This section describes parameters related to statement disk space control, which are used to limit the disk space usage of statements.
sql_use_spacelimit
Parameter description: Specifies the space size for files to be spilled to disks when a single SQL statement is executed on a single DN. The managed space includes the space occupied by ordinary tables, temporary tables, and intermediate result sets to be flushed to disks. System administrators are also restricted by this parameter.
Type: USERSET
Value range: an integer ranging from -1 to INT_MAX. The unit is KB. –1 indicates no limit.
Default value: –1
Setting suggestion: You are advised to set sql_use_spacelimit to 10% of the total disk space where DNs reside. If two DNs exist on a single disk, set sql_use_spacelimit to 5% of the total disk space.
For example, if sql_use_spacelimit is set to 100 in the statement and the amount data spilled to disks on a single DN exceeds 100 KB, DWS stops the query and displays a message of threshold exceeding.
1 2 | insert into user1.t1 select * from user2.t1; ERROR: The space used on DN (104 kB) has exceeded the sql use space limit (100 kB). |
Handling suggestion:
- Optimize the statement to reduce the data spilled to disks.
- If the disk space is sufficient, increase the value of this parameter.
temp_file_limit
Parameter description: Specifies the total space for files spilled to disks in a single thread. For example, temporary files used by sorting and hash tables or cursors are controlled by this parameter.
This is a session-level setting.
Type: SUSET
Value range: an integer ranging from -1 to INT_MAX. The unit is KB. –1 indicates no limit.
Default value: –1
This parameter does not apply to disk space occupied by temporary tablespaces used for executing SQL queries.
bi_page_reuse_factor
Parameter description: Specifies the percentage of idle space of old pages that can be reused when page replication is used for data synchronization between primary and standby DNs in the scenario where data is inserted into row-store tables in batches.
Type: USERSET
Value range: an integer ranging from 0 to 100. The value is a percentage. Value 0 indicates that the old pages are not reused and new pages are requested.
Default value: 70
- In an upgrade, the default value of this parameter is the same as that in the cluster before the upgrade. In a newly installed 8.1.1.500 cluster, the default value of this parameter is 0.
- You are not advised to set this parameter to a value less than 50 (except 0). If the idle space of the reused page is small, too much old page data will be transmitted between the primary and standby DNs. As a result, the batch insertion performance deteriorates.
- You are not advised to set this parameter to a value greater than 90. If this parameter is set to a value greater than 90, idle pages will be frequently queried, but old pages cannot be reused.