mirror of
https://github.com/ClickHouse/ClickHouse.git
synced 2024-11-27 18:12:02 +00:00
133 lines
6.7 KiB
Markdown
133 lines
6.7 KiB
Markdown
# system.replicas {#system_tables-replicas}
|
||
|
||
Contains information and status for replicated tables residing on the local server.
|
||
This table can be used for monitoring. The table contains a row for every Replicated\* table.
|
||
|
||
Example:
|
||
|
||
``` sql
|
||
SELECT *
|
||
FROM system.replicas
|
||
WHERE table = 'test_table'
|
||
FORMAT Vertical
|
||
```
|
||
|
||
``` text
|
||
Query id: dc6dcbcb-dc28-4df9-ae27-4354f5b3b13e
|
||
|
||
Row 1:
|
||
───────
|
||
database: db
|
||
table: test_table
|
||
engine: ReplicatedMergeTree
|
||
is_leader: 1
|
||
can_become_leader: 1
|
||
is_readonly: 0
|
||
is_session_expired: 0
|
||
future_parts: 0
|
||
parts_to_check: 0
|
||
zookeeper_path: /test/test_table
|
||
replica_name: r1
|
||
replica_path: /test/test_table/replicas/r1
|
||
columns_version: -1
|
||
queue_size: 27
|
||
inserts_in_queue: 27
|
||
merges_in_queue: 0
|
||
part_mutations_in_queue: 0
|
||
queue_oldest_time: 2021-10-12 14:48:48
|
||
inserts_oldest_time: 2021-10-12 14:48:48
|
||
merges_oldest_time: 1970-01-01 03:00:00
|
||
part_mutations_oldest_time: 1970-01-01 03:00:00
|
||
oldest_part_to_get: 1_17_17_0
|
||
oldest_part_to_merge_to:
|
||
oldest_part_to_mutate_to:
|
||
log_max_index: 206
|
||
log_pointer: 207
|
||
last_queue_update: 2021-10-12 14:50:08
|
||
absolute_delay: 99
|
||
total_replicas: 5
|
||
active_replicas: 5
|
||
last_queue_update_exception:
|
||
zookeeper_exception:
|
||
replica_is_active: {'r1':1,'r2':1}
|
||
```
|
||
|
||
Columns:
|
||
|
||
- `database` (`String`) - Database name
|
||
- `table` (`String`) - Table name
|
||
- `engine` (`String`) - Table engine name
|
||
- `is_leader` (`UInt8`) - Whether the replica is the leader.
|
||
Multiple replicas can be leaders at the same time. A replica can be prevented from becoming a leader using the `merge_tree` setting `replicated_can_become_leader`. The leaders are responsible for scheduling background merges.
|
||
Note that writes can be performed to any replica that is available and has a session in ZK, regardless of whether it is a leader.
|
||
- `can_become_leader` (`UInt8`) - Whether the replica can be a leader.
|
||
- `is_readonly` (`UInt8`) - Whether the replica is in read-only mode.
|
||
This mode is turned on if the config does not have sections with ZooKeeper, if an unknown error occurred when reinitializing sessions in ZooKeeper, and during session reinitialization in ZooKeeper.
|
||
- `is_session_expired` (`UInt8`) - the session with ZooKeeper has expired. Basically the same as `is_readonly`.
|
||
- `future_parts` (`UInt32`) - The number of data parts that will appear as the result of INSERTs or merges that haven’t been done yet.
|
||
- `parts_to_check` (`UInt32`) - The number of data parts in the queue for verification. A part is put in the verification queue if there is suspicion that it might be damaged.
|
||
- `zookeeper_path` (`String`) - Path to table data in ZooKeeper.
|
||
- `replica_name` (`String`) - Replica name in ZooKeeper. Different replicas of the same table have different names.
|
||
- `replica_path` (`String`) - Path to replica data in ZooKeeper. The same as concatenating ‘zookeeper_path/replicas/replica_path’.
|
||
- `columns_version` (`Int32`) - Version number of the table structure. Indicates how many times ALTER was performed. If replicas have different versions, it means some replicas haven’t made all of the ALTERs yet.
|
||
- `queue_size` (`UInt32`) - Size of the queue for operations waiting to be performed. Operations include inserting blocks of data, merges, and certain other actions. It usually coincides with `future_parts`.
|
||
- `inserts_in_queue` (`UInt32`) - Number of inserts of blocks of data that need to be made. Insertions are usually replicated fairly quickly. If this number is large, it means something is wrong.
|
||
- `merges_in_queue` (`UInt32`) - The number of merges waiting to be made. Sometimes merges are lengthy, so this value may be greater than zero for a long time.
|
||
- `part_mutations_in_queue` (`UInt32`) - The number of mutations waiting to be made.
|
||
- `queue_oldest_time` (`DateTime`) - If `queue_size` greater than 0, shows when the oldest operation was added to the queue.
|
||
- `inserts_oldest_time` (`DateTime`) - See `queue_oldest_time`
|
||
- `merges_oldest_time` (`DateTime`) - See `queue_oldest_time`
|
||
- `part_mutations_oldest_time` (`DateTime`) - See `queue_oldest_time`
|
||
|
||
The next 4 columns have a non-zero value only where there is an active session with ZK.
|
||
|
||
- `log_max_index` (`UInt64`) - Maximum entry number in the log of general activity.
|
||
- `log_pointer` (`UInt64`) - Maximum entry number in the log of general activity that the replica copied to its execution queue, plus one. If `log_pointer` is much smaller than `log_max_index`, something is wrong.
|
||
- `last_queue_update` (`DateTime`) - When the queue was updated last time.
|
||
- `absolute_delay` (`UInt64`) - How big lag in seconds the current replica has.
|
||
- `total_replicas` (`UInt8`) - The total number of known replicas of this table.
|
||
- `active_replicas` (`UInt8`) - The number of replicas of this table that have a session in ZooKeeper (i.e., the number of functioning replicas).
|
||
- `last_queue_update_exception` (`String`) - When the queue contains broken entries. Especially important when ClickHouse breaks backward compatibility between versions and log entries written by newer versions aren't parseable by old versions.
|
||
- `zookeeper_exception` (`String`) - The last exception message, got if the error happened when fetching the info from ZooKeeper.
|
||
- `replica_is_active` ([Map(String, UInt8)](../../sql-reference/data-types/map.md)) — Map between replica name and is replica active.
|
||
|
||
If you request all the columns, the table may work a bit slowly, since several reads from ZooKeeper are made for each row.
|
||
If you do not request the last 4 columns (log_max_index, log_pointer, total_replicas, active_replicas), the table works quickly.
|
||
|
||
For example, you can check that everything is working correctly like this:
|
||
|
||
``` sql
|
||
SELECT
|
||
database,
|
||
table,
|
||
is_leader,
|
||
is_readonly,
|
||
is_session_expired,
|
||
future_parts,
|
||
parts_to_check,
|
||
columns_version,
|
||
queue_size,
|
||
inserts_in_queue,
|
||
merges_in_queue,
|
||
log_max_index,
|
||
log_pointer,
|
||
total_replicas,
|
||
active_replicas
|
||
FROM system.replicas
|
||
WHERE
|
||
is_readonly
|
||
OR is_session_expired
|
||
OR future_parts > 20
|
||
OR parts_to_check > 10
|
||
OR queue_size > 20
|
||
OR inserts_in_queue > 10
|
||
OR log_max_index - log_pointer > 10
|
||
OR total_replicas < 2
|
||
OR active_replicas < total_replicas
|
||
```
|
||
|
||
If this query does not return anything, it means that everything is fine.
|
||
|
||
[Original article](https://clickhouse.com/docs/en/operations/system-tables/replicas) <!--hide-->
|
||
|