mirror of
https://github.com/ClickHouse/ClickHouse.git
synced 2024-09-23 18:20:50 +00:00
115 lines
4.6 KiB
ReStructuredText
115 lines
4.6 KiB
ReStructuredText
system.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:
|
|
|
|
.. code-block:: sql
|
|
|
|
SELECT *
|
|
FROM system.replicas
|
|
WHERE table = 'visits'
|
|
FORMAT Vertical
|
|
|
|
Row 1:
|
|
──────
|
|
database: merge
|
|
table: visits
|
|
engine: ReplicatedCollapsingMergeTree
|
|
is_leader: 1
|
|
is_readonly: 0
|
|
is_session_expired: 0
|
|
future_parts: 1
|
|
parts_to_check: 0
|
|
zookeeper_path: /clickhouse/tables/01-06/visits
|
|
replica_name: example01-06-1.yandex.ru
|
|
replica_path: /clickhouse/tables/01-06/visits/replicas/example01-06-1.yandex.ru
|
|
columns_version: 9
|
|
queue_size: 1
|
|
inserts_in_queue: 0
|
|
merges_in_queue: 1
|
|
log_max_index: 596273
|
|
log_pointer: 596274
|
|
total_replicas: 2
|
|
active_replicas: 2
|
|
|
|
Столбцы:
|
|
::
|
|
database: Database name.
|
|
table: Table name.
|
|
engine: Table engine name.
|
|
|
|
is_leader: Whether the replica is the leader.
|
|
Only one replica can be the leader at a time. The leader is responsible for selecting background merges to perform.
|
|
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.
|
|
|
|
is_readonly: Whether the replica is in read-only mode.
|
|
This mode is turned on if the config doesn't have sections with ZK, if an unknown error occurred when reinitializing sessions in ZK, and during session reinitialization in ZK.
|
|
|
|
is_session_expired: Whether the session with ZK has expired.
|
|
Basically the same as 'is_readonly'.
|
|
|
|
future_parts: The number of data parts that will appear as the result of INSERTs or merges that haven't been done yet.
|
|
|
|
parts_to_check: 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: Path to table data in ZK.
|
|
replica_name: Replica name in ZK. Different replicas of the same table have different names.
|
|
replica_path: Path to replica data in ZK. The same as concatenating 'zookeeper_path/replicas/replica_path'.
|
|
|
|
columns_version: 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: 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: 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: The number of merges waiting to be made. Sometimes merges are lengthy, so this value may be greater than one for a long time.
|
|
|
|
The next 4 columns have a non-zero value only where there is an active session with ZK.
|
|
|
|
log_max_index: Maximum entry number in the log of general activity.
|
|
log_pointer: Maximum entry number from the log of general activity that the replica copied to its queue for execution, plus one.
|
|
If log_pointer is much smaller than log_max_index, something is wrong.
|
|
|
|
total_replicas: The total number of known replicas of this table.
|
|
active_replicas: The number of replicas of this table that have a session in ZK (i.e., the number of functioning replicas).к
|
|
|
|
If you request all the columns, the table may work a bit slowly, since several reads from ZK are made for each row.
|
|
If you don't 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:
|
|
|
|
.. code-block:: 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 doesn't return anything, it means that everything is fine.
|