历史版本。 PostgreSQL 9.1 已结束支持。 2016-10-27. 请参阅 当前版本手册.
45.3. pg_am #
目录pg_am存储关于索引访问方法的信息。系统支持的每种索引访问方法在这个目录中都有一行。此目录的内容在第 52 章中详细讨论。
表 45.3. pg_am 列
| Name | Type | References | Description |
|---|---|---|---|
amname | name | Name of the access method | |
amstrategies | int2 | Number of operator strategies for this access method, or zero if access method does not have a fixed set of operator strategies | |
amsupport | int2 | Number of support routines for this access method | |
amcanorder | bool | Does the access method support ordered scans sorted by the indexed column's value? | |
amcanorderbyop | bool | Does the access method support ordered scans sorted by the result of an operator on the indexed column? | |
amcanbackward | bool | Does the access method support backward scanning? | |
amcanunique | bool | Does the access method support unique indexes? | |
amcanmulticol | bool | Does the access method support multicolumn indexes? | |
amoptionalkey | bool | Does the access method support a scan without any constraint for the first index column? | |
amsearchnulls | bool | Does the access method support IS NULL/NOT NULL searches? | |
amstorage | bool | Can index storage data type differ from column data type? | |
amclusterable | bool | Can an index of this type be clustered on? | |
ampredlocks | bool | Does an index of this type manage fine-grained predicate locks? | |
amkeytype | oid | | Type of data stored in index, or zero if not a fixed type |
aminsert | regproc | | “Insert this tuple” function |
ambeginscan | regproc | | “Prepare for index scan” function |
amgettuple | regproc | | “Next valid tuple” function, or zero if none |
amgetbitmap | regproc | | “Fetch all valid tuples” function, or zero if none |
amrescan | regproc | | “(Re)start index scan” function |
amendscan | regproc | | “Clean up after index scan” function |
ammarkpos | regproc | | “Mark current scan position” function |
amrestrpos | regproc | | “Restore marked scan position” function |
ambuild | regproc | | “Build new index” function |
ambuildempty | regproc | | “Build empty index” function |
ambulkdelete | regproc | | Bulk-delete function |
amvacuumcleanup | regproc | | Post-VACUUM cleanup function |
amcostestimate | regproc | | Function to estimate cost of an index scan |
amoptions | regproc | | Function to parse and validate reloptions for an index |