Help Center/ GaussDB/ Feature Guide(Centralized_8.x)/ Storage Engine/ Data Lifecycle Management: OLTP Table Compression/ Setting the Maintenance Window Parameters
Updated on 2024-06-07 GMT+08:00
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Setting the Maintenance Window Parameters

  • RETENTION_TIME: duration for storing evaluation and compression records, in days. The default value is 30. You can adjust the value based on your storage capacity.
  • EXECUTION_INTERVAL: execution frequency of an evaluation task, in minutes. The default value is 15. You can adjust the value based on the service and resource usage during the maintenance window. This parameter and ABS_JOBLIMIT affect each other. A single thread can generate a maximum of WIND_DURATION/EXECUTION_INTERVAL x JOB_SIZELIMIT I/Os per day.
  • JOB_SIZELIMIT: maximum number of bytes that can be processed by a single compression job. The unit is MB. The default value is 1024. The compression processing rate is about 100 MB/s. When the I/O limit of each compression job is 1 GB, the compression job can be completed within 10 seconds. You can adjust the value based on the service off-peak hours and the amount of data to be compressed.
  • ABS_JOBLIMIT: maximum number of compression jobs that can be generated in an evaluation. You can adjust the value based on the number of partitions and tables in the configured policy. It is recommended that the value be less than or equal to 10. You can run the select count(*) from gs_adm_ilmobjects where enabled = true command to query the value.
  • POLICY_TIME: specifies whether the time unit for determining cold rows is day or second. The time unit second is used only for testing. The value can be ILM_POLICY_IN_SECONDS or ILM_POLICY_IN_DAYS (default value).
  • WIND_DURATION: maintenance window duration, in minutes. The default value is 240 minutes (4 hours). By default, the maintenance window lasts 240 minutes from 22:00 (Beijing time). You can adjust the maintenance window based on service off-peak hours.
  • BLOCK_LIMITS: upper limit of the instance-level row-store compression rate. The default value is 40. The value ranges from 0 to 10000, in block/ms, indicating the maximum number of blocks that can be compressed per millisecond. 0 indicates that the rate is not limited. The maximum rate is calculated as follows: BLOCK_LIMITS x 1000 x BLOCKSIZE. For example, if the default value is 40, the maximum rate is 320,000 KB/s (40 x 1000 x 8 KB).
Example: 
EXECUTION_INTERVAL: 15
JOB_SIZELIMIT: 10240
WIND_DURATION: 240
BLOCK_LIMITS: 0

In this configuration, for a single table partition or sub-partition, a total of 160 GB (240/15 x 10240 MB) data can be evaluated and compressed during a maintenance window. The compression processing rate is 100 MB/s, but the actual compression takes only 27 minutes (160 GB/(100 MB/s) = 27 minutes). Services are not affected in other periods. You can adjust the parameters based on the available compression period during off-peak hours.