Asynchronous I/O Operations

enable_adio_debug

Parameter description: Specifies whether O&M personnel are allowed to generate some ADIO logs to locate ADIO issues. This parameter is used only by developers. Common users are advised not to use it.

This parameter is a SUSET parameter. Set it based on instructions provided in Table 1 GUC parameters.

Value range: Boolean

• on or true indicates that generation of ADIO logs is allowed.
• off or false indicates that generation of ADIO logs is disallowed.

Default value: off

NOTE: This parameter cannot be enabled on in the current version. Even if it is manually enabled, the system automatically disables it.

enable_adio_function

Parameter description: Specifies whether to enable the ADIO function.

This parameter is an INTERNAL parameter, which is fixed. The user cannot modify it but review it only.

NOTE: The current version does not support the asynchronous I/O function. This function is disabled by default. Do not modify the setting.

Value range: Boolean

• on or true indicates that the function is enabled.
• off or false indicates that the function is disabled.

Default value: off

enable_fast_allocate

Parameter description: Specifies whether the quick disk space allocation is enabled.

This parameter is a SUSET parameter. Set it based on instructions provided in Table 1 GUC parameters. This function can be enabled only in the XFS file system.

Value range: Boolean

• on or true indicates that the function is enabled.
• off or false indicates that the function is disabled.

Default value: off

prefetch_quantity

Parameter description: Specifies the amount of the I/O that the row-store prefetches using the ADIO.

This parameter is a USERSET parameter. Set it based on instructions provided in Table 1 GUC parameters.

Value range: an integer ranging from 128 to 131072. The unit is 8 kB.

Default value: 32MB (4096 x 8 kB)

backwrite_quantity

Parameter description: Specifies the amount of I/O that the row-store writes using the ADIO.

This parameter is a USERSET parameter. Set it based on instructions provided in Table 1 GUC parameters.

Value range: an integer ranging from 128 to 131072. The unit is 8 kB.

Default value: 8MB (1024 x 8 kB)

cstore_prefetch_quantity

Parameter description: Specifies the amount of I/O that the column-store prefetches using the ADIO.

This parameter is a USERSET parameter. Set it based on instructions provided in Table 1 GUC parameters.

Value range: an integer ranging from 1024 to 1048576. The unit is kB.

Default value: 32MB

cstore_backwrite_quantity

Parameter description: Specifies the amount of I/O that the column-store writes using the ADIO.

This parameter is a USERSET parameter. Set it based on instructions provided in Table 1 GUC parameters.

Value range: an integer ranging from 1024 to 1048576. The unit is kB.

Default value: 8MB

cstore_backwrite_max_threshold

Parameter description: Specifies the maximum amount of buffer I/O that the column-store writes in the database using the ADIO.

This parameter is a USERSET parameter. Set it based on instructions provided in Table 1 GUC parameters.

Value range: an integer ranging from 4096 to INT_MAX/2. The unit is kB.

Default value: 2GB

fast_extend_file_size

Parameter description: Specifies the disk size that the row-store pre-scales using the ADIO.

This parameter is a SUSET parameter. Set it based on instructions provided in Table 1 GUC parameters.

Value range: an integer ranging from 1024 to 1048576. The unit is kB.

Default value: 8MB

effective_io_concurrency

Parameter description: Specifies the number of requests that can be simultaneously processed by a disk subsystem. For the RAID array, the parameter value must be the number of disk drive spindles in the array.

This parameter is a USERSET parameter. Set it based on instructions provided in Table 1 GUC parameters.

Value range: an integer ranging from 0 to 1000

Default value: 1