6.3.7.2 Monitoring Smart I/O Using Database Statistics and Wait Events

The following table describes various database statistics that are useful for monitoring smart I/O operations. The statistics are available in various dynamic performance views, including V$SYSSTAT, and may be displayed in the Global Activity Statistics or Instance Activity Statistics section of an AWR report.

Statistic	Description
cell IO uncompressed bytes	The total size of uncompressed data that is processed on the cell. For operations on segments compressed using Exadata Hybrid Columnar Compression, this statistic is the size of the data after decompression.
cell num bytes in block IO during predicate offload	The number of bytes that were not offloaded because the client was in block I/O mode.
cell num bytes in filter passthru due to low mem	The number of bytes that were not offloaded and sent back to the database for processing due to a low memory on the cell.
cell num bytes in filter passthru due to subheap size limit exc	The number of bytes that were not offloaded and sent back to the database for processing due to a memory limit on the cell.
cell num bytes in passthru due to quarantine	The number of bytes that were not offloaded and sent back to the database for processing due to a quarantine on the cell.
cell num bytes in passthru during predicate offload	The number of bytes that were not offloaded and sent back to the database for processing.
cell num smart IO sessions in rdbms block IO due to big payload	The number of sessions in block I/O mode (not offloaded) due to excessively large metadata.
cell num smart IO sessions in rdbms block IO due to no cell mem	The number of sessions in block I/O mode (not offloaded) due to memory shortage on the storage servers.
cell num smart IO sessions in rdbms block IO due to online encr	The number of sessions in block I/O mode (not offloaded) due to an ongoing online encryption operation.
cell num smart IO sessions in rdbms block IO due to open fail	The number of sessions in block I/O mode (not offloaded) due to a failure in opening a connection to a cell.
cell num smart IO sessions in rdbms block IO due to user	The number of sessions in block I/O mode (not offloaded) due to a user setting.
cell num smart IO sessions using passthru mode due to cellsrv	The number of sessions in passthru mode (not offloaded) due to an issue with CELLSRV.
cell num smart IO sessions using passthru mode due to timezone	The number of sessions in passthru mode (not offloaded) due to an ongoing database timezone upgrade operation.
cell num smart IO sessions using passthru mode due to user	The number of sessions in passthru mode (not offloaded) due to a user setting.
cell physical IO bytes added to storage index	The number of bytes added to the storage index during a Smart Scan. This is an indication that the storage index is being built.
cell physical IO bytes eligible for predicate offload	The number of bytes on-disk eligible for predicate offload.
cell physical IO bytes eligible for smart IOs	The number of actual bytes eligible for predicate offload. For example, when using columnar cache, this is the size of columnar cache instead of the on-disk size.
cell physical IO bytes processed for IM capacity	The number of bytes read from the columnar cache in memcompress for capacity format.
cell physical IO bytes processed for IM query	The number of bytes read from the columnar cache in memcompress for query format.
cell physical IO bytes processed for no memcompress	The number of bytes read from the columnar cache in no memcompress format.
cell physical IO bytes processed for XrCC	The number of bytes read from the columnar cache on Exadata RDMA Memory (XRMEM).
cell physical IO bytes saved by columnar cache	The number of bytes saved by columnar cache; that is, the number of bytes of reading that was avoided.
cell physical IO bytes saved by storage index	The number of bytes saved by storage index.
cell physical IO bytes saved during optimized file creation	The number of I/O bytes saved by the database host by offloading the file creation operation to the cells. This statistic shows the benefit of optimized file creation operations.
cell physical IO bytes saved during optimized RMAN restore	The number of I/O bytes saved by the database host by offloading the RMAN file restore operation to the cells. This statistic shows the benefit of optimized RMAN file restore operations.
cell physical IO bytes sent directly to DB node to balance CPU usage	The number of I/O bytes sent back to the database server for processing due to high storage server CPU usage.
cell physical IO interconnect bytes	The number of I/O bytes exchanged over the interconnect between the database host and the cells.
cell physical IO interconnect bytes returned by smart scan	The number of I/O bytes that are returned by the cell for Smart Scan operations. It does not include bytes for other database I/O.

The following table describes database wait events that are useful for monitoring smart I/O operations. The wait events are visible in various dynamic performance views, including V$SESSION, V$SYSTEM_EVENT and V$SESSION_EVENT, and may be displayed in the Wait Event sections of the AWR report.

Wait Event	Description
cell external table smart scan	This wait event appears when the database is waiting for an external table scan on a cell. The cell hash number in the P1 column in V$SESSION can help to identify a slow cell compared to the rest of the cells.
cell smart file creation	This wait event appears when the database is waiting for the completion of a file creation on a cell. The cell hash number in the P1 column in V$SESSION can help to identify a slow cell compared to the rest of the cells.
cell smart incremental backup	This wait event appears when the database is waiting for the completion of an incremental backup on a cell. The cell hash number in the P1 column in V$SESSION can help to identify a slow cell compared to the rest of the cells.
cell smart index scan	This wait event appears when the database is waiting for an index fast full scan. The cell hash number in the P1 column in V$SESSION can help to identify a slow cell when compared to the rest of the cells.
cell smart index scan: db timezone upgrade	The wait event appears when the cells are unable to offload because a database timezone upgrade is in progress.
cell smart index scan: disabled by user	The wait event appears when the cells are unable to offload due to a user setting.
cell smart index scan: pass through	The wait event appears when the cells are unable to offload the Smart Scan.
cell smart index scan request	This is a placeholder wait event associated with cell smart index scan, which is only visible during the wait period. After the wait event ends, the placeholder is typically converted to cell smart index scan. However, to better describe the wait outcome, the placeholder may be converted to cell smart index scan: db timezone upgrade, cell smart index scan: disabled by user, or cell smart index scan: pass through.
cell smart restore from backup	This wait event appears when the database is waiting for the completion of a file initialization for restore from backup on a cell. The cell hash number in the P1 column in V$SESSION can help to identify a slow cell when compared to the rest of the cells.
cell smart table scan	This wait event appears when the database is waiting for smart scans to complete on a cell. The cell hash number in the P1 column in V$SESSION can help to identify a slow cell when compared to the rest of the cells.
cell smart table scan: db timezone upgrade	The wait event appears when the cells are unable to offload because a database timezone upgrade is in progress.
cell smart table scan: disabled by user	The wait event appears when the cells are unable to offload due to a user setting.
cell smart table scan: pass through	The wait event appears when the cells are unable to offload the Smart Scan.
cell smart table scan request	This is a placeholder wait event associated with cell smart table scan, which is only visible during the wait period. After the wait event ends, the placeholder is typically converted to cell smart table scan. However, to better describe the wait outcome, the placeholder may be converted to cell smart table scan: db timezone upgrade, cell smart table scan: disabled by user, or cell smart table scan: pass through.

The availability of a specific statistic or wait event is subject to the version of Oracle Database being used.