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TiDB Configuration File

The TiDB configuration file supports more options than command-line parameters. You can download the default configuration file config.toml.example and rename it to config.toml. This document describes only the options that are not involved in command line options.

split-table

  • Determines whether to create a separate Region for each table.
  • Default value: true
  • It is recommended to set it to false if you need to create a large number of tables.

token-limit

  • The number of sessions that can execute requests concurrently.
  • Default value: 1000

mem-quota-query

  • The maximum memory available for a single SQL statement.
  • Default value: 1073741824 (in bytes)
  • Note: When you upgrade the cluster from v2.0.x or v3.0.x to v4.0.9 or later versions, the default value of this configuration is 34359738368.
  • Requests that require more memory than this value are handled based on the behavior defined by oom-action.
  • This value is the initial value of the system variable tidb_mem_quota_query.

oom-use-tmp-storage

  • Controls whether to enable the temporary storage for some operators when a single SQL statement exceeds the memory quota specified by mem-quota-query.
  • Default value: true

tmp-storage-path

  • Specifies the temporary storage path for some operators when a single SQL statement exceeds the memory quota specified by mem-quota-query.
  • Default value: <temporary directory of OS>/<OS user ID>_tidb/MC4wLjAuMDo0MDAwLzAuMC4wLjA6MTAwODA=/tmp-storage. MC4wLjAuMDo0MDAwLzAuMC4wLjA6MTAwODA= is the Base64 encoding result of <host>:<port>/<statusHost>:<statusPort>.
  • This configuration takes effect only when oom-use-tmp-storage is true.

tmp-storage-quota

  • Specifies the quota for the storage in tmp-storage-path. The unit is byte.
  • When a single SQL statement uses a temporary disk and the total volume of the temporary disk of the TiDB server exceeds this configuration value, the current SQL operation is cancelled and the Out of Global Storage Quota! error is returned.
  • When the value of this configuration is smaller than 0, the above check and limit do not apply.
  • Default value: -1
  • When the remaining available storage in tmp-storage-path is lower than the value defined by tmp-storage-quota, the TiDB server reports an error when it is started, and exits.

oom-action

  • Specifies what operation TiDB performs when a single SQL statement exceeds the memory quota specified by mem-quota-query and cannot be spilled over to disk.
  • Default value: "cancel" (In TiDB v4.0.2 and earlier versions, the default value is "log")
  • The valid options are "log" and "cancel". When oom-action="log", it prints the log only. When oom-action="cancel", it cancels the operation and outputs the log.

lower-case-table-names

  • Configures the value of the lower-case-table-names system variable.

  • Default value: 2

  • For details, see the MySQL description of this variable.

lease

  • The timeout of the DDL lease.
  • Default value: 45s
  • Unit: second

compatible-kill-query

  • Determines whether to set the KILL statement to be MySQL compatible.
  • Default value: false
  • The behavior of KILL xxx in TiDB differs from the behavior in MySQL. TiDB requires the TIDB keyword, namely, KILL TIDB xxx. If compatible-kill-query is set to true, the TIDB keyword is not needed.
  • This distinction is important because the default behavior of the MySQL command-line client, when the user hits Ctrl+C, is to create a new connection to the backend and execute the KILL statement in that new connection. If a load balancer or proxy has sent the new connection to a different TiDB server instance than the original session, the wrong session could be terminated, which could cause interruption to applications using the cluster. Enable compatible-kill-query only if you are certain that the connection you refer to in your KILL statement is on the same server to which you send the KILL statement.

check-mb4-value-in-utf8

  • Determines whether to enable the utf8mb4 character check. When this feature is enabled, if the character set is utf8 and the mb4 characters are inserted in utf8, an error is returned.
  • Default value: false

treat-old-version-utf8-as-utf8mb4

  • Determines whether to treat the utf8 character set in old tables as utf8mb4.
  • Default value: true

alter-primary-key

  • Determines whether to add or remove the primary key constraint to or from a column.
  • Default value: false
  • With this default setting, adding or removing the primary key constraint is not supported. You can enable this feature by setting alter-primary-key to true. However, if a table already exists before the switch is on, and the data type of its primary key column is an integer, dropping the primary key from the column is not possible even if you set this configuration item to true.

server-version

  • Modifies the version string returned by TiDB in the following situations:
    • When the built-in VERSION() function is used.
    • When TiDB establishes the initial connection to the client and returns the initial handshake packet with version string of the server. For details, see MySQL Initial Handshake Packet.
  • Default value: ""
  • By default, the format of the TiDB version string is 5.7.${mysql_latest_minor_version}-TiDB-${tidb_version}.

repair-mode

  • Determines whether to enable the untrusted repair mode. When the repair-mode is set to true, bad tables in the repair-table-list cannot be loaded.
  • Default value: false
  • The repair syntax is not supported by default. This means that all tables are loaded when TiDB is started.

repair-table-list

  • repair-table-list is only valid when repair-mode is set to true. repair-table-list is a list of bad tables that need to be repaired in an instance. An example of the list is: ["db.table1","db.table2"...].
  • Default value: []
  • The list is empty by default. This means that there are no bad tables that need to be repaired.

new_collations_enabled_on_first_bootstrap

  • Enables or disables the new collation support.
  • Default value: false
  • Note: This configuration takes effect only for the TiDB cluster that is first initialized. After the initialization, you cannot use this configuration item to enable or disable the new collation support. When a TiDB cluster is upgraded to v4.0, because the cluster has been initialized before, both true and false values of this configuration item are taken as false.

max-server-connections

  • The maximum number of concurrent client connections allowed in TiDB. It is used to control resources.
  • Default value: 0
  • By default, TiDB does not set limit on the number of concurrent client connections. When the value of this configuration item is greater than 0 and the number of actual client connections reaches this value, the TiDB server rejects new client connections.

max-index-length

  • Sets the maximum allowable length of the newly created index.
  • Default value: 3072
  • Unit: byte
  • Currently, the valid value range is [3072, 3072*4]. MySQL and TiDB (version < v3.0.11) do not have this configuration item, but both limit the length of the newly created index. This limit in MySQL is 3072. In TiDB (version =< 3.0.7), this limit is 3072*4. In TiDB (3.0.7 < version < 3.0.11), this limit is 3072. This configuration is added to be compatible with MySQL and earlier versions of TiDB.

enable-telemetry New in v4.0.2

  • Enables or disables the telemetry collection in TiDB.
  • Default value: true
  • When this configuration is set to false on all TiDB instances, the telemetry collection in TiDB is disabled and the tidb_enable_telemetry system variable does not take effect. See Telemetry for details.

enable-forwarding New in v5.0.0

  • Controls whether the PD client and TiKV client in TiDB forward requests to the leader via the followers in the case of possible network isolation.
  • Default value: false
  • If the environment might have isolated network, enabling this parameter can reduce the window of service unavailability.
  • If you cannot accurately determine whether isolation, network interruption, or downtime has occurred, using this mechanism has the risk of misjudgment and causes reduced availability and performance. If network failure has never occurred, it is not recommended to enable this parameter.

enable-table-lock New in v4.0.0

  • Controls whether to enable the table lock feature.
  • Default value: false
  • The table lock is used to coordinate concurrent access to the same table among multiple sessions. Currently, the READ, WRITE, and WRITE LOCAL lock types are supported. When the configuration item is set to false, executing the LOCK TABLE or UNLOCK TABLE statement does not take effect and returns the "LOCK/UNLOCK TABLES is not supported" warning.

Log

Configuration items related to log.

level

  • Specifies the log output level.
  • Value options: debug, info, warn, error, and fatal.
  • Default value: info

format

  • Specifies the log output format.
  • Value options: json, text and console.
  • Default value: text

enable-timestamp

  • Determines whether to enable timestamp output in the log.
  • Default value: true
  • If you set the value to false, the log does not output timestamp.

enable-slow-log

  • Determines whether to enable the slow query log.
  • Default value: true
  • To enable the slow query log, set enable-slow-log to true. Otherwise, set it to false.

slow-query-file

  • The file name of the slow query log.
  • Default value: tidb-slow.log
  • The format of the slow log is updated in TiDB v2.1.8, so the slow log is output to the slow log file separately. In versions before v2.1.8, this variable is set to "" by default.
  • After you set it, the slow query log is output to this file separately.

slow-threshold

  • Outputs the threshold value of consumed time in the slow log.
  • Default value: 300ms
  • If the value in a query is larger than the default value, it is a slow query and is output to the slow log.

record-plan-in-slow-log

  • Determines whether to record execution plans in the slow log.
  • Default value: 1
  • 0 means to disable, and 1 (by default) means to enable. The value of this parameter is the initial value of the tidb_record_plan_in_slow_log system variable.

expensive-threshold

  • Outputs the threshold value of the number of rows for the expensive operation.
  • Default value: 10000
  • When the number of query rows (including the intermediate results based on statistics) is larger than this value, it is an expensive operation and outputs log with the [EXPENSIVE_QUERY] prefix.

query-log-max-len

  • The maximum length of SQL output.
  • Default value: 4096
  • When the length of the statement is longer than query-log-max-len, the statement is truncated to output.

log.file

Configuration items related to log files.

filename

  • The file name of the general log file.
  • Default value: ""
  • If you set it, the log is output to this file.

max-size

  • The size limit of the log file.
  • Default value: 300
  • Unit: MB
  • The maximum value is 4096.

max-days

  • The maximum number of days that the log is retained.
  • Default value: 0
  • The log is retained by default. If you set the value, the expired log is cleaned up after max-days.

max-backups

  • The maximum number of retained logs.
  • Default value: 0
  • All the log files are retained by default. If you set it to 7, seven log files are retained at maximum.

Security

Configuration items related to security.

ssl-ca

  • The file path of the trusted CA certificate in the PEM format.
  • Default value: ""
  • If you set this option and --ssl-cert, --ssl-key at the same time, TiDB authenticates the client certificate based on the list of trusted CAs specified by this option when the client presents the certificate. If the authentication fails, the connection is terminated.
  • If you set this option but the client does not present the certificate, the secure connection continues without client certificate authentication.

ssl-cert

  • The file path of the SSL certificate in the PEM format.
  • Default value: ""
  • If you set this option and --ssl-key at the same time, TiDB allows (but not forces) the client to securely connect to TiDB using TLS.
  • If the specified certificate or private key is invalid, TiDB starts as usual but cannot receive secure connection.

ssl-key

  • The file path of the SSL certificate key in the PEM format, that is, the private key of the certificate specified by --ssl-cert.
  • Default value: ""
  • Currently, TiDB does not support loading the private keys protected by passwords.

cluster-ssl-ca

  • The CA root certificate used to connect TiKV or PD with TLS.
  • Default value: ""

cluster-ssl-cert

  • The path of the SSL certificate file used to connect TiKV or PD with TLS.
  • Default value: ""

cluster-ssl-key

  • The path of the SSL private key file used to connect TiKV or PD with TLS.
  • Default value: ""

Performance

Configuration items related to performance.

max-procs

  • The number of CPUs used by TiDB.
  • Default value: 0
  • The default 0 indicates using all the CPUs on the machine. You can also set it to n, and then TiDB uses n CPUs.

max-memory

  • The maximum memory limit for the Prepared Least Recently Used (LRU) caching. If this value exceeds performance.max-memory * (1 - prepared-plan-cache.memory-guard-ratio), the elements in the LRU are removed.
  • Default value: 0
  • This configuration only takes effect when prepared-plan-cache.enabled is true. When the size of the LRU is greater than prepared-plan-cache.capacity, the elements in the LRU are also removed.

server-memory-quota New in v4.0.9

  • The memory usage limit of tidb-server instances.
  • Default value: 0 (in bytes), which means no memory limit.

memory-usage-alarm-ratio New in v4.0.9

  • TiDB triggers an alarm when the memory usage of tidb-server instance exceeds a certain threshold. The valid value for this configuration item ranges from 0 to 1. If it is configured as 0 or 1, this alarm feature is disabled.
  • Default value: 0.8
  • When the memory usage alarm is enabled, if server-memory-quota is not set, then the threshold of memory usage is the `memory-usage-alarm-ratio` value * the system memory size; if server-memory-quota is set to a value greater than 0, then the threshold of memory usage is the `memory-usage-alarm-ratio` value * the `server-memory-quota` value.
  • When TiDB detects that the memory usage of the tidb-server instance exceeds the threshold, it considers that there might be a risk of OOM. Therefore, it records ten SQL statements with the highest memory usage, ten SQL statements with the longest running time, and the heap profile among all SQL statements currently being executed to the directory tmp-storage-path/record and outputs a log containing the keyword tidb-server has the risk of OOM.
  • The value of this configuration item is the initial value of the system variable tidb_memory_usage_alarm_ratio.

max-txn-ttl

  • The longest time that a single transaction can hold locks. If this time is exceeded, the locks of a transaction might be cleared by other transactions so that this transaction cannot be successfully committed.
  • Default value: 600000
  • Unit: Millisecond
  • The transaction that holds locks longer than this time can only be committed or rolled back. The commit might not be successful.

committer-concurrency

  • The number of goroutines for requests related to executing commit in the commit phase of the single transaction.
  • Default value: 16
  • If the transaction to commit is too large, the waiting time for the flow control queue when the transaction is committed might be too long. In this situation, you can increase the configuration value to speed up the commit.

stmt-count-limit

  • The maximum number of statements allowed in a single TiDB transaction.
  • Default value: 5000
  • If a transaction does not roll back or commit after the number of statements exceeds stmt-count-limit, TiDB returns the statement count 5001 exceeds the transaction limitation, autocommit = false error. This configuration takes effect only in the retriable optimistic transaction. If you use the pessimistic transaction or have disabled the transaction retry, the number of statements in a transaction is not limited by this configuration.

txn-entry-size-limit New in v4.0.10

  • The size limit of a single row of data in TiDB.
  • Default value: 6291456 (in bytes)
  • The size limit of a single key-value record in a transaction. If the size limit is exceeded, TiDB returns the entry too large error. The maximum value of this configuration item does not exceed 125829120 (120 MB).
  • Note that TiKV has a similar limit. If the data size of a single write request exceeds raft-entry-max-size, which is 8 MB by default, TiKV refuses to process this request. When a table has a row of large size, you need to modify both configurations at the same time.

txn-total-size-limit

  • The size limit of a single transaction in TiDB.
  • Default value: 104857600 (in bytes)
  • In a single transaction, the total size of key-value records cannot exceed this value. The maximum value of this parameter is 10737418240 (10 GB). Note that if you have used the binlog to serve the downstream consumer Kafka (such as the arbiter cluster), the value of this parameter must be no more than 1073741824 (1 GB). This is because 1 GB is the upper limit of a single message size that Kafka can process. Otherwise, an error is returned if this limit is exceeded.

tcp-keep-alive

  • Determines whether to enable keepalive in the TCP layer.
  • Default value: true

cross-join

  • Default value: true
  • TiDB supports executing the JOIN statement without any condition (the WHERE field) of both sides tables by default; if you set the value to false, the server refuses to execute when such a JOIN statement appears.

stats-lease

  • The time interval of reloading statistics, updating the number of table rows, checking whether it is needed to perform the automatic analysis, using feedback to update statistics and loading statistics of columns.
  • Default value: 3s
    • At intervals of stats-lease time, TiDB checks the statistics for updates and updates them to the memory if updates exist.
    • At intervals of 20 * stats-lease time, TiDB updates the total number of rows generated by DML and the number of modified rows to the system table.
    • At intervals of stats-lease, TiDB checks for tables and indexes that need to be automatically analyzed.
    • At intervals of stats-lease, TiDB checks for column statistics that need to be loaded to the memory.
    • At intervals of 200 * stats-lease, TiDB writes the feedback cached in the memory to the system table.
    • At intervals of 5 * stats-lease, TiDB reads the feedback in the system table, and updates the statistics cached in the memory.
  • When stats-lease is set to 0s, TiDB periodically reads the feedback in the system table, and updates the statistics cached in the memory every three seconds. But TiDB no longer automatically modifies the following statistics-related system tables:
    • mysql.stats_meta: TiDB no longer automatically records the number of table rows that are modified by the transaction and updates it to this system table.
    • mysql.stats_histograms/mysql.stats_buckets and mysql.stats_top_n: TiDB no longer automatically analyzes and proactively updates statistics.
    • mysql.stats_feedback: TiDB no longer updates the statistics of the tables and indexes according to a part of statistics returned by the queried data.

run-auto-analyze

  • Determines whether TiDB executes automatic analysis.
  • Default value: true

feedback-probability

  • The probability that TiDB collects the feedback statistics of each query.
  • Default value: 0
  • This feature is disabled by default, and it is not recommended to enable this feature. If it is enabled, TiDB collects the feedback of each query at the probability of feedback-probability, to update statistics.

query-feedback-limit

  • The maximum pieces of query feedback that can be cached in memory. Extra pieces of feedback that exceed this limit are discarded.
  • Default value: 1024

pseudo-estimate-ratio

  • The ratio of (number of modified rows)/(total number of rows) in a table. If the value is exceeded, the system assumes that the statistics have expired and the pseudo statistics will be used.
  • Default value: 0.8
  • The minimum value is 0 and the maximum value is 1.

force-priority

  • Sets the priority for all statements.
  • Default: NO_PRIORITY
  • Optional values: NO_PRIORITY, LOW_PRIORITY, HIGH_PRIORITY and DELAYED.

distinct-agg-push-down

  • Determines whether the optimizer executes the operation that pushes down the aggregation function with Distinct (such as select count(distinct a) from t) to Coprocessors.
  • Default: false
  • This variable is the initial value of the system variable tidb_opt_distinct_agg_push_down.

nested-loop-join-cache-capacity

  • The maximum memory usage for the Least Recently Used (LRU) algorithm of the nested loop join cache (in bytes).
  • Default value: 20971520
  • When nested-loop-join-cache-capacity is set to 0, nested loop join cache is disabled by default. When the LRU size is larger than the value of nested-loop-join-cache-capacity, the elements in the LRU are removed.

prepared-plan-cache

The Plan Cache configuration of the PREPARE statement.

enabled

  • Determines whether to enable Plan Cache of the PREPARE statement.
  • Default value: false

capacity

  • The number of cached statements.
  • Default value: 100
  • The type is UINT. Values less than 0 are converted to large integers.

memory-guard-ratio

  • It is used to prevent performance.max-memory from being exceeded. When max-memory * (1 - prepared-plan-cache.memory-guard-ratio) is exceeded, the elements in the LRU are removed.
  • Default value: 0.1
  • The minimum value is 0; the maximum value is 1.

tikv-client

grpc-connection-count

  • The maximum number of connections established with each TiKV.
  • Default value: 4

grpc-keepalive-time

  • The keepalive time interval of the RPC connection between TiDB and TiKV nodes. If there is no network packet within the specified time interval, the gRPC client executes ping command to TiKV to see if it is alive.
  • Default: 10
  • unit: second

grpc-keepalive-timeout

  • The timeout of the RPC keepalive check between TiDB and TiKV nodes.
  • Default value: 3
  • unit: second

commit-timeout

  • The maximum timeout when executing a transaction commit.
  • Default value: 41s
  • It is required to set this value larger than twice of the Raft election timeout.

max-batch-size

  • The maximum number of RPC packets sent in batch. If the value is not 0, the BatchCommands API is used to send requests to TiKV, and the RPC latency can be reduced in the case of high concurrency. It is recommended that you do not modify this value.
  • Default value: 128

max-batch-wait-time

  • Waits for max-batch-wait-time to encapsulate the data packets into a large packet in batch and send it to the TiKV node. It is valid only when the value of tikv-client.max-batch-size is greater than 0. It is recommended not to modify this value.
  • Default value: 0
  • unit: nanoseconds

batch-wait-size

  • The maximum number of packets sent to TiKV in batch. It is recommended not to modify this value.
  • Default value: 8
  • If the value is 0, this feature is disabled.

overload-threshold

  • The threshold of the TiKV load. If the TiKV load exceeds this threshold, more batch packets are collected to relieve the pressure of TiKV. It is valid only when the value of tikv-client.max-batch-size is greater than 0. It is recommended not to modify this value.
  • Default value: 200

tikv-client.copr-cache New in v4.0.0

This section introduces configuration items related to the Coprocessor Cache feature.

enable

  • Determines whether to enable Coprocessor Cache.
  • Default value: false (which means that Coprocessor Cache is disabled by default)

capacity-mb

  • The total size of the cached data. When the cache space is full, old cache entries are evicted.
  • Default value: 1000.0
  • Unit: MB
  • Type: Float

admission-max-result-mb

  • Specifies the largest single push-down calculation result set that can be cached. If the result set of a single push-down calculation returned on the Coprocessor is less than the result set specified by this parameter, the result set is cached. Increasing this value means that more types of push-down requests are cached, but also cause the cache space to be occupied more easily. Note that the size of each push-down calculation result set is generally smaller than the size of the Region. Therefore, it is meaningless to set this value far beyond the size of a Region.
  • Default value: 10.0
  • Unit: MB
  • Type: Float

admission-min-process-ms

  • Specifies the minimum calculation time for a single push-down calculation result set that can be cached. If the calculation time of a single push-down calculation on the Coprocessor is less than the time specified by this parameter, the result set is not cached. Requests that are processed quickly do not need to be cached, and only the requests that take a long time to process need to be cached, which makes the cache less likely to be evicted.
  • Default value: 5
  • Unit: ms

admission-max-ranges New in v4.0.8

  • Specifies the maximum number of ranges in a single push-down calculation result set that can be cached. If the push-down calculation has more ranges than the number specified by this configuration, the result set will not be cached. Generally, when there are too many ranges, the extra calculation overhead of parsing the range brought by Coprocessor Cache is large.
  • Default value: 500
  • Type: uint

txn-local-latches

Configuration related to the transaction latch. It is recommended to enable it when many local transaction conflicts occur.

enable

  • Determines whether to enable the memory lock of transactions.
  • Default value: false

capacity

  • The number of slots corresponding to Hash, which automatically adjusts upward to an exponential multiple of 2. Each slot occupies 32 Bytes of memory. If set too small, it might result in slower running speed and poor performance in the scenario where data writing covers a relatively large range (such as importing data).
  • Default value: 2048000

binlog

Configurations related to TiDB Binlog.

enable

  • Enables or disables binlog.
  • Default value: false

write-timeout

  • The timeout of writing binlog into Pump. It is not recommended to modify this value.
  • Default: 15s
  • unit: second

ignore-error

  • Determines whether to ignore errors occurred in the process of writing binlog into Pump. It is not recommended to modify this value.
  • Default value: false
  • When the value is set to true and an error occurs, TiDB stops writing binlog and add 1 to the count of the tidb_server_critical_error_total monitoring item. When the value is set to false, the binlog writing fails and the entire TiDB service is stopped.

binlog-socket

  • The network address to which binlog is exported.
  • Default value: ""

strategy

  • The strategy of Pump selection when binlog is exported. Currently, only the hash and range methods are supported.
  • Default value: range

status

Configuration related to the status of TiDB service.

report-status

  • Enables or disables the HTTP API service.
  • Default value: true

record-db-qps

  • Determines whether to transmit the database-related QPS metrics to Prometheus.
  • Default value: false

stmt-summary New in v3.0.4

Configurations related to statement summary tables.

max-stmt-count

  • The maximum number of SQL categories allowed to be saved in statement summary tables.
  • Default value: Before v4.0.14, the default value is 200. Since v4.0.14, the default value is 3000.

max-sql-length

  • The longest display length for the DIGEST_TEXT and QUERY_SAMPLE_TEXT columns in statement summary tables.
  • Default value: 4096

pessimistic-txn

enable

max-retry-count

  • The maximum number of retries of each statement in pessimistic transactions. If the number of retries exceeds this limit, an error occurs.
  • Default value: 256

experimental

The experimental section describes configurations related to the experimental features of TiDB. This section is introduced since v3.1.0.

allow-expression-index New in v4.0.0

  • Determines whether to create the expression index.
  • Default value: false
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