system.replication_queue

Contains information about tasks from replication queues stored in ZooKeeper for tables in the ReplicatedMergeTree family.

Columns:

database (String) — Name of the database.
table (String) — Name of the table.
replica_name (String) — Replica name in ZooKeeper. Different replicas of the same table have different names.
position (UInt32) — Position of the task in the queue.
node_name (String) — Node name in ZooKeeper.
type (String) — Type of the task in the queue, one of:
- GET_PART — Get the part from another replica.
- ATTACH_PART — Attach the part, possibly from our own replica (if found in the detached folder). You may think of it as a GET_PART with some optimizations as they're nearly identical.
- MERGE_PARTS — Merge the parts.
- DROP_RANGE — Delete the parts in the specified partition in the specified number range.
- CLEAR_COLUMN — NOTE: Deprecated. Drop specific column from specified partition.
- CLEAR_INDEX — NOTE: Deprecated. Drop specific index from specified partition.
- REPLACE_RANGE — Drop a certain range of parts and replace them with new ones.
- MUTATE_PART — Apply one or several mutations to the part.
- ALTER_METADATA — Apply alter modification according to global /metadata and /columns paths.
create_time (Datetime) — Date and time when the task was submitted for execution.
required_quorum (UInt32) — The number of replicas waiting for the task to complete with confirmation of completion. This column is only relevant for the GET_PARTS task.
source_replica (String) — Name of the source replica.
new_part_name (String) — Name of the new part.
parts_to_merge (Array (String)) — Names of parts to merge or update.
is_detach (UInt8) — The flag indicates whether the DETACH_PARTS task is in the queue.
is_currently_executing (UInt8) — The flag indicates whether a specific task is being performed right now.
num_tries (UInt32) — The number of failed attempts to complete the task.
last_exception (String) — Text message about the last error that occurred (if any).
last_attempt_time (Datetime) — Date and time when the task was last attempted.
num_postponed (UInt32) — The number of postponed tasks.
postpone_reason (String) — The reason why the task was postponed.
last_postpone_time (Datetime) — Date and time when the task was last postponed.
merge_type (String) — Type of the current merge. Empty if it's a mutation.

Example

SELECT * FROM system.replication_queue LIMIT 1 FORMAT Vertical;

Row 1:
──────
database:               merge
table:                  visits_v2
replica_name:           mtgiga001-1t.metrika.yandex.net
position:               15
node_name:              queue-0009325559
type:                   MERGE_PARTS
create_time:            2020-12-07 14:04:21
required_quorum:        0
source_replica:         mtgiga001-1t.metrika.yandex.net
new_part_name:          20201130_121373_121384_2
parts_to_merge:         ['20201130_121373_121378_1','20201130_121379_121379_0','20201130_121380_121380_0','20201130_121381_121381_0','20201130_121382_121382_0','20201130_121383_121383_0','20201130_121384_121384_0']
is_detach:              0
is_currently_executing: 0
num_tries:              36
last_exception:         Code: 226, e.displayText() = DB::Exception: Marks file '/opt/clickhouse/data/merge/visits_v2/tmp_fetch_20201130_121373_121384_2/CounterID.mrk' does not exist (version 20.8.7.15 (official build))
last_attempt_time:      2020-12-08 17:35:54
num_postponed:          0
postpone_reason:
last_postpone_time:     1970-01-01 03:00:00

See Also

Managing ReplicatedMergeTree Tables

Original article