PG_AM

Updated on 2024-09-30 GMT+08:00

View PDF

PG_AM records information about index access methods. There is one row for each index access method supported by the system.

**Table 1** PG_AM columns
Name	Type	Reference	Description
oid	oid	-	Row identifier (hidden attribute; must be explicitly selected)
amname	name	-	Name of the access method
amstrategies	smallint	-	Number of operator strategies for this access method, or zero if access method does not have a fixed set of operator strategies
amsupport	smallint	-	Number of support routines for this access method
amcanorder	boolean	-	Whether the access method supports ordered scans sorted by the indexed column's value
amcanorderbyop	boolean	-	Whether the access method supports ordered scans sorted by the result of an operator on the indexed column
amcanbackward	boolean	-	Whether the access method supports backward scanning
amcanunique	boolean	-	Whether the access method supports unique indexes
amcanmulticol	boolean	-	Whether the access method supports multi-column indexes
amoptionalkey	boolean	-	Whether the access method supports a scan without any constraint for the first index column
amsearcharray	boolean	-	Whether the access method supports ScalarArrayOpExpr searches
amsearchnulls	boolean	-	Whether the access method supports IS NULL/NOT NULL searches
amstorage	boolean	-	Whether an index storage data type can differ from a column data type
amclusterable	boolean	-	Whether an index of this type can be clustered on
ampredlocks	boolean	-	Whether an index of this type manages fine-grained predicate locks
amkeytype	oid	PG_TYPE.oid	Type of data stored in index, or zero if not a fixed type
aminsert	regproc	PG_PROC.oid	"Insert this tuple" function
ambeginscan	regproc	PG_PROC.oid	"Prepare for index scan" function
amgettuple	regproc	PG_PROC.oid	"Next valid tuple" function, or zero if none
amgetbitmap	regproc	PG_PROC.oid	"Fetch all valid tuples" function, or zero if none
amrescan	regproc	PG_PROC.oid	"(Re)start index scan" function
amendscan	regproc	PG_PROC.oid	"Clean up after index scan" function
ammarkpos	regproc	PG_PROC.oid	"Mark current scan position" function
amrestrpos	regproc	PG_PROC.oid	"Restore marked scan position" function
ammerge	regproc	PG_PROC.oid	"Merge multiple indexes" function
ambuild	regproc	PG_PROC.oid	"Build new index" function
ambuildempty	regproc	PG_PROC.oid	"Build empty index" function
ambulkdelete	regproc	PG_PROC.oid	Bulk-delete function
amvacuumcleanup	regproc	PG_PROC.oid	Post-VACUUM cleanup function
amcanreturn	regproc	PG_PROC.oid	Function to check whether index supports index-only scans, or zero if none
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