{"Entry":{"collection":"storage","key":"fork-main","name":"main fork","aliases":[],"metadata":{"aliases":[],"category":"Relation forks","content_hash":"bfe645087c5dba79074341ba6a7521bccf73af4507e45a60b42d7f1793e09b27","imported_at":"2026-09-30T00:40:47.132084+08:00","name":"main fork","name_zh":"","slug":"fork-main","summary":"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 process number 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 66.3 ), 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 66.4 . 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 66.5 )."}},"Definition":{"Collection":"storage","Key":"fork-main","SourceDatabase":"center","Version":"18","SourceTable":"storage_structure","SourceKey":"fork-main","SourceRevision":"555610c24d53e4316da5b7d3fc25c279d96856d5e0e23ee308c328c5fa881d9f","Facts":{"comparison_data":{"fork":"main"},"comparison_hash":"9d354a5e3ce1acfea4ce84c5aa725c3ea2533ffd4a9717a0a64fba8f72e4706c","description":["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 process number 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 66.3 ), 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 66.4 . 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 66.5 ).","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."],"facts":[{"label":"Fork","value":"main"}],"manual_html":"","manual_path":"/docs/18/storage-file-layout.html","related":[{"label":"Database file layout","url":"/wiki/storage/storage-file-layout/?v=18"}],"release":{"channel":"stable","label":"18.6","major":"18","ref":"https://ftp.postgresql.org/pub/source/v18.6/postgresql-18.6.tar.bz2","revision":"555610c24d53e4316da5b7d3fc25c279d96856d5e0e23ee308c328c5fa881d9f"},"sections":[],"signature":"","sources":[{"label":"PostgreSQL 18 English manual","path":"storage-file-layout.html","sha256":"8cdf46b5af669f41f0a77c2541863d63454ef8fbb44d22a75e576cf1a7efc9c9","url":"/docs/18/storage-file-layout.html"}],"tables":[]},"ManualEvidence":{"manual_path":"/docs/18/storage-file-layout.html","release":{"channel":"stable","label":"18.6","major":"18","ref":"https://ftp.postgresql.org/pub/source/v18.6/postgresql-18.6.tar.bz2","revision":"555610c24d53e4316da5b7d3fc25c279d96856d5e0e23ee308c328c5fa881d9f"},"sources":[{"label":"PostgreSQL 18 English manual","path":"storage-file-layout.html","sha256":"8cdf46b5af669f41f0a77c2541863d63454ef8fbb44d22a75e576cf1a7efc9c9","url":"/docs/18/storage-file-layout.html"}]},"MeasuredEvidence":{}},"Text":{"Collection":"storage","Key":"fork-main","SourceDatabase":"center","Version":"18","Locale":"en","Title":"main fork","Summary":"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 process number 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 66.3 ), 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 66.4 . 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 66.5 ).\nThe 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.","BodyHTML":"\u003cp\u003eEach table and index is stored in a separate file. For ordinary relations, these files are named after the table or index\u0026#39;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 process number 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 66.3 ), 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 66.4 . 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 66.5 ).\nThe 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.\u003c/p\u003e","SourceRevision":"555610c24d53e4316da5b7d3fc25c279d96856d5e0e23ee308c328c5fa881d9f","ContentHash":"ad329e874516836cfcf16d367bc027319cc79c785a3025a2ac543d537d4242dc","Payload":{"description":["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 process number 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 66.3 ), 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 66.4 . 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 66.5 ).","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."],"manual_html":"","related":[{"label":"Database file layout","url":"/wiki/storage/storage-file-layout/?v=18"}],"sections":[],"tables":[]}},"RequestedLocale":"zh-Hans","Fallback":true,"Versions":["10","11","12","13","14","15","16","17","18","19","20"],"Locales":["en"],"Signatures":null,"Spellings":null,"SQLState":null,"Evidence":null}