Buffer activity (_ActBuffer)

The _ActBuffer VST displays the activity of the database buffer cache, such as the number of logical reads and writes, OS reads and writes, checkpoints, deferred writes, LRU skips and writes, and APW enqueues.1

Note: The _ActBuffer table, which contains buffer activity data, holds three records: the first record contains the totals of both the Alternate and primary buffer pools; the second record contains data on the primary buffer pool; the third record contains data on the Alternate Buffer Pool
Field name Data type Description
_Buffer-Active INT64 Number of buffers active in each buffer pool
_Buffer-APWEnq INT64 Number of modified buffers placed on the APW queue for writing.
_Buffer-Area INT64 Area number
_Buffer-BlockMap INT64 Block allocation bit map block (Contains a bit map of block allocation within the object. It is allocated, but is currently not used. Accesses can show up in the buffer pool.)
_Buffer-Chkpts INT64 Number of checkpoint operations.
_Buffer-ClusterMap INT64 Cluster bit Map Blocks (Contains a bit map of cluster allocation within the area. It is allocated, but is currently not used. Accesses can show up in the buffer pool.)
_Buffer-Control INT64 Number of control blocks.
_Buffer-Deferred INT64 Total number of changes to blocks that occurred before the blocks were written. Each deferred write is potentially an I/O operation saved.
_Buffer-Free INT64 Number of free buffers
_Buffer-Flushed INT64 Number of blocks that were not written during the checkpoint and that had to be written all at once at the end of the checkpoint.
_Buffer-Index INT64 Number of index blocks buffered
_Buffer-LogicRds INT64 Number of client requests for database block read operations.
_Buffer-LogicWrts INT64 Number of client requests for database block write operations.
_Buffer-LRUEnabled LOGICAL True when all the buffers in the Alternate Buffer Pool (-B2) are consumed and an LRU replacement algorithm is utilized for buffer eviction.
_Buffer-LRUSkips INT64 Number of times a buffer on the LRU chain was skipped because it was locked or modified.
_Buffer-LRUwrts INT64 Number of blocks written to free a buffer for a read operation.
_Buffer-Marked INT64 Number of blocks scheduled to be written before the end of a checkpoint.
_Buffer-Master INT64 Buffer identifier. Valid values are:
  • 0 — Primary buffer pool
  • 1 — Secondary buffer pool
_Buffer-Object INT64 Number of object blocks
_Buffer-ObjClist INT64 Object Cluster List Blocks (contains the list of clusters owned by a particular object)
_Buffer-ObjList INT64 Number of object list blocks
_Buffer-OSRds INT64 Number of database blocks read from disk
_Buffer-OSWrts INT64 Number of database block writes to disk
_Buffer-RM INT64 Number of record blocks buffered
_Buffer-Seq INT64 Number of sequence blocks
_Buffer-Trans INT64 Number of transactions committed
_Buffer-Uptime INTEGER Number of seconds the database was opened
1 Activity and status of ABL temp-tables is available in this virtual system table. The statistics gathered allow you to monitor the operation and performance of deployed client temp-tables. Specify the range of temp-tables to track with the -ttbasetable and -tttablerangesize startup parameters. Specify temp table indexes with -ttbaseindex and -ttindexrangesize startup parameters. For more information monitoring and debugging temp tables with VSTs, see Troubleshoot ABL Applications.