tencent cloud

All product documents
TDSQL-C for MySQL
DocumentationTDSQL-C for MySQLOperation GuideRead-Only Analysis EnginePerformance OptimizationSystem Variables
System Variables
Download PDF
Last updated: 2024-12-17 16:51:55
System Variables
Last updated: 2024-12-17 16:51:55
Download PDF
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
Was this page helpful?
You can also Contact Sales or Submit a Ticket for help.
Yes
No

Feedback

Contact Us

Contact our sales team or business advisors to help your business.

Contact Us
Technical Support

Open a ticket if you're looking for further assistance. Our Ticket is 7x24 avaliable.

Submit a Ticket
7x24 Phone Support
Hong Kong, China
+852 800 906 020 (Toll Free)
United States
+1 844 606 0804 (Toll Free)
United Kingdom
+44 808 196 4551 (Toll Free)
Canada
+1 888 605 7930 (Toll Free)
Australia
+61 1300 986 386 (Toll Free)
EdgeOne hotline
+852 300 80699
More local hotlines coming soon