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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 (for example, more than 100 thousand tables).

tidb-max-reuse-chunk New in v6.4.0

  • Controls the maximum cached chunk objects of chunk allocation. Setting this configuration item to too large a value might increase the risk of OOM.
  • Default value: 64
  • Minimum value: 0
  • Maximum value: 2147483647

tidb-max-reuse-column New in v6.4.0

  • Controls the maximum cached column objects of chunk allocation. Setting this configuration item to too large a value might increase the risk of OOM.
  • Default value: 256
  • Minimum value: 0
  • Maximum value: 2147483647

token-limit

  • The number of sessions that can execute requests concurrently.
  • Type: Integer
  • Default value: 1000
  • Minimum value: 1
  • Maximum value: 1048576

temp-dir New in v6.3.0

  • File system location used by TiDB to store temporary data. If a feature requires local storage in TiDB nodes, TiDB stores the corresponding temporary data in this location.
  • When creating an index, if tidb_ddl_enable_fast_reorg is enabled, data that needs to be backfilled for a newly created index will be at first stored in the TiDB local temporary directory, and then imported into TiKV in batches, thus accelerating the index creation.
  • When IMPORT INTO is used to import data, the sorted data is first stored in the TiDB local temporary directory, and then imported into TiKV in batches.
  • Default value: "/tmp/tidb"

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 the system variable tidb_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 the system variable tidb_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 the system variable tidb_enable_tmp_storage_on_oom is ON.

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.

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
  • compatible-kill-query takes effect only when enable-global-kill is set to false.
  • When enable-global-kill is false, compatible-kill-query controls whether you need to append the TIDB keyword when killing a query.
    • When compatible-kill-query is false, the behavior of KILL xxx in TiDB is different from that in MySQL. To kill a query in TiDB, you need to append the TIDB keyword, such as KILL TIDB xxx.
    • When compatible-kill-query is true, to kill a query in TiDB, there is no need to append the TIDB keyword. It is STRONGLY NOT RECOMMENDED to set compatible-kill-query to true in your configuration file UNLESS you are certain that clients will be always connected to the same TiDB instance. This is because pressing Control+C in the default MySQL client opens a new connection in which KILL is executed. If there is a proxy between the client and the TiDB cluster, the new connection might be routed to a different TiDB instance, which possibly kills a different session by mistake.
  • When enable-global-kill is true, KILL xxx and KILL TIDB xxx have the same effect.
  • For more information about the KILL statement, see KILL [TIDB].

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
  • Since v6.1.0, whether to enable the utf8mb4 character check is determined by the TiDB configuration item instance.tidb_check_mb4_value_in_utf8 or the system variable tidb_check_mb4_value_in_utf8. check-mb4-value-in-utf8 still takes effect. But if both check-mb4-value-in-utf8 and instance.tidb_check_mb4_value_in_utf8 are set, the latter takes effect.

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 (Deprecated)

  • 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 8.0.11-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: true
  • 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.

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.
  • Since v6.2.0, the TiDB configuration item instance.max_connections or the system variable max_connections is used to set the maximum number of concurrent client connections allowed in TiDB. max-server-connections still takes effect. But if max-server-connections and instance.max_connections are set at the same time, the latter takes effect.

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.

table-column-count-limit New in v5.0

  • Sets the limit on the number of columns in a single table.
  • Default value: 1017
  • Currently, the valid value range is [1017, 4096].

index-limit New in v5.0

  • Sets the limit on the number of indexes in a single table.
  • Default value: 64
  • Currently, the valid value range is [64, 512].

enable-telemetry New in v4.0.2 and deprecated in v8.1.0

  • Before v8.1.0, this configuration item controls whether to enable telemetry collection in a TiDB instance.
  • Default value: false

deprecate-integer-display-length

  • Deprecates the display width for integer types when this configuration item is set to true.
  • Default value: false

enable-tcp4-only New in v5.0

  • Enables or disables listening on TCP4 only.
  • Default value: false
  • Enabling this option is useful when TiDB is used with LVS for load balancing because the real client IP from the TCP header can be correctly parsed by the "tcp4" protocol.

enable-enum-length-limit New in v5.0

  • Determines whether to limit the maximum length of a single ENUM element and a single SET element.
  • Default value: true
  • When this configuration value is true, the maximum length of a single ENUM element and a single SET element is 255 characters, which is compatible with MySQL 8.0. When this configuration value is false, there is no limit on the length of a single element, which is compatible with TiDB (earlier than v5.0).

graceful-wait-before-shutdown New in v5.0

  • Specifies the number of seconds that TiDB waits when you shut down the server, which allows the clients to disconnect.
  • Default value: 0
  • When TiDB is waiting for shutdown (in the grace period), the HTTP status will indicate a failure, which allows the load balancers to reroute traffic.

enable-global-kill New in v6.1.0

  • Controls whether to enable the Global Kill (terminating queries or connections across instances) feature.
  • Default value: true
  • When the value is true, both KILL and KILL TIDB statements can terminate queries or connections across instances so you do not need to worry about erroneously terminating queries or connections. When you use a client to connect to any TiDB instance and execute the KILL or KILL TIDB statement, the statement will be forwarded to the target TiDB instance. If there is a proxy between the client and the TiDB cluster, the KILL and KILL TIDB statements will also be forwarded to the target TiDB instance for execution.
  • Starting from v7.3.0, you can terminate a query or connection using the MySQL command line Control+C when both enable-global-kill and enable-32bits-connection-id are set to true. For more information, see KILL.

enable-32bits-connection-id New in v7.3.0

  • Controls whether to enable the 32-bit connection ID feature.
  • Default value: true
  • When both this configuration item and enable-global-kill are set to true, TiDB generates 32-bit connection IDs. This enables you to terminate queries or connections by the MySQL command-line Control+C.

initialize-sql-file New in v6.6.0

  • Specifies the SQL script to be executed when the TiDB cluster is started for the first time.
  • Default value: ""
  • All SQL statements in this script are executed with the highest privilege without any privilege check. If the specified SQL script fails to execute, the TiDB cluster might fail to start.
  • This configuration item is used to perform such operations as modifying the value of a system variable, creating a user, or granting privileges.

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 TABLES or UNLOCK TABLES statement does not take effect and returns the "LOCK/UNLOCK TABLES is not supported" warning. For more information, see LOCK TABLES and UNLOCK TABLES.

labels

  • Specify server labels. For example, { zone = "us-west-1", dc = "dc1", rack = "rack1", host = "tidb1" }.
  • Default value: {}

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 and text.
  • Default value: text

enable-timestamp

  • Determines whether to enable timestamp output in the log.
  • Default value: null
  • 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.
  • Since v6.1.0, whether to enable slow query log is determined by the TiDB configuration item instance.tidb_enable_slow_log or the system variable tidb_enable_slow_log. enable-slow-log still takes effect. But if enable-slow-log and instance.tidb_enable_slow_log are set at the same time, the latter takes effect.

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: 300
  • Unit: Milliseconds
  • When the time consumed by a query is larger than this value, this query is considered as a slow query and its log is output to the slow query log. Note that when the output level of log.level is "debug", all queries are recorded in the slow query log, regardless of the setting of this parameter.
  • Since v6.1.0, the threshold value of consumed time in the slow log is specified by the TiDB configuration item instance.tidb_slow_log_threshold or the system variable tidb_slow_log_threshold. slow-threshold still takes effect. But if slow-threshold and instance.tidb_slow_log_threshold are set at the same time, the latter takes effect.

record-plan-in-slow-log

  • Determines whether to record execution plans in the slow log.
  • Default value: 1
  • Since v6.1.0, whether to record execution plans in the slow log is determined by the TiDB configuration item instance.tidb_record_plan_in_slow_log or the system variable tidb_record_plan_in_slow_log. record-plan-in-slow-log still takes effect. But if record-plan-in-slow-log and instance.tidb_record_plan_in_slow_log are set at the same time, the latter takes effect.

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.

general-log-file New in v8.0.0

  • The filename of the general log.
  • Default value: ""
  • If you specify a filename, the general log is written to this specified file. If the value is blank, the general log is written to the server log of the TiDB instance. You can specify the name of the server log using filename.

timeout New in v7.1.0

  • Sets the timeout for log-writing operations in TiDB. In case of a disk failure that prevents logs from being written, this configuration item can trigger the TiDB process to panic instead of hang.
  • Default value: 0, indicating no timeout is set.
  • Unit: second
  • In some user scenarios, TiDB logs might be stored on hot-pluggable or network-attached disks, which might become permanently unavailable. In these cases, TiDB cannot recover automatically from such disaster and the log-writing operations will be permanently blocked. Although the TiDB process might seem to be running, it does not respond to any requests. This configuration item is designed to handle such situations.

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.

compression New in v8.0.0

  • The compression method for the log.
  • Default value: ""
  • Value options: "", "gzip"
  • The default value is "", which means no compression. To enable the gzip compression, set this value to "gzip". After compression is enabled, all log files are affected, such as slow-query-file and general-log-file.

Security

Configuration items related to security.

enable-sem

  • Enables the Security Enhanced Mode (SEM).
  • Default value: false
  • The status of SEM is available via the system variable tidb_enable_enhanced_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: ""

spilled-file-encryption-method

  • Determines the encryption method used for saving the spilled files to disk.
  • Default value: "plaintext", which disables encryption.
  • Optional values: "plaintext" and "aes128-ctr"

auto-tls

  • Determines whether to automatically generate the TLS certificates on startup.
  • Default value: false

tls-version

  • Set the minimum TLS version for MySQL Protocol connections.
  • Default value: "", which allows TLSv1.2 or later versions. Before TiDB v7.6.0, the default value allows TLSv1.1 or later versions.
  • Optional values: "TLSv1.2" and "TLSv1.3". Before TiDB v8.0.0, "TLSv1.0" and "TLSv1.1" are also allowed.

auth-token-jwks New in v6.4.0

  • Set the local file path of the JSON Web Key Sets (JWKS) for the tidb_auth_token authentication method.
  • Default value: ""

auth-token-refresh-interval New in v6.4.0

  • Set the JWKS refresh interval for the tidb_auth_token authentication method.
  • Default value: 1h

disconnect-on-expired-password New in v6.5.0

  • Determines whether TiDB disconnects the client connection when the password is expired.
  • Default value: true
  • Optional values: true, false
  • If you set it to true, the client connection is disconnected when the password is expired. If you set it to false, the client connection is restricted to the "sandbox mode" and the user can only execute the password reset operation.

session-token-signing-cert New in v6.4.0

  • The certificate file path, which is used by TiProxy for session migration.
  • Default value: ""
  • Empty value will cause TiProxy session migration to fail. To enable session migration, all TiDB nodes must set this to the same certificate and key. This means that you should store the same certificate and key on every TiDB node.

session-token-signing-key New in v6.4.0

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.

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.

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: 3600000
  • Unit: Millisecond
  • The transaction that holds locks longer than this time can only be committed or rolled back. The commit might not be successful.
  • For transactions executed using the "bulk" DML mode, the maximum TTL can exceed the limit of this configuration item. The maximum value is the greater value between this configuration item and 24 hours.

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 retryable 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 and v5.0.0

  • 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).
  • Starting from v7.6.0, you can use the system variable tidb_txn_entry_size_limit to dynamically modify the value of this configuration item.
  • 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.
  • The default value of max_allowed_packet (the maximum size of a packet for the MySQL protocol) is 67108864 (64 MiB). If a row is larger than max_allowed_packet, the row gets truncated.
  • The default value of txn-total-size-limit (the size limit of a single transaction in TiDB) is 100 MiB. If you increase the txn-entry-size-limit value to be over 100 MiB, you need to increase the txn-total-size-limit value accordingly.

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 1099511627776 (1 TB). 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.
  • In TiDB v6.5.0 and later versions, this configuration is no longer recommended. The memory size of a transaction will be accumulated into the memory usage of the session, and the tidb_mem_quota_query variable will take effect when the session memory threshold is exceeded. To be compatible with previous versions, this configuration works as follows when you upgrade from an earlier version to TiDB v6.5.0 or later:
    • If this configuration is not set or is set to the default value (104857600), after an upgrade, the memory size of a transaction will be accumulated into the memory usage of the session, and the tidb_mem_quota_query variable will take effect.
    • If this configuration is not defaulted (104857600), it still takes effect and its behavior on controlling the size of a single transaction remains unchanged before and after the upgrade. This means that the memory size of the transaction is not controlled by the tidb_mem_quota_query variable.
  • When TiDB executes transactions in the tidb_dml_type "bulk" mode, transaction size is not limited by the TiDB configuration item txn-total-size-limit.

tcp-keep-alive

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

tcp-no-delay

  • Determines whether to enable TCP_NODELAY at the TCP layer. After it is enabled, TiDB disables the Nagle algorithm in the TCP/IP protocol and allows sending small data packets to reduce network latency. This is suitable for latency-sensitive applications with a small transmission volume of data.
  • 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.

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 value: NO_PRIORITY
  • Value options: The default value NO_PRIORITY means that the priority for statements is not forced to change. Other options are LOW_PRIORITY, DELAYED, and HIGH_PRIORITY in ascending order.
  • Since v6.1.0, the priority for all statements is determined by the TiDB configuration item instance.tidb_force_priority or the system variable tidb_force_priority. force-priority still takes effect. But if force-priority and instance.tidb_force_priority are set at the same time, the latter takes effect.

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.

enforce-mpp

  • Determines whether to ignore the optimizer's cost estimation and to forcibly use TiFlash's MPP mode for query execution.
  • Default value: false
  • This configuration item controls the initial value of tidb_enforce_mpp. For example, when this configuration item is set to true, the default value of tidb_enforce_mpp is ON.

enable-stats-cache-mem-quota New in v6.1.0

  • Controls whether to enable the memory quota for the statistics cache.
  • Default value: true

stats-load-concurrency New in v5.4.0

  • The maximum number of columns that the TiDB synchronously loading statistics feature can process concurrently.
  • Default value: 0. Before v8.2.0, the default value is 5.
  • Currently, the valid value range is [0, 128]. The value 0 means the automatic mode, which automatically adjusts concurrency based on the configuration of the server. Before v8.2.0, the minimum value is 1.

stats-load-queue-size New in v5.4.0

  • The maximum number of column requests that the TiDB synchronously loading statistics feature can cache.
  • Default value: 1000
  • Currently, the valid value range is [1, 100000].

concurrently-init-stats New in v8.1.0 and v7.5.2

  • Controls whether to initialize statistics concurrently during TiDB startup.
  • Default value: false

lite-init-stats New in v7.1.0

  • Controls whether to use lightweight statistics initialization during TiDB startup.
  • Default value: false for versions earlier than v7.2.0, true for v7.2.0 and later versions.
  • When the value of lite-init-stats is true, statistics initialization does not load any histogram, TopN, or Count-Min Sketch of indexes or columns into memory. When the value of lite-init-stats is false, statistics initialization loads histograms, TopN, and Count-Min Sketch of indexes and primary keys into memory but does not load any histogram, TopN, or Count-Min Sketch of non-primary key columns into memory. When the optimizer needs the histogram, TopN, and Count-Min Sketch of a specific index or column, the necessary statistics are loaded into memory synchronously or asynchronously (controlled by tidb_stats_load_sync_wait).
  • Setting lite-init-stats to true speeds up statistics initialization and reduces TiDB memory usage by avoiding unnecessary statistics loading. For details, see Load statistics.

force-init-stats New in v6.5.7 and v7.1.0

  • Controls whether to wait for statistics initialization to finish before providing services during TiDB startup.
  • Default value: false for versions earlier than v7.2.0, true for v7.2.0 and later versions.
  • When the value of force-init-stats is true, TiDB needs to wait until statistics initialization is finished before providing services upon startup. Note that if there are a large number of tables and partitions and the value of lite-init-stats is false, setting force-init-stats to true might prolong the time it takes for TiDB to start providing services.
  • When the value of force-init-stats is false, TiDB can still provide services before statistics initialization is finished, but the optimizer uses pseudo statistics to make decisions, which might result in suboptimal execution plans.

opentracing

Configuration items related to opentracing.

enable

  • Enables opentracing to trace the call overhead of some TiDB components. Note that enabling opentracing causes some performance loss.
  • Default value: false

rpc-metrics

  • Enables RPC metrics.
  • Default value: false

opentracing.sampler

Configuration items related to opentracing.sampler.

type

  • Specifies the type of the opentracing sampler. The string value is case-insensitive.
  • Default value: "const"
  • Value options: "const", "probabilistic", "ratelimiting", "remote"

param

  • The parameter of the opentracing sampler.
    • For the const type, the value can be 0 or 1, which indicates whether to enable the const sampler.
    • For the probabilistic type, the parameter specifies the sampling probability, which can be a float number between 0 and 1.
    • For the ratelimiting type, the parameter specifies the number of spans sampled per second.
    • For the remote type, the parameter specifies the sampling probability, which can be a float number between 0 and 1.
  • Default value: 1.0

sampling-server-url

  • The HTTP URL of the jaeger-agent sampling server.
  • Default value: ""

max-operations

  • The maximum number of operations that the sampler can trace. If an operation is not traced, the default probabilistic sampler is used.
  • Default value: 0

sampling-refresh-interval

  • Controls the frequency of polling the jaeger-agent sampling policy.
  • Default value: 0

opentracing.reporter

Configuration items related to opentracing.reporter.

queue-size

  • The queue size with which the reporter records spans in memory.
  • Default value: 0

buffer-flush-interval

  • The interval at which the reporter flushes the spans in memory to the storage.
  • Default value: 0

log-spans

  • Determines whether to print the log for all submitted spans.
  • Default value: false

local-agent-host-port

  • The address at which the reporter sends spans to the jaeger-agent.
  • Default value: ""

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

grpc-compression-type

  • Specifies the compression type used for data transfer from TiDB nodes to TiKV nodes. The default value is "none", which means no compression. To enable the gzip compression, set this value to "gzip".
  • Default value: "none"
  • Value options: "none", "gzip"

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.

batch-policy New in v8.3.0

  • Controls the batching strategy for requests from TiDB to TiKV. When sending requests to TiKV, TiDB always encapsulates the requests in the current waiting queue into a BatchCommandsRequest and sends it to TiKV as a packet. This is the basic batching strategy. When the TiKV load throughput is high, TiDB decides whether to wait for an additional period after the basic batching based on the value of batch-policy. This additional batching allows more requests to be encapsulated in a single BatchCommandsRequest.
  • Default value: "standard"
  • Value options:
    • "basic": the behavior is consistent with versions before v8.3.0, where TiDB performs additional batching only if tikv-client.max-batch-wait-time is greater than 0 and the load of TiKV exceeds the value of tikv-client.overload-threshold.
    • "standard": TiDB dynamically batches requests based on the arrival time intervals of recent requests, suitable for high-throughput scenarios.
    • "positive": TiDB always performs additional batching, suitable for high-throughput testing scenarios to achieve optimal performance. However, in low-load scenarios, this strategy might introduce unnecessary batching wait time, potentially reducing performance.
    • "custom{...}": allows customization of batching strategy parameters. This option is intended for the internal testing of TiDB and is NOT recommended for general use.

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

copr-req-timeout New in v7.5.0

  • The timeout of a single Coprocessor request.
  • Default value: 60
  • Unit: second

enable-replica-selector-v2 New in v8.0.0

  • Whether to use the new version of the Region replica selector when sending RPC requests to TiKV.
  • Default value: true

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

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

capacity-mb

  • The total size of the cached data. When the cache space is full, old cache entries are evicted. When the value is 0.0, the Coprocessor Cache feature is disabled.
  • Default value: 1000.0
  • Unit: MB
  • Type: Float

txn-local-latches

Configuration items related to the transaction latch. These configuration items might be deprecated in the future. It is not recommended to use them.

enabled

  • 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

record-db-label

  • Determines whether to transmit the database-related QPS metrics to Prometheus.
  • Supports more metircs types than record-db-qps, for example, duration and statements.
  • Default value: false

pessimistic-txn

For pessimistic transaction usage, refer to TiDB Pessimistic Transaction Mode.

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

deadlock-history-capacity

  • The maximum number of deadlock events that can be recorded in the INFORMATION_SCHEMA.DEADLOCKS table of a single TiDB server. If this table is in full volume and an additional deadlock event occurs, the earliest record in the table will be removed to make place for the newest error.
  • Default value: 10
  • Minimum value: 0
  • Maximum value: 10000

deadlock-history-collect-retryable

pessimistic-auto-commit New in v6.0.0

  • Determines the transaction mode that the auto-commit transaction uses when the pessimistic transaction mode is globally enabled (tidb_txn_mode='pessimistic'). By default, even if the pessimistic transaction mode is globally enabled, the auto-commit transaction still uses the optimistic transaction mode. After enabling pessimistic-auto-commit (set to true), the auto-commit transaction also uses pessimistic mode, which is consistent with the other explicitly committed pessimistic transactions.
  • For scenarios with conflicts, after enabling this configuration, TiDB includes auto-commit transactions into the global lock-waiting management, which avoids deadlocks and mitigates the latency spike brought by deadlock-causing conflicts.
  • For scenarios with no conflicts, if there are many auto-commit transactions (the specific number is determined by the real scenarios. For example, the number of auto-commit transactions accounts for more than half of the total number of applications), and a single transaction operates a large data volume, enabling this configuration causes performance regression. For example, the auto-commit INSERT INTO SELECT statement.
  • When the session-level system variable tidb_dml_type is set to "bulk", the effect of this configuration in the session is equivalent to setting it to false.
  • Default value: false

constraint-check-in-place-pessimistic New in v6.4.0

isolation-read

Configuration items related to read isolation.

engines

  • Controls from which engine TiDB allows to read data.
  • Default value: ["tikv", "tiflash", "tidb"], indicating that the engine is automatically selected by the optimizer.
  • Value options: Any combinations of "tikv", "tiflash", and "tidb", for example, ["tikv", "tidb"] or ["tiflash", "tidb"]

instance

tidb_enable_collect_execution_info

  • This configuration controls whether to record the execution information of each operator in the slow query log and whether to record the usage statistics of indexes.
  • Default value: true
  • Before v6.1.0, this configuration is set by enable-collect-execution-info.

tidb_enable_slow_log

  • This configuration is used to control whether to enable the slow log feature.
  • Default value: true
  • Value options: true or false
  • Before v6.1.0, this configuration is set by enable-slow-log.

tidb_slow_log_threshold

  • Outputs the threshold value of the time consumed by the slow log.
  • Default value: 300
  • Range: [-1, 9223372036854775807]
  • Unit: Milliseconds
  • When the time consumed by a query is larger than this value, this query is considered as a slow query and its log is output to the slow query log. Note that when the output level of log.level is "debug", all queries are recorded in the slow query log, regardless of the setting of this parameter.
  • Before v6.1.0, this configuration is set by slow-threshold.

in-mem-slow-query-topn-num New in v7.3.0

  • The configuration controls the number of slowest queries that are cached in memory.
  • Default value: 30

in-mem-slow-query-recent-num New in v7.3.0

  • The configuration controls the number of recently used slow queries that are cached in memory.
  • Default value: 500

tidb_expensive_query_time_threshold

  • This configuration is used to set the threshold value that determines whether to print expensive query logs. The difference between expensive query logs and slow query logs is:
    • Slow logs are printed after the statement is executed.
    • Expensive query logs print the statements that are being executed, with execution time exceeding the threshold value, and their related information.
  • Default value: 60
  • Range: [10, 2147483647]
  • Unit: Seconds
  • Before v5.4.0, this configuration is set by expensive-threshold.

tidb_record_plan_in_slow_log

  • This configuration is used to control whether to include the execution plan of slow queries in the slow log.
  • Default value: 1
  • Value options: 1 (enabled, default) or 0 (disabled).
  • The value of this configuration will initialize the value of system variable tidb_record_plan_in_slow_log
  • Before v6.1.0, this configuration is set by record-plan-in-slow-log.

tidb_force_priority

  • This configuration is used to change the default priority for statements executed on a TiDB server.
  • Default value: NO_PRIORITY
  • The default value NO_PRIORITY means that the priority for statements is not forced to change. Other options are LOW_PRIORITY, DELAYED, and HIGH_PRIORITY in ascending order.
  • Before v6.1.0, this configuration is set by force-priority.

max_connections

  • The maximum number of connections permitted for a single TiDB instance. It can be used for resources control.
  • Default value: 0
  • Range: [0, 100000]
  • The default value 0 means no limit. When the value of this variable is larger than 0, and the number of connections reaches the value, the TiDB server will reject new connections from clients.
  • The value of this configuration will initialize the value of system variable max_connections
  • Before v6.2.0, this configuration is set by max-server-connections.

tidb_enable_ddl

  • This configuration controls whether the corresponding TiDB instance can become a DDL owner or not.
  • Default value: true
  • Possible values: OFF, ON
  • The value of this configuration will initialize the value of the system variable tidb_enable_ddl
  • Before v6.3.0, this configuration is set by run-ddl.

tidb_stmt_summary_enable_persistent New in v6.6.0

tidb_stmt_summary_filename New in v6.6.0

  • When statements summary persistence is enabled, this configuration specifies the file to which persistent data is written.
  • Default value: tidb-statements.log

tidb_stmt_summary_file_max_days New in v6.6.0

  • When statements summary persistence is enabled, this configuration specifies the maximum number of days to keep persistent data files.
  • Default value: 3
  • Unit: day
  • You can adjust the value based on the data retention requirements and disk space usage.

tidb_stmt_summary_file_max_size New in v6.6.0

  • When statements summary persistence is enabled, this configuration specifies the maximum size of a persistent data file.
  • Default value: 64
  • Unit: MiB
  • You can adjust the value based on the data retention requirements and disk space usage.

tidb_stmt_summary_file_max_backups New in v6.6.0

  • When statements summary persistence is enabled, this configuration specifies the maximum number of data files that can be persisted. 0 means no limit on the number of files.
  • Default value: 0
  • You can adjust the value based on the data retention requirements and disk space usage.

proxy-protocol

Configuration items related to the PROXY protocol.

networks

  • The list of proxy server's IP addresses allowed to connect to TiDB using the PROXY protocol
  • Default value: ""
  • In general cases, when you access TiDB behind a reverse proxy, TiDB takes the IP address of the reverse proxy server as the IP address of the client. By enabling the PROXY protocol, reverse proxies that support this protocol, such as HAProxy, can pass the real client IP address to TiDB.
  • After configuring this parameter, TiDB allows the configured source IP address to connect to TiDB using the PROXY protocol; if a protocol other than PROXY is used, this connection will be denied. If this parameter is left empty, no IP address can connect to TiDB using the PROXY protocol. The value can be an IP address (192.168.1.50) or CIDR (192.168.1.0/24) with , as the separator. * means any IP addresses.

fallbackable New in v6.5.1

  • Controls whether to enable the PROXY protocol fallback mode. If this configuration item is set to true, TiDB can accept clients that belong to proxy-protocol.networks to connect to TiDB without using the PROXY protocol specification or without sending the PROXY protocol header. By default, TiDB only accepts client connections that belong to proxy-protocol.networks and send a PROXY protocol header.
  • Default value: false

experimental

The experimental section, introduced in v3.1.0, describes the configurations related to the experimental features of TiDB.

allow-expression-index New in v4.0.0

  • Controls whether an expression index can be created. Since TiDB v5.2.0, if the function in an expression is safe, you can create an expression index directly based on this function without enabling this configuration. If you want to create an expression index based on other functions, you can enable this configuration, but correctness issues might exist. By querying the tidb_allow_function_for_expression_index variable, you can get the functions that are safe to be directly used for creating an expression.
  • Default value: false

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