Modify Configuration Dynamically

This document describes how to dynamically modify the cluster configuration.

You can dynamically update the configuration of components (including TiDB, TiKV, and PD) using SQL statements, without restarting the cluster components. Currently, the method of changing TiDB instance configuration is different from that of changing configuration of other components (such TiKV and PD).

Common Operations

This section describes the common operations of dynamically modifying configuration.

View instance configuration

To view the configuration of all instances in the cluster, use the show config statement. The result is as follows:

show config;

+------+-----------------+-----------------------------------------------------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Type | Instance        | Name                                                      | Value                                                                                                                                                                                                                                                                            |
+------+-----------------+-----------------------------------------------------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| tidb | 127.0.0.1:4001  | advertise-address                                         | 127.0.0.1                                                                                                                                                                                                                                                                        |
| tidb | 127.0.0.1:4001  | binlog.binlog-socket                                      |                                                                                                                                                                                                                                                                                  |
| tidb | 127.0.0.1:4001  | binlog.enable                                             | false                                                                                                                                                                                                                                                                            |
| tidb | 127.0.0.1:4001  | binlog.ignore-error                                       | false                                                                                                                                                                                                                                                                            |
| tidb | 127.0.0.1:4001  | binlog.strategy                                           | range                                                                                                                                                                                                                                                                            |
| tidb | 127.0.0.1:4001  | binlog.write-timeout                                      | 15s                                                                                                                                                                                                                                                                              |
| tidb | 127.0.0.1:4001  | check-mb4-value-in-utf8                                   | true                                                                                                                                                                                                                                                                             |

...

You can filter the result by fields. For example:

show config where type='tidb'
show config where instance in (...)
show config where name like '%log%'
show config where type='tikv' and name='log.level'

Modify TiKV configuration dynamically

Note

After dynamically changing TiKV configuration items, the TiKV configuration file is automatically updated. However, you also need to modify the corresponding configuration items by executing tiup edit-config; otherwise, operations such as upgrade and reload will overwrite your changes. For details of modifying configuration items, refer to Modify configuration using TiUP.
After executing tiup edit-config, you do not need to execute tiup reload.

When using the set config statement, you can modify the configuration of a single instance or of all instances according to the instance address or the component type.

Modify the configuration of all TiKV instances:

Note

It is recommended to wrap variable names in backticks.

set config tikv `split.qps-threshold`=1000;

Modify the configuration of a single TiKV instance:

set config "127.0.0.1:20180" `split.qps-threshold`=1000;

If the modification is successful, Query OK is returned:

Query OK, 0 rows affected (0.01 sec)

If an error occurs during the batch modification, a warning is returned:

set config tikv `log-level`='warn';

Query OK, 0 rows affected, 1 warning (0.04 sec)

show warnings;

+---------+------+---------------------------------------------------------------------------------------------------------------+
| Level   | Code | Message                                                                                                       |
+---------+------+---------------------------------------------------------------------------------------------------------------+
| Warning | 1105 | bad request to http://127.0.0.1:20180/config: fail to update, error: "config log-level can not be changed" |
+---------+------+---------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)

The batch modification does not guarantee atomicity. The modification might succeed on some instances, while failing on others. If you modify the configuration of the entire TiKV cluster using set tikv key=val, your modification might fail on some instances. You can use show warnings to check the result.

If some modifications fail, you need to re-execute the corresponding statement or modify each failed instance. If some TiKV instances cannot be accessed due to network issues or machine failure, modify these instances after they are recovered.

If a configuration item is successfully modified, the result is persisted in the configuration file, which will prevail in the subsequent operations. The names of some configuration items might conflict with TiDB reserved words, such as limit and key. For these configuration items, use backtick ` to enclose them. For example, `raftstore.raft-log-gc-size-limit`.

The following TiKV configuration items can be modified dynamically:

Configuration item	Description
`raftstore.raft-max-inflight-msgs`	The number of Raft logs to be confirmed. If this number is exceeded, the Raft state machine slows down log sending.
`raftstore.raft-log-gc-tick-interval`	The time interval at which the polling task of deleting Raft logs is scheduled
`raftstore.raft-log-gc-threshold`	The soft limit on the maximum allowable number of residual Raft logs
`raftstore.raft-log-gc-count-limit`	The hard limit on the allowable number of residual Raft logs
`raftstore.raft-log-gc-size-limit`	The hard limit on the allowable size of residual Raft logs
`raftstore.raft-max-size-per-msg`	The soft limit on the size of a single message packet that is allowed to be generated
`raftstore.raft-entry-max-size`	The hard limit on the maximum size of a single Raft log
`raftstore.raft-entry-cache-life-time`	The maximum remaining time allowed for the log cache in memory
`raftstore.split-region-check-tick-interval`	The time interval at which to check whether the Region split is needed
`raftstore.region-split-check-diff`	The maximum value by which the Region data is allowed to exceed before Region split
`raftstore.region-compact-check-interval`	The time interval at which to check whether it is necessary to manually trigger RocksDB compaction
`raftstore.region-compact-check-step`	The number of Regions checked at one time for each round of manual compaction
`raftstore.region-compact-min-tombstones`	The number of tombstones required to trigger RocksDB compaction
`raftstore.region-compact-tombstones-percent`	The proportion of tombstone required to trigger RocksDB compaction
`raftstore.pd-heartbeat-tick-interval`	The time interval at which a Region's heartbeat to PD is triggered
`raftstore.pd-store-heartbeat-tick-interval`	The time interval at which a store's heartbeat to PD is triggered
`raftstore.snap-mgr-gc-tick-interval`	The time interval at which the recycle of expired snapshot files is triggered
`raftstore.snap-gc-timeout`	The longest time for which a snapshot file is saved
`raftstore.lock-cf-compact-interval`	The time interval at which TiKV triggers a manual compaction for the Lock Column Family
`raftstore.lock-cf-compact-bytes-threshold`	The size at which TiKV triggers a manual compaction for the Lock Column Family
`raftstore.messages-per-tick`	The maximum number of messages processed per batch
`raftstore.max-peer-down-duration`	The longest inactive duration allowed for a peer
`raftstore.max-leader-missing-duration`	The longest duration allowed for a peer to be without a leader. If this value is exceeded, the peer verifies with PD whether it has been deleted.
`raftstore.abnormal-leader-missing-duration`	The normal duration allowed for a peer to be without a leader. If this value is exceeded, the peer is seen as abnormal and marked in metrics and logs.
`raftstore.peer-stale-state-check-interval`	The time interval to check whether a peer is without a leader
`raftstore.consistency-check-interval`	The time interval to check consistency (NOT recommended because it is not compatible with the garbage collection in TiDB)
`raftstore.raft-store-max-leader-lease`	The longest trusted period of a Raft leader
`raftstore.merge-check-tick-interval`	The time interval for merge check
`raftstore.cleanup-import-sst-interval`	The time interval to check expired SST files
`raftstore.local-read-batch-size`	The maximum number of read requests processed in one batch
`raftstore.hibernate-timeout`	The shortest wait duration before entering hibernation upon start. Within this duration, TiKV does not hibernate (not released).
`raftstore.apply-pool-size`	The number of threads in the pool that flushes data to the disk, which is the size of the Apply thread pool
`raftstore.store-pool-size`	The number of threads in the pool that processes Raft, which is the size of the Raftstore thread pool
`raftstore.apply-max-batch-size`	Raft state machines process data write requests in batches by the BatchSystem. This configuration item specifies the maximum number of Raft state machines that can execute the requests in one batch.
`raftstore.store-max-batch-size`	Raft state machines process requests for flushing logs into the disk in batches by the BatchSystem. This configuration item specifies the maximum number of Raft state machines that can process the requests in one batch.
`readpool.unified.max-thread-count`	The maximum number of threads in the thread pool that uniformly processes read requests, which is the size of the UnifyReadPool thread pool
`coprocessor.split-region-on-table`	Enables to split Region by table
`coprocessor.batch-split-limit`	The threshold of Region split in batches
`coprocessor.region-max-size`	The maximum size of a Region
`coprocessor.region-split-size`	The size of the newly split Region
`coprocessor.region-max-keys`	The maximum number of keys allowed in a Region
`coprocessor.region-split-keys`	The number of keys in the newly split Region
`pessimistic-txn.wait-for-lock-timeout`	The longest duration that a pessimistic transaction waits for the lock
`pessimistic-txn.wake-up-delay-duration`	The duration after which a pessimistic transaction is woken up
`pessimistic-txn.pipelined`	Determines whether to enable the pipelined pessimistic locking process
`pessimistic-txn.in-memory`	Determines whether to enable the in-memory pessimistic lock
`quota.foreground-cpu-time`	The soft limit on the CPU resources used by TiKV foreground to process read and write requests
`quota.foreground-write-bandwidth`	The soft limit on the bandwidth with which transactions write data
`quota.foreground-read-bandwidth`	The soft limit on the bandwidth with which transactions and the Coprocessor read data
`quota.max-delay-duration`	The maximum time that a single read or write request is forced to wait before it is processed in the foreground
`gc.ratio-threshold`	The threshold at which Region GC is skipped (the number of GC versions/the number of keys)
`gc.batch-keys`	The number of keys processed in one batch
`gc.max-write-bytes-per-sec`	The maximum bytes that can be written into RocksDB per second
`gc.enable-compaction-filter`	Whether to enable compaction filter
`gc.compaction-filter-skip-version-check`	Whether to skip the cluster version check of compaction filter (not released)
`{db-name}.max-total-wal-size`	The maximum size of total WAL
`{db-name}.max-background-jobs`	The number of background threads in RocksDB
`{db-name}.max-background-flushes`	The maximum number of flush threads in RocksDB
`{db-name}.max-open-files`	The total number of files that RocksDB can open
`{db-name}.compaction-readahead-size`	The size of `readahead` during compaction
`{db-name}.bytes-per-sync`	The rate at which OS incrementally synchronizes files to disk while these files are being written asynchronously
`{db-name}.wal-bytes-per-sync`	The rate at which OS incrementally synchronizes WAL files to disk while the WAL files are being written
`{db-name}.writable-file-max-buffer-size`	The maximum buffer size used in WritableFileWrite
`{db-name}.{cf-name}.block-cache-size`	The cache size of a block
`{db-name}.{cf-name}.write-buffer-size`	The size of a memtable
`{db-name}.{cf-name}.max-write-buffer-number`	The maximum number of memtables
`{db-name}.{cf-name}.max-bytes-for-level-base`	The maximum number of bytes at base level (L1)
`{db-name}.{cf-name}.target-file-size-base`	The size of the target file at base level
`{db-name}.{cf-name}.level0-file-num-compaction-trigger`	The maximum number of files at L0 that trigger compaction
`{db-name}.{cf-name}.level0-slowdown-writes-trigger`	The maximum number of files at L0 that trigger write stall
`{db-name}.{cf-name}.level0-stop-writes-trigger`	The maximum number of files at L0 that completely block write
`{db-name}.{cf-name}.max-compaction-bytes`	The maximum number of bytes written into disk per compaction
`{db-name}.{cf-name}.max-bytes-for-level-multiplier`	The default amplification multiple for each layer
`{db-name}.{cf-name}.disable-auto-compactions`	Enables or disables automatic compaction
`{db-name}.{cf-name}.soft-pending-compaction-bytes-limit`	The soft limit on the pending compaction bytes
`{db-name}.{cf-name}.hard-pending-compaction-bytes-limit`	The hard limit on the pending compaction bytes
`{db-name}.{cf-name}.titan.blob-run-mode`	The mode of processing blob files
`server.grpc-memory-pool-quota`	Limits the memory size that can be used by gRPC
`server.max-grpc-send-msg-len`	Sets the maximum length of a gRPC message that can be sent
`server.snap-max-write-bytes-per-sec`	Sets the maximum allowable disk bandwidth when processing snapshots
`server.concurrent-send-snap-limit`	Sets the maximum number of snapshots sent at the same time
`server.concurrent-recv-snap-limit`	Sets the maximum number of snapshots received at the same time
`server.raft-msg-max-batch-size`	Sets the maximum number of Raft messages that are contained in a single gRPC message
`storage.block-cache.capacity`	The size of shared block cache (supported since v4.0.3)
`storage.scheduler-worker-pool-size`	The number of threads in the Scheduler thread pool
`backup.num-threads`	The number of backup threads (supported since v4.0.3)
`split.qps-threshold`	The threshold to execute `load-base-split` on a Region. If the QPS of read requests for a Region exceeds `qps-threshold` for a consecutive period of time, this Region should be split.
`split.byte-threshold`	The threshold to execute `load-base-split` on a Region. If the traffic of read requests for a Region exceeds the `byte-threshold` for a consecutive period of time, this Region should be split.
`split.split-balance-score`	The parameter of `load-base-split`, which ensures the load of the two split Regions is as balanced as possible. The smaller the value is, the more balanced the load is. But setting it too small might cause split failure.
`split.split-contained-score`	The parameter of `load-base-split`. The smaller the value, the fewer cross-Region visits after Region split.
`cdc.min-ts-interval`	The time interval at which Resolved TS is forwarded
`cdc.old-value-cache-memory-quota`	The upper limit of memory occupied by the TiCDC Old Value entries
`cdc.sink-memory-quota`	The upper limit of memory occupied by TiCDC data change events
`cdc.incremental-scan-speed-limit`	The upper limit on the speed of incremental scanning for historical data
`cdc.incremental-scan-concurrency`	The maximum number of concurrent incremental scanning tasks for historical data

In the table above, parameters with the {db-name} or {db-name}.{cf-name} prefix are configurations related to RocksDB. The optional values of db-name are rocksdb and raftdb.

When db-name is rocksdb, the optional values of cf-name are defaultcf, writecf, lockcf, and raftcf.
When db-name is raftdb, the value of cf-name can be defaultcf.

For detailed parameter description, refer to TiKV Configuration File.

Modify PD configuration dynamically

Currently, PD does not support the separate configuration for each instance. All PD instances share the same configuration.

You can modify the PD configurations using the following statement:

set config pd `log.level`='info';

If the modification is successful, Query OK is returned:

Query OK, 0 rows affected (0.01 sec)

If a configuration item is successfully modified, the result is persisted in etcd instead of in the configuration file; the configuration in etcd will prevail in the subsequent operations. The names of some configuration items might conflict with TiDB reserved words. For these configuration items, use backtick ` to enclose them. For example, `schedule.leader-schedule-limit`.

The following PD configuration items can be modified dynamically:

Configuration item	Description
`log.level`	The log level
`cluster-version`	The cluster version
`schedule.max-merge-region-size`	Controls the size limit of `Region Merge` (in MiB)
`schedule.max-merge-region-keys`	Specifies the maximum numbers of the `Region Merge` keys
`schedule.patrol-region-interval`	Determines the frequency at which `replicaChecker` checks the health state of a Region
`schedule.split-merge-interval`	Determines the time interval of performing split and merge operations on the same Region
`schedule.max-snapshot-count`	Determines the maximum number of snapshots that a single store can send or receive at the same time
`schedule.max-pending-peer-count`	Determines the maximum number of pending peers in a single store
`schedule.max-store-down-time`	The downtime after which PD judges that the disconnected store cannot be recovered
`schedule.leader-schedule-policy`	Determines the policy of Leader scheduling
`schedule.leader-schedule-limit`	The number of Leader scheduling tasks performed at the same time
`schedule.region-schedule-limit`	The number of Region scheduling tasks performed at the same time
`schedule.replica-schedule-limit`	The number of Replica scheduling tasks performed at the same time
`schedule.merge-schedule-limit`	The number of the `Region Merge` scheduling tasks performed at the same time
`schedule.hot-region-schedule-limit`	The number of hot Region scheduling tasks performed at the same time
`schedule.hot-region-cache-hits-threshold`	Determines the threshold at which a Region is considered a hot spot
`schedule.high-space-ratio`	The threshold ratio below which the capacity of the store is sufficient
`schedule.low-space-ratio`	The threshold ratio above which the capacity of the store is insufficient
`schedule.tolerant-size-ratio`	Controls the `balance` buffer size
`schedule.enable-remove-down-replica`	Determines whether to enable the feature that automatically removes `DownReplica`
`schedule.enable-replace-offline-replica`	Determines whether to enable the feature that migrates `OfflineReplica`
`schedule.enable-make-up-replica`	Determines whether to enable the feature that automatically supplements replicas
`schedule.enable-remove-extra-replica`	Determines whether to enable the feature that removes extra replicas
`schedule.enable-location-replacement`	Determines whether to enable isolation level check
`schedule.enable-cross-table-merge`	Determines whether to enable cross-table merge
`schedule.enable-one-way-merge`	Enables one-way merge, which only allows merging with the next adjacent Region
`replication.max-replicas`	Sets the maximum number of replicas
`replication.location-labels`	The topology information of a TiKV cluster
`replication.enable-placement-rules`	Enables Placement Rules
`replication.strictly-match-label`	Enables the label check
`pd-server.use-region-storage`	Enables independent Region storage
`pd-server.max-gap-reset-ts`	Sets the maximum interval of resetting timestamp (BR)
`pd-server.key-type`	Sets the cluster key type
`pd-server.metric-storage`	Sets the storage address of the cluster metrics
`pd-server.dashboard-address`	Sets the dashboard address
`replication-mode.replication-mode`	Sets the backup mode

For detailed parameter description, refer to PD Configuration File.

Modify TiDB configuration dynamically

Currently, the method of changing TiDB configuration is different from that of changing TiKV and PD configurations. You can modify TiDB configuration by using system variables.

The following example shows how to dynamically modify slow-threshold by using the tidb_slow_log_threshold variable.

The default value of slow-threshold is 300 ms. You can set it to 200 ms by using tidb_slow_log_threshold.

set tidb_slow_log_threshold = 200;

Query OK, 0 rows affected (0.00 sec)

select @@tidb_slow_log_threshold;

+---------------------------+
| @@tidb_slow_log_threshold |
+---------------------------+
| 200                       |
+---------------------------+
1 row in set (0.00 sec)

The following TiDB configuration items can be modified dynamically:

Configuration item	SQL variable
`instance.tidb_enable_slow_log`	`tidb_enable_slow_log`
`instance.tidb_slow_log_threshold`	`tidb_slow_log_threshold`
`instance.tidb_expensive_query_time_threshold`	`tidb_expensive_query_time_threshold`

Modify TiFlash configuration dynamically

Currently, you can modify the TiFlash configuration max_threads by using the system variable tidb_max_tiflash_threads, which specifies the maximum concurrency for TiFlash to execute a request.

The default value of tidb_max_tiflash_threads is -1, indicating that this system variable is invalid and depends on the setting of the TiFlash configuration file. You can set max_threads to 10 by using tidb_max_tiflash_threads:

set tidb_max_tiflash_threads = 10;

Query OK, 0 rows affected (0.00 sec)

select @@tidb_max_tiflash_threads;

+----------------------------+
| @@tidb_max_tiflash_threads |
+----------------------------+
| 10                         |
+----------------------------+
1 row in set (0.00 sec)