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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.


  • 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.


  • Specifies the operation when out-of-memory occurs in TiDB
  • Default value: log
  • The valid options are log and cancel. log only prints the log without actual processing. cancel" cancels the operation and outputs the log.


  • The maximum memory available for a single SQL statement
  • Default value: 34359738368
  • Requests that require more memory than this value are handled based on the behavior defined by oom-action.


  • Determines whether to enable the data fetch mode of streaming in Coprocessor
  • Default value: false


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

  • Default value: 2

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


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


  • 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.


  • 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


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


  • 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.


  • 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}.


  • 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.


Configuration items related to log


  • Specifies the log output format
  • Available values: json, text, console
  • Default value: text


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


  • 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


  • 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


  • 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.


  • The maximum length of SQL output
  • Default value: 2048
  • When the length of the statement is longer than query-log-max-len, the statement is truncated to output.


Configuration items related to log files


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


  • The size limit of the log file
  • Default value: 300MB
  • The maximum size is 4GB.


  • 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.


  • 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.


  • Determines whether to create a new log file every day
  • Default value: true
  • If you set the parameter to true, a new log file is created every day. If you set it to false, the log is output to a single log file.


Configuration items related to security


  • 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.


  • 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


  • 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


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


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


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


  • Determines whether to skip permission check
  • Default value: false


Configuration items related to performance


  • 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.


  • 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.


  • 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 optimistic transaction. If you use the pessimistic transaction, the number of statements in a transaction is not limited by this configuration.


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


  • 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.


  • 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


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


  • The probability that TiDB collects the feedback statistics of each query
  • Default value: 0.05
  • TiDB collects the feedback of each query at the probability of feedback-probability, to update statistics


  • 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


  • 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.


  • Sets the priority for all statements
  • Default: NO_PRIORITY


The Plan Cache configuration of the PREPARE statement


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


  • The number of cached statements
  • Default value: 100


  • It is used to prevent performance.max-memory from being exceeded. When max-proc * (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



  • The maximum number of connections established with each TiKV
  • Default value: 16


  • 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


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


  • 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.


  • The maximum execution time allowed for a single transaction
  • Default value: 590
  • unit: second


  • 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


  • 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


  • 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.


  • 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


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


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


  • 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


Configurations related to TiDB Binlog


  • Enables or disables binlog
  • Default value: false


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


  • 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.


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


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


Configuration related to the status of TiDB service


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


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

stmt-summary New in v3.0.4

Configurations related to the events_statement_summary_by_digest table


  • The maximum number of SQL categories allowed to be saved in the events_statement_summary_by_digest table.
  • Default value: 100


  • The longest display length for the DIGEST_TEXT and QUERY_SAMPLE_TEXT columns in the events_statement_summary_by_digest table.
  • Default value: 4096




  • The max number of retries of each statement in pessimistic transactions. Exceeding this limit results in error.
  • Default value: 256


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

allow-auto-random New in v3.1.0

  • Determines whether to allow using AUTO_RANDOM.
  • Default value: false
  • By default, TiDB does not support using AUTO_RANDOM. When the value is true, you cannot set alter-primary-key to true at the same time.
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