Our database servers provide database storage for many of our apps.
- 1 Contact Information
- 2 Description
- 3 Creating a New Postgresql Database
- 4 Troubleshooting and Resolution
- 5 Note about TurboGears and MySQL
Owner: Fedora Infrastructure Team
Contact: #fedora-admin, sysadmin-main, sysadmin-dba group
Servers: db1, db2, db3
Purpose: Provides database connection to many of our apps.
db1 and db2 are our primary database servers. db1 contains the MySQL instance, db2 contains postgresql. Each database server replicates to itself and the other through a dump style backup. In a normal situation, db1 runs only MySQL, not postgresql. While db2 runs only postgresql not MySQL. Which is running on which is defined in the puppet configs, specifically the node manifest for each server (nodes/db1.fedora.phx.redhat.com.pp and nodes/db2.fedora.phx.redhat.com.pp)
db3 is a postgresql server dedicated to koji.
Creating a New Postgresql Database
Creating a new database on our postgresql server isn't hard but there's several steps that should be taken to make the database server as secure as possible.
db2 $ sudo -u postgres createdb -E utf8 NEWDB db2 $ sudo -u postgres createuser -P -E NEWDBUSER Password: <randomly generated password> db2 $ sudo -u postgres psql NEWDB NEWDB=# revoke all on database NEWDB from public; NEWDB=# revoke all on schema public from public; NEWDB=# grant all on schema public to NEWDBUSER; NEWDB=# [grant other permissions to NEWDBUSER as appropriate for your app]
If you're doing this on a postgresql8.3 install (currently just db3), perform the next step as well:
NEWDB=# grant connect on database NEWDB to nagiosuser;
If your application needs to have the NEWDBUSER and password to connect to the database, you probably want to add these to puppet as well. Put the password in the private repo in puppet1. Then use a templatefile to incorporate it into the config file. See fas.pp for an example.
Troubleshooting and Resolution
There are no known outstanding issues with the database itself. Remember that every time either database is restarted, services will have to be restarted (see below).
Some useful queries
What queries are running
This can help you find out what queries are cuurently running on the server::
select datname, procpid, query_start, backend_start, current_query from pg_stat_activity where current_query != '<IDLE>' order by query_start;
This can help you find how many connections to the db server are for each individual database::
select datname, count(datname) from pg_stat_activity group by datname order by count desc;
Seeing how "dirty" a table is
We've added a function from postgres's contrib directory to tell how dirty a table is. By dirty we mean, how many tuples are active, how many have been marked as having old data (and therefore "dead") and how much free space is allocated to the table but not used.
\c fas2 \x select * from pgstattuple('visit_identity'); table_len | 425984 tuple_count | 580 tuple_len | 46977 tuple_percent | 11.03 dead_tuple_count | 68 dead_tuple_len | 5508 dead_tuple_percent | 1.29 free_space | 352420 free_percent | 82.73 \x
Vacuum should clear out dead_tuples. Only a vacuum full, which will lock the table and therefore should be avoided, will clear out free space.
Find out how close we are to having to perform a vacuum of a database (as opposed to individual tables of the db). We should schedule a vacuum when about 50% of the transaction ids have been used (approximately 530,000,000 xids):
select datname, age(datfrozenxid), pow(2, 31) - age(datfrozenxid) as xids_remaining from pg_database order by xids_remaining;
Information on wraparound
If the database server needs to be restarted it should come back on it's own. Otherwise each service on it can be restarted:
service mysqld restart service postgresql restart
Any time postgreql is restarted, koji needs to be restarted. Please also see Restarting Koji
Anytime postgresql is restarted Mirror Manager will need to be restarted, no SOP currently exists for this
Vacuuming Mirror Manager
Occasionally our vacuum cron jobs may not keep up with the writes to the mirrormanager database. If this happens, we need to do a vacuum full of mirrormanager's db. (See the dirty table section for a query to tell if this is necessary). The trick with this is making sure the mirrorlist cache isn't updated while we're doing the vacuum. To disable that we can turn off the mirrormanager management interface:
$ for i in 2 3 4 5; do ssh app$i supervisorctl stop mirrormanager ; done $ ssh db2 $ sudo -u postgres vacuumdb -fzv --dbname mirrormanager $ for i in 2 3 4 5; do ssh app$i supervisorctl start mirrormanager ; done
Anytime postgresql is restarted Bodhi will need to be restarted no sop currently exists for this.
Anytime MySQL is restarted, Smolt will need to be restarted. no SOP currently exists for this