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TDSQL-C for MySQL
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    System Variables

    Last updated: 2024-12-17 16:51:55
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      This document provides a detailed list of variables that can be specified using SET_VAR in SQL HINT.

      Runtime Filter-related

      System Variable
      Meaning
      Parameter Type
      Default Value
      Value Range
      Scope
      Supporting SET_VAR Hint
      libra_enable_runtime_filter
      Whether to enable Runtime Filter.
      BOOL
      ON
      ON: Enable Runtime Filter.
      OFF: Disable Runtime Filter.
      Global & Session
      Yes
      libra_runtime_filter_type
      Set the Runtime Filter type that can be assigned.
      VARCHAR
      MIN_MAX, BLOOM_FILTER, IN_FILTER
      BLOOM_FILTER: Builds a Bloom Filter for the JOIN KEY of the JOIN BUILD side to filter the Probe side data.
      MIN_MAX: Builds maximum and minimum values for the JOIN KEY of the JOIN BUILD side to filter the Probe side data.
      IN: Builds a value list for the JOIN KEY of the JOIN BUILD side to filter the Probe side data.
      Empty string: Indicates disabling the Runtime Filter feature.
      Global & Session
      Yes
      libra_enable_cost_based_runtime_filter
      Enable/Disable cost-based Runtime Filter.
      BOOL
      ON
      ON: Enable cost-based Runtime Filter assignment.
      OFF: Disable cost-based Runtime Filter assignment.
      Global & Session
      Yes
      libra_max_in_runtime_filter_ndv
      The maximum value of NDV (Number of Distinct Values) on the BUILD side when an IN type Runtime Filter is generated in cost-based Runtime Filters.
      INT
      1024
      0-MaxValue
      Global & Session
      Yes
      runtime_filter_wait_time_ms
      The maximum time to initially wait for RF Ready on the RF USE side. 0 indicates waiting indefinitely until timeout or interrupting query execution.
      INT
      100
      [0, MaxValue)
      Global & Session
      Yes

      Late Materialization-related

      System Variable
      Meaning
      Parameter Type
      Default Value
      Value Range
      Scope
      Supporting SET_VAR Hint
      libra_enable_late_materialization
      Whether to enable late materialization.
      BOOL
      OFF
      ON: Enable late materialization.
      OFF: Disable late materialization.
      Global & Session
      Yes

      Parallelism & Concurrency-related

      System Variable
      Meaning
      Parameter Type
      Default Value
      Value Range
      Scope
      Supporting SET_VAR Hint
      max_threads
      Parallelism during query execution.
      INT
      Number of the CPU cores of the node
      0-MaxValue (recommended not to exceed twice the number of CPU cores)
      Global & Session
      Yes

      Execution Engine-related

      System Variable
      Meaning
      Parameter Type
      Default Value
      Value Range
      Scope
      Supporting SET_VAR Hint
      
      max_bytes_before_external_agg_uniq_exact
      The limit of the hashset when the uniqExactDisk calculation function is used for CountDistinct. If the hashset exceeds this limit, switching to external memory will be started. The default is 0, indicating no external memory computing.
      INT
      0
      [0, MaxValue)
      Global & Session
      Yes
      one_bucket_max_temp_file_size
      The maximum size of each file written to the bucket when the uniqExactDisk calculation function is used for CountDistinct. If this value is exceeded, switching to a new file for writing is required.
      INT
      0
      [0, MaxValue)
      Global & Session
      Yes
      count_distinct_implementation
      The name of the calculation function used for CountDistinct. The default is uniqExactDisk.
      VARCHAR
      uniqExactDisk
      uniqExactDisk: Indicates a precise CountDistinct calculation method with the writing feature.
      uniq: Indicates an approximate CountDistinct calculation method.
      uniqExact: Indicates a precise CountDistinct calculation method with the pure memory.
      -
      Yes
      join_build_concurrency
      Specifies the parallelism used for Join Build. The default is 0, indicating that the Default or specified MaxThreads is used.
      INT
      0
      [0, MaxValue)
      Global & Session
      Yes
      enable_local_tunnel
      Supports communication optimization for local Sender and Receiver.
      BOOL
      ON
      ON: Enable communication optimization for Local Channel.
      OFF: Disable communication optimization for Local Channel.
      Global & Session
      Yes
      mpp_max_packet_size
      The maximum size of a packet sent by the Sender. 0 indicates no limit.
      INT
      0
      [0, MaxValue)
      Global & Session
      Yes
      tunnel_buffer_size
      The BUFFER quantity of the send buffer queue on the Sender side. The default is 1.
      INT
      1
      [0, MaxValue)
      Global & Session
      Yes
      pipeline_executor_use_thread_manager
      Use a dynamic thread pool model for the Pipeline model.
      BOOL
      OFF
      ON: Enable using a dynamic thread pool for the Pipeline model.
      OFF: Disable using a dynamic thread pool for the Pipeline model.
      Global & Session
      Yes
      enable_order_by_push_down
      Enable/Disable the ORDER BY push-down feature.
      BOOL
      ON
      ON: Enable the ORDER BY push-down feature.
      OFF: Disable the ORDER BY push-down feature.
      Global & Session
      Yes
      max_block_size
      Set the number of rows in the data block passed in the Pipeline execution engine.
      INT
      65409
      [1, MaxValue)
      Global & Session
      Yes
      shuffle_after_join
      Set whether to shuffle data to multiple Pipelines after join.
      BOOL
      ON
      ON: Enable the shuffle feature.
      OFF: Disable the shuffle feature.
      Global & Session
      Yes
      disable_mysql_compatible
      Whether to add Cast in expression calculation for MySQL compatibility.
      BOOL
      TRUE
      TRUE: Not compatible with MySQL.
      FALSE: Compatible with MySQL.
      Global & Session
      Yes
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