F.3 VCI Memory Requirements

This section describes the formula for estimating VCI memory requirements.

Use the following formula to obtain a rough estimate of memory requirements:

memUsedByVci = memForData + memForEachProcess

Memory required to store data in memory

Secure the space estimated using the formula below on the stable buffer (part of shared_buffers).

memForData = (numOfRowsInTables) x (numOfBytesPerRow) + (wosSize)

Number of bytes per row

numOfBytesPerRow
 = (19 + (numOfColsInCreateIndexStatement) / 8 + (numOfBytesPerSingleColValue)) x 1.1

Note: Round up the result to the nearest integer.

WOS size

wosSize = (numOfWosRows) / 185 x 8096

One row is added to the number of WOS rows for each INSERT and DELETE, and two rows are added for UPDATE. On the other hand, the number decreases to 520,000 rows or less during conversion to ROS performed by the ROS control daemon.

Memory required for each process

memForEachProcess
 = memUsedPerScanning
 + memUsedForVciMaintenace
 + memUsedByCreateIndexStatement

Memory used per scanning

Parallel scan
```
memUsedPerScanning 
 = vci.shared_work_mem + (numOfParallelWorkers + 1) x vci.maintenance_work_mem
```
Note: The number of parallel workers used by VCI simultaneously in the entire instance is equal to or less than vci.max_parallel_degree.

Non-parallel scan

memUsedPerScanning = vci.max_local_ros + vci.maintenance_work_mem

Note

vci.shared_work_mem, and vci.max_local_ros are used to create local ROS. If local ROS exceeds these sizes, execute a query without using VCI according to the conventional plan.
vci.maintenance_work_mem specifies the memory size to be secured dynamically. If it exceeds the specified value, a disk temporary file is used for operation.

Memory used for VCI maintenance

memUsedForVciMaintenace = vci.maintenance_work_mem x vci.control_max_workers

Memory used by CREATE INDEX

memUsedByCreateIndexStatement = vci.maintenance_work_mem

Note

vci.maintenance_work_mem specifies the memory to be secured dynamically. If it exceeds the specified value, a disk temporary file is used for operation.