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The catalog pg_am stores information about index access methods. There is one row for each index access method supported by the system. The contents of this catalog are discussed in detail in Chapter 49.
Table 43-3. pg_am Columns
| Name | Type | References | Description |
|---|---|---|---|
| amname | name | Name of the access method | |
| amstrategies | int2 | Number of operator strategies for this access method | |
| amsupport | int2 | Number of support routines for this access method | |
| amorderstrategy | int2 | Zero if the index offers no sort order, otherwise the strategy number of the strategy operator that describes the sort order | |
| 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? | |
| amindexnulls | bool | Does the access method support null index entries? | |
| amstorage | bool | Can index storage data type differ from column data type? | |
| amclusterable | bool | Can an index of this type be clustered on? | |
| aminsert | regproc | pg_proc.oid | "Insert this tuple" function |
| ambeginscan | regproc | pg_proc.oid | "Start new scan" function |
| amgettuple | regproc | pg_proc.oid | "Next valid tuple" function |
| amgetmulti | regproc | pg_proc.oid | "Fetch multiple tuples" function |
| amrescan | regproc | pg_proc.oid | "Restart this scan" function |
| amendscan | regproc | pg_proc.oid | "End this scan" function |
| ammarkpos | regproc | pg_proc.oid | "Mark current scan position" function |
| amrestrpos | regproc | pg_proc.oid | "Restore marked scan position" function |
| ambuild | regproc | pg_proc.oid | "Build new index" function |
| ambulkdelete | regproc | pg_proc.oid | Bulk-delete function |
| amvacuumcleanup | regproc | pg_proc.oid | Post-VACUUM cleanup function |
| amcostestimate | regproc | pg_proc.oid | Function to estimate cost of an index scan |
| amoptions | regproc | pg_proc.oid | Function to parse and validate reloptions for an index |