Multi-Level Cache Management Parameters

enable_nvm

Parameter Description: Whether to enable the multi-level cache management feature. Once enabled, it cannot be modified.

This parameter is of the POSTMASTER type. Please refer to the corresponding setting method in the GUC parameter configuration.

Value Range: Boolean, on/off. on indicates that the multi-level cache management feature is enabled in the current installation, off indicates that it is not enabled.

Default Value: off

Note:

• When enabled, the original cache pool is divided into a Dram Buffer Pool and an Nvm Buffer Pool. The migration of pages between cache levels is controlled by access frequency, allowing hot data to reside in memory, warm data in NVM, and cold data on disk.
• The parameters nvm_buffers, nvm_file_path, bypass_nvm, and bypass_dram will only take effect when enable_nvm is set to on.

nvm_buffers

Parameter Description: The size of the Nvm Buffer Pool.

This parameter is of the POSTMASTER type. Please refer to the corresponding setting method in the GUC parameter configuration.

Value Range: Integer, 0~2147483647

Default Value: 0

nvm_file_path

Parameter Description: The path for the NVM file.

This parameter is of the POSTMASTER type. Please refer to the corresponding setting method in the GUC parameter configuration.

Value Range: String, NVM file path

Note:

The NVM medium (e.g., SCM) is exposed to applications in App Direct mode through a file system interface. MogDB achieves byte-addressing of the NVM medium by mmap-ing the NVM file, effectively using it as a cache for MogDB.

bypass_nvm

Parameter Description: The probability of bypassing the NVM cache pool and directly loading pages into the DRAM cache pool when there is a cache miss.

This parameter is of the POSTMASTER type. Please refer to the corresponding setting method in the GUC parameter configuration.

Value Range: Float, 0.0~1.0

Default Value: 0.5

bypass_dram

Parameter Description: The probability of migrating pages from the NVM cache pool to the DRAM cache pool when there is a cache hit.

This parameter is of the POSTMASTER type. Please refer to the corresponding setting method in the GUC parameter configuration.

Value Range: Float, 0.0~1.0

Default Value: 0.01

Note:

• For example, with the default value of 0.01, when a page hits in the NVM cache pool, there is a 1% probability that it will be migrated to the DRAM cache pool.