Where are PostgreSQL databases stored on my computer?
So this might be a stupid question, but I’m really new to this. So I’m making a Postgres database on the postgres server, that I started up with this command:
Which supposedly created the database. But where is this database? Where can I find it on my computer?
I recommend starting with postgresql.org/docs/current/static/tutorial.html . And you didn’t start PostgreSQL with the psql command, you connected to it; it’s a server and psql is the client.
The «database» is not a single file that you can take with you or look at. A database server manages this differently than e.g. Microsoft Access.
5 Answers 5
Where exactly your data is stored depends on how you installed and configured PostgreSQL. Running the
command as the postgres user (from inside the psql tool or another client) will tell you where it is though. For example, if you installed it from the debian or ubuntu repositories you would probably find your data files are somewhere like /var/lib/postgresql/9.2/main.
There probably isn’t anything terribly interesting in there though. Sometimes there are a few configuration files like pg_hba.conf (the windows version puts them there at least) but if you’re on debian you’ll find those under /etc/postgresql/.
If you’re expecting your database to be a single file that you can move around between systems, etc, you’re probably better off using a simpler embedded database like sqlite.
Где postgresql хранит базы linux
This section describes the storage format at the level of files and directories.
Traditionally, the configuration and data files used by a database cluster are stored together within the cluster’s data directory, commonly referred to as PGDATA (after the name of the environment variable that can be used to define it). A common location for PGDATA is /var/lib/pgsql/data . Multiple clusters, managed by different server instances, can exist on the same machine.
The PGDATA directory contains several subdirectories and control files, as shown in Table 73.1. In addition to these required items, the cluster configuration files postgresql.conf , pg_hba.conf , and pg_ident.conf are traditionally stored in PGDATA , although it is possible to place them elsewhere.
Table 73.1. Contents of PGDATA
| Item | Description |
|---|---|
| PG_VERSION | A file containing the major version number of PostgreSQL |
| base | Subdirectory containing per-database subdirectories |
| current_logfiles | File recording the log file(s) currently written to by the logging collector |
| global | Subdirectory containing cluster-wide tables, such as pg_database |
| pg_commit_ts | Subdirectory containing transaction commit timestamp data |
| pg_dynshmem | Subdirectory containing files used by the dynamic shared memory subsystem |
| pg_logical | Subdirectory containing status data for logical decoding |
| pg_multixact | Subdirectory containing multitransaction status data (used for shared row locks) |
| pg_notify | Subdirectory containing LISTEN/NOTIFY status data |
| pg_replslot | Subdirectory containing replication slot data |
| pg_serial | Subdirectory containing information about committed serializable transactions |
| pg_snapshots | Subdirectory containing exported snapshots |
| pg_stat | Subdirectory containing permanent files for the statistics subsystem |
| pg_stat_tmp | Subdirectory containing temporary files for the statistics subsystem |
| pg_subtrans | Subdirectory containing subtransaction status data |
| pg_tblspc | Subdirectory containing symbolic links to tablespaces |
| pg_twophase | Subdirectory containing state files for prepared transactions |
| pg_wal | Subdirectory containing WAL (Write Ahead Log) files |
| pg_xact | Subdirectory containing transaction commit status data |
| postgresql.auto.conf | A file used for storing configuration parameters that are set by ALTER SYSTEM |
| postmaster.opts | A file recording the command-line options the server was last started with |
| postmaster.pid | A lock file recording the current postmaster process ID (PID), cluster data directory path, postmaster start timestamp, port number, Unix-domain socket directory path (could be empty), first valid listen_address (IP address or * , or empty if not listening on TCP), and shared memory segment ID (this file is not present after server shutdown) |
For each database in the cluster there is a subdirectory within PGDATA /base , named after the database’s OID in pg_database . This subdirectory is the default location for the database’s files; in particular, its system catalogs are stored there.
Note that the following sections describe the behavior of the builtin heap table access method, and the builtin index access methods. Due to the extensible nature of PostgreSQL , other access methods might work differently.
Each table and index is stored in a separate file. For ordinary relations, these files are named after the table or index’s filenode number, which can be found in pg_class . relfilenode . But for temporary relations, the file name is of the form t BBB _ FFF , where BBB is the backend ID of the backend which created the file, and FFF is the filenode number. In either case, in addition to the main file (a/k/a main fork), each table and index has a free space map (see Section 73.3), which stores information about free space available in the relation. The free space map is stored in a file named with the filenode number plus the suffix _fsm . Tables also have a visibility map, stored in a fork with the suffix _vm , to track which pages are known to have no dead tuples. The visibility map is described further in Section 73.4. Unlogged tables and indexes have a third fork, known as the initialization fork, which is stored in a fork with the suffix _init (see Section 73.5).
Caution
Note that while a table’s filenode often matches its OID, this is not necessarily the case; some operations, like TRUNCATE , REINDEX , CLUSTER and some forms of ALTER TABLE , can change the filenode while preserving the OID. Avoid assuming that filenode and table OID are the same. Also, for certain system catalogs including pg_class itself, pg_class . relfilenode contains zero. The actual filenode number of these catalogs is stored in a lower-level data structure, and can be obtained using the pg_relation_filenode() function.
When a table or index exceeds 1 GB, it is divided into gigabyte-sized segments. The first segment’s file name is the same as the filenode; subsequent segments are named filenode.1, filenode.2, etc. This arrangement avoids problems on platforms that have file size limitations. (Actually, 1 GB is just the default segment size. The segment size can be adjusted using the configuration option —with-segsize when building PostgreSQL .) In principle, free space map and visibility map forks could require multiple segments as well, though this is unlikely to happen in practice.
A table that has columns with potentially large entries will have an associated TOAST table, which is used for out-of-line storage of field values that are too large to keep in the table rows proper. pg_class . reltoastrelid links from a table to its TOAST table, if any. See Section 73.2 for more information.
The contents of tables and indexes are discussed further in Section 73.6.
Tablespaces make the scenario more complicated. Each user-defined tablespace has a symbolic link inside the PGDATA /pg_tblspc directory, which points to the physical tablespace directory (i.e., the location specified in the tablespace’s CREATE TABLESPACE command). This symbolic link is named after the tablespace’s OID. Inside the physical tablespace directory there is a subdirectory with a name that depends on the PostgreSQL server version, such as PG_9.0_201008051 . (The reason for using this subdirectory is so that successive versions of the database can use the same CREATE TABLESPACE location value without conflicts.) Within the version-specific subdirectory, there is a subdirectory for each database that has elements in the tablespace, named after the database’s OID. Tables and indexes are stored within that directory, using the filenode naming scheme. The pg_default tablespace is not accessed through pg_tblspc , but corresponds to PGDATA /base . Similarly, the pg_global tablespace is not accessed through pg_tblspc , but corresponds to PGDATA /global .
The pg_relation_filepath() function shows the entire path (relative to PGDATA ) of any relation. It is often useful as a substitute for remembering many of the above rules. But keep in mind that this function just gives the name of the first segment of the main fork of the relation — you may need to append a segment number and/or _fsm , _vm , or _init to find all the files associated with the relation.
Temporary files (for operations such as sorting more data than can fit in memory) are created within PGDATA /base/pgsql_tmp , or within a pgsql_tmp subdirectory of a tablespace directory if a tablespace other than pg_default is specified for them. The name of a temporary file has the form pgsql_tmp PPP . NNN , where PPP is the PID of the owning backend and NNN distinguishes different temporary files of that backend.
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Структура каталогов и файлов PostgreSQL¶
СУБД PostgreSQL в разных операционных системах имеет практически идентичную структуру каталогов. В данной статье рассматривается стандартная структура каталогов для ОС Ubuntu 12.04.
По умолчанию PostgreSQL устанавливается в папку /var/lib/postgresql//main. Основной каталог СУБД содержит подкаталоги с пользовательскими данными и служебной информацией.
- postmaster.opts — файл, в котором сдержится командная строка с параметрами, с помощью которой была запущена СУБД. На моем компьютере в этом файле хранится следующая строка
/usr/lib/postgresql/9.3/bin/postgres "-D" "/var/lib/postgresql/9.3/main" "-c" "config_file=/etc/postgresql/9.3/main/postgresql.conf"
root@server: /var/lib/postgresql/9.3/main/base# ls 1/ 12065/ 12070/ 16384/ 24580/
denis=# select oid, datname from pg_database; oid | datname -------+----------- 1 | template1 12065 | template0 12070 | postgres 16384 | denis 24580 | t1 (5 rows)
- транзакция стартовала,
- транзакция успешно завершена,
- транзакция отменена,
- подтранзакция успешно завершена.
Количество хранимых транзакций ограничено параметром autovacuum_freeze_max_age (максимальное значение ~ 2 миллиарда), который в свою очередь регулирует работу автовакума. Поэтому максимальный размер файла может быть ~ 0.5 Гб максимум.
Файлы создаются при вызове процедуры pg_export_snapshot() и существуют до окончания транзакции. Ниже представлена последовательность действий, позволяющая понять, как появляются и исчезают файлы в этом каталоге. Экспорт снапшота в транзакции
BEGIN denis=# SELECT pg_export_snapshot(); pg_export_snapshot -------------------- 00000312-1 (1 row)
root@server: /var/lib/postgresql/9.3/main/pg_snapshots# ls 00000312-1 root@server: /var/lib/postgresql/9.3/main/pg_snapshots# cat 00000312-1 xid:786 dbid:16384 iso:1 ro:0 xmin:786 xmax:786 xcnt:0 sof:0 sxcnt:0 rec:0
root@server: /var/lib/postgresql/9.3/main/pg_snapshots# l ----
Ниже показана последовательность действий, демонстрирующая, как в этом каталоге появляются файлы. Создается табличное пространство
denis=# CREATE TABLESPACE tmp LOCATION '/home/denis/1'; CREATE TABLESPACE
denis=# select oid, spcname from pg_tablespace; oid | spcname -------+------------ 1663 | pg_default 1664 | pg_global 27936 | tmp (3 rows)
Для каждого пользовательского табличного пространства в каталоге создается символьная ссылка на заданный каталог, именем этой ссылки является OID этого табличного пространства.
/var/lib/postgresql/9.3/main/pg_tblspc# ll total 8 drwx------ 2 postgres postgres 4096 Nov 4 09:51 ./ drwx------ 15 postgres postgres 4096 Nov 4 07:05 ../ lrwxrwxrwx 1 postgres postgres 13 Nov 4 09:51 27936 -> /home/denis/1/