Kbase P74425: Define the _userio-dbaccess, _userio-dbread, and _userio-dbwrite counters.
| Autor |
Progress Software Corporation - Progress |
| Acesso |
Público |
| Publicação |
05/11/2009 |
|
Status: Verified
GOAL:
What do the _userio-dbaccess, _userio-dbread, and _userio-dbwrite counters mean?
FIX:
The _userio-dbaccess counter tells you the number of times that particular user (really that database connection) accessed a database cache buffer in memory, either to retrieve data from it (for example, a record fetch or an index lookup) or to update it (for example, to do a record create, delete or update, index insert, etc). The purpose of the buffer cache is to minimize the need for disk I/O operations, which are much more time consuming than copying data already in memory.
The _userio-dbread counter tells you the number of times that particular user (database connection) had to read a block from disk because it was not already present in the buffer cache. In most cases, after a database block has been read into the buffer cache, it is accessed multiple times without requiring additional disk transfers, possibly by many different users (database connections).
The _userio-dbwrite counter tells you the number of times that user (database connection) wrote a database block to disk. In most cases, the user (database connection) that updates a database buffer is not the same one that later writes it to disk.It is a good thing for the _userio-dbread and _userio-dbwrite counters to be zero (or small numbers). That means that the data the user (database connection) is using is present in memory and thus disk transfer are being avoided. Avoiding disk transfers increases performance.Using NO-LOCK or not using it has no bearing on the beaviour of the database buffer cache manager.