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54.19. `pg_replication_slots`
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54.19. `pg_replication_slots` #

The pg_replication_slots view provides a listing of all replication slots that currently exist on the database cluster, along with their current state.

For more on replication slots, see Section 27.2.6 and Chapter 49.

Table 54.19. pg_replication_slots Columns

Column Type Description

Column Type Description
`slot_name` `name` A unique, cluster-wide identifier for the replication slot
`plugin` `name` The base name of the shared object containing the output plugin this logical slot is using, or null for physical slots.
`slot_type` `text` The slot type: `physical` or `logical`
`datoid` `oid` (references `pg_database`.`oid`) The OID of the database this slot is associated with, or null. Only logical slots have an associated database.
`database` `name` (references `pg_database`.`datname`) The name of the database this slot is associated with, or null. Only logical slots have an associated database.
`temporary` `bool` True if this is a temporary replication slot. Temporary slots are not saved to disk and are automatically dropped on error or when the session has finished.
`active` `bool` True if this slot is currently actively being used
`active_pid` `int4` The process ID of the session using this slot if the slot is currently actively being used. `NULL` if inactive.
`xmin` `xid` The oldest transaction that this slot needs the database to retain. `VACUUM` cannot remove tuples deleted by any later transaction.
`catalog_xmin` `xid` The oldest transaction affecting the system catalogs that this slot needs the database to retain. `VACUUM` cannot remove catalog tuples deleted by any later transaction.
`restart_lsn` `pg_lsn` The address (`LSN`) of oldest WAL which still might be required by the consumer of this slot and thus won’t be automatically removed during checkpoints unless this LSN gets behind more than max_slot_wal_keep_size from the current LSN. `NULL` if the `LSN` of this slot has never been reserved.
`confirmed_flush_lsn` `pg_lsn` The address (`LSN`) up to which the logical slot’s consumer has confirmed receiving data. Data corresponding to the transactions committed before this `LSN` is not available anymore. `NULL` for physical slots.
`wal_status` `text` Availability of WAL files claimed by this slot. Possible values are: `reserved` means that the claimed files are within `max_wal_size`. `extended` means that `max_wal_size` is exceeded but the files are still retained, either by the replication slot or by `wal_keep_size`. `unreserved` means that the slot no longer retains the required WAL files and some of them are to be removed at the next checkpoint. This state can return to `reserved` or `extended`. `lost` means that some required WAL files have been removed and this slot is no longer usable. The last two states are seen only when max_slot_wal_keep_size is non-negative. If `restart_lsn` is NULL, this field is null.
`safe_wal_size` `int8` The number of bytes that can be written to WAL such that this slot is not in danger of getting in state "lost". It is NULL for lost slots, as well as if `max_slot_wal_keep_size` is `-1`.
`two_phase` `bool` True if the slot is enabled for decoding prepared transactions. Always false for physical slots.
`conflicting` `bool` True if this logical slot conflicted with recovery (and so is now invalidated). Always NULL for physical slots.

slot_name name

A unique, cluster-wide identifier for the replication slot

plugin name

The base name of the shared object containing the output plugin this logical slot is using, or null for physical slots.

slot_type text

The slot type: physical or logical

datoid oid (references pg_database.oid)

The OID of the database this slot is associated with, or null. Only logical slots have an associated database.

database name (references pg_database.datname)

The name of the database this slot is associated with, or null. Only logical slots have an associated database.

temporary bool

True if this is a temporary replication slot. Temporary slots are not saved to disk and are automatically dropped on error or when the session has finished.

active bool

True if this slot is currently actively being used

active_pid int4

The process ID of the session using this slot if the slot is currently actively being used. NULL if inactive.

xmin xid

The oldest transaction that this slot needs the database to retain. VACUUM cannot remove tuples deleted by any later transaction.

catalog_xmin xid

The oldest transaction affecting the system catalogs that this slot needs the database to retain. VACUUM cannot remove catalog tuples deleted by any later transaction.

restart_lsn pg_lsn

The address (LSN) of oldest WAL which still might be required by the consumer of this slot and thus won’t be automatically removed during checkpoints unless this LSN gets behind more than max_slot_wal_keep_size from the current LSN. NULL if the LSN of this slot has never been reserved.

confirmed_flush_lsn pg_lsn

The address (LSN) up to which the logical slot’s consumer has confirmed receiving data. Data corresponding to the transactions committed before this LSN is not available anymore. NULL for physical slots.

wal_status text

Availability of WAL files claimed by this slot. Possible values are:

reserved means that the claimed files are within max_wal_size.
extended means that max_wal_size is exceeded but the files are still retained, either by the replication slot or by wal_keep_size.
unreserved means that the slot no longer retains the required WAL files and some of them are to be removed at the next checkpoint. This state can return to reserved or extended.
lost means that some required WAL files have been removed and this slot is no longer usable.

The last two states are seen only when max_slot_wal_keep_size is non-negative. If restart_lsn is NULL, this field is null.

safe_wal_size int8

The number of bytes that can be written to WAL such that this slot is not in danger of getting in state "lost". It is NULL for lost slots, as well as if max_slot_wal_keep_size is -1.

two_phase bool

True if the slot is enabled for decoding prepared transactions. Always false for physical slots.

conflicting bool

True if this logical slot conflicted with recovery (and so is now invalidated). Always NULL for physical slots.

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