_ctlcluster 9.1 [--force] main {start|stop|restart|reload}
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```
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By default, using stop uses "smart" mode, which waits for all clients
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to disconnect before shutting down the database. This can take
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prohibitively long. If you use the --force option with stop,
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pg_ctlcluster will try to use the "fast" mode for shutting
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down. "Fast" mode is described by the manpage thusly:
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With the --force option the "fast" mode is used which rolls back all
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active transactions, disconnects clients immediately and thus shuts
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down cleanly. If that does not work, shutdown is attempted again in
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"immediate" mode, which can leave the cluster in an inconsistent state
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and thus will lead to a recovery run at the next start. If this still
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does not help, the postmaster process is killed. Exits with 0 on
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success, with 2 if the server is not running, and with 1 on other
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failure conditions. This mode should only be used when the machine is
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about to be shut down.
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Many database parameters can be adjusted while the database is
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running. Just modify /etc/postgresql/9.1/main/postgresql.conf and
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issue a reload. The logs will note the change.
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#### Debugging issues starting PostgreSQL
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pg_ctlcluster often doesn't give you any information on why the
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database failed to start. It may tell you to check the logs, but you
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won't find any information there. pg_ctlcluster runs the following
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command underneath when it actually goes to start PostgreSQL:
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```
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/usr/lib/postgresql/9.1/bin/pg_ctl start -D /var/lib/postgresql/9.1/main -s -o \
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'-c config_file="/etc/postgresql/9.1/main/postgresql.conf"'
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```
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Since pg_ctl doesn't redirect stdout or stderr, running the above can
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give you better diagnostic information. However, you might want to
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stop PostgreSQL and restart it using pg_ctlcluster after you've debugged
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with this approach, since it does bypass some of the work that
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pg_ctlcluster does.
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#### PostgreSQL vacuuming alerts
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The `autovac_freeze` PostgreSQL alert from `check_postgres` is
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particularly important. This alert indicates that the age (in terms
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of number of transactions) of the oldest transaction id (XID) is
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getting close to the `autovacuum_freeze_max_age` setting. When the
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oldest XID hits that age, PostgreSQL will force a VACUUM operation,
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which can often lead to sudden downtime until the operation finishes.
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If it did not do this and the age of the oldest XID reached 2 billion,
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transaction id wraparound would occur and there would be data loss.
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To clear the nagios alert, perform a `VACUUM` in each indicated
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database as a database superuser (`postgres`).
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See
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http://www.postgresql.org/docs/9.1/static/routine-vacuuming.html#VACUUM-FOR-WRAPAROUND
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for more details on PostgreSQL vacuuming.
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