Global SysCache Parameters
enable_global_syscache
Parameter description: Specifies whether to enable the global system cache function. This parameter is a POSTMASTER parameter. Set it based on instructions provided in Table 1.
Value range: Boolean
- on indicates that the global system cache function is enabled.
- off indicates that the global system cache function is disabled.
Default value: off
You are advised to use this parameter together with the thread pool parameter. After this parameter is enabled, you are advised to set wal_level of the standby nnode to hot_standby or higher if you need to access the standby node.
global_syscache_threshold
Parameter description: Specifies the maximum memory usage of the global system cache. If this parameter is set to a small value, memory is frequently evicted, and a large number of memory fragments cannot be recycled. As a result, memory control fails. This parameter takes effect only when the enable_global_syscache parameter is enabled.
This parameter is a SIGHUP parameter. Set it based on instructions provided in Table 1.
Value range: an integer ranging from 16384 to 1073741824. The unit is KB.
Default value: 163840
Recommended calculation formula: The smaller value of the number of hot databases and the number of threads x Memory size allocated to each database. That is, global_syscache_threshold = min(count(hot dbs),count(threads)) * memofdb.
Note:
- hot dbs: number of hot databases, that is, databases that are frequently accessed.
- threads: number of threads. In thread pool mode, the value is the sum of the number of threads in the thread pool and the number of backend threads. In non-thread pool mode, the value does not need to be calculated and the number of hot databases is used.
- memofdb indicates the average memory allocated to each database. The background noise memory of each database is 2 MB. Each time a table or index is added, 11 KB memory is added.