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PostgreSQL Unleashed

Marian Marinov
Head of System Operations at Siteground.com

What is this talk about

Storage Architecture

Authentication

Commands

Writing Functions

Storage Architecture

File system structure

Default directory /var/lib/pgsql/data (PGDATA)/|- postgresql.conf|- pg_hba.conf|- pg_ident.conf|- postmaster.opts|- postmaster.pid|- PG_VERSION|- baseper-database subdirectories|- globalcluster-wide tables, such as pg_database|- pg_clogtransaction commit status data|- pg_multixactmultitransaction status data|- pg_stat_tmptemporary files for the statistics subsystem|- pg_subtranssubtransaction status data|- pg_tblspcsymbolic links to tablespaces|- pg_twophasestate files for prepared transactions|- pg_xlogWAL (Write Ahead Log) files

File system structure

Directory representation:

base -\|- 1|- 11510|- 11511|- 16384\- 24576

template1=# SELECT datname,datlastsysoid FROM pg_database; datname| datlastsysoid-----------------+--------------- template1|11510 template0|11510 postgres|11510 os|11510(5 rows)

File system structure

Directory representation:

base -\|- 11510 -\||- 24765

os# SELECT relname,relfilenode,reltablespace FROM pg_classWHERE relfilenode=24765;

Relname| relfilenode| reltablespace-------------+----------------+--------------- disk_io| 24765| 0(1 row)

File system structure

Table and Indexes are stored in separate files

Tables bigger then 1GB are split into different files:

filenode.1, filenode.2, ..., filenode.N

The 1GB limit can be changed during build using with-segsize configure option.

DataBase Design

DBNAMESCHMEOBJECTS(table/view/sequence/domain)database-\ |- public |- scheme1-\ | |- table1 | |- table2 | |- view1 | |- view2 | |- seq1 | \- seq2 \- scheme2

Authentication

Authentication

pg_hba.conf Host based authenticationpg_ident.conf Identification information

Authentication methods: trust anyone to any DB

reject do not allow any connections (useful for filtering)

ident -use the system user name or what identd provided

password use cleartext passwords

md5 md5 encrypted passwords

pam use the Password Authentication Mechanism system

Authentication

pg_hba.conf:

localdatabase user auth-method[auth-options]hostdatabase user CIDR-addressauth-method[auth-options]hostssldatabase user CIDR-addressauth-method[auth-options]hostnossldatabase user CIDR-addressauth-method[auth-options]hostdatabase user IP-address IP-maskauth-method [auth-options]hostssldatabase user IP-address IP-maskauth-method [auth-options]hostnossldatabase user IP-address IP-maskauth-method [auth-options]

Authentication

pg_ident.conf:

map-name system-username database-username

example:

# MAPNAMESYSTEM-USERNAMEPG-USERNAMEomicronbryanhbryanhomicronannann# bob has user name robert on these machinesomicronrobertbob# bryanh can also connect as guest1omicronbryanhguest1

Permissions

Every object has its own privileges:

Database privileges

Scheme privileges

Table privileges

View privileges

Sequence privileges

Function privileges

Domain privileges

Commands

Commands

Manage users:

CREATE ROLE xxx PASSWORD 'string'

ALTER ROLE username PASSWORD 'string'ALTER ROLE username SET enable_indexscan TO offALTER ROLE username RESET varname

GRANT CONNECT ON DATABASE 'xxx' TO 'username'GRANT UPDATE ON accounts TO usernameREVOKE ALL ON accounts FROM PUBLIC

DROP ROLE username

Commands

Manage databases:

List all databases:SELECT datname FROM pg_database;Or use \l from the CLI.

Create DB using the default template:CREATE DATABASE name;CREATE DATABASE name OWNER username;# createdb -O rolename dbname

Create DB using different templates:CREATE DATABASE dbname TEMPLATE template0;# createdb -T template0 dbname

Commands

Manage databases:

ALTER DATABASE mydb SET geqo TO off;

DROP DATABASE name;dropdb dbname

Manage tablespaces:

CREATE TABLESPACE space1 LOCATION '/mnt/sda1/pgsql/data';CREATE TABLE foo(i int) TABLESPACE space1;SET default_tablespace = space1;CREATE TABLE foo(i int);

SELECT spcname FROM pg_tablespace;

Commands

Database maintanance:

Vaccuming

To recover or reuse disk space occupied by updated or deleted rows.

To update data statistics used by the PostgreSQL query planner.

To protect against loss of very old data due to transaction ID wraparound.

Routine Reindexing

Log File Maintenance

$ pg_ctl start | rotatelogs /var/log/pgsql_log 86400

Backup

Backup

SQL dump

File system level backup

Continuous archiving

Writing Functions

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