pg_undo

The catalog pg_undo contains part of the information about undo segments. The rest is mostly in pg_class.

Table. pg_undo Columns

Name	Type	Description
`undoid`	`oid`	The ID of this undo segment, the system assigns sequentially from 1
`undrelid`	`oid`	The OID of the `pg_class` entry for this undo segment
`undusecount`	`int8`	The number of times the transaction table entry in this undo segment has been reused, this field will only be updated when the undo segment is deleted
`undreusetime`	`logicaltime`	The logical timestamp of when the transaction table entry in this undo segment was reused, this field will only be updated when the undo segment is deleted
`undisvalid`	`bool`	If true, the undo segment can currently be used to provide read consistency. False means the undo segment has been completely deleted
`undislive`	`bool`	If false, the undo segment has been deleted