HP ProLiant 3000 DSS Sizing and Tuning of Oracle8 for Windows NT on Compaq Ser - Page 6

Page 4 DSS Sizing and Tuning of Oracle8 for Windows NT on Compaq Servers Figure 2: Control Panel/Services - Oracle8 Server instances NOTE: Performance Monitor does separate the instances on the chart, log, and report. However the instances are all identified as "oracle80", making it very difficult to monitor multiple instances using Performance Monitor. An Oracle instance consists of the System Global Area (SGA) and the Oracle service/ background/ shadow threads. Via an Oracle instance, an Oracle database can be created and accessed. The SGA is a sharable memory construct that contains the following: • Database Buffers • Shared Pool • Redo Log Buffers Contains most recently used database blocks Contains shared SQL areas and data dictionary cache Logs changes made to the database Figure 3: The Oracle8 Server background threads consist of the following: Thread Abbreviation Description Process Monitor PMON Responsible for the cleanup of abnormally terminated connections. Database Writer DBWR Writes database blocks to datafiles. Log Writer LGWR Writes the redo log entries to logfile. Checkpoint Process CKPT Signals DBWR to perform updates on all data and control files of the database. If not present, LGWR does this. System Monitor SMON Performs instance recovery and cleanup. Recovery Process RECO Resolves failures with the distributed option. Archival Process ARCH Copies full online redo log files to the archive device (if in ARCHIVELOG mode). A dedicated shadow thread is a separate dedicated server thread, which acts on behalf of a particular user. One thread is created for each user who connects to the database. Any request that a user has for the database is performed through the shadow thread for that user. Oracle8 Server version 8.0.4 supports a multithreaded server (MTS) environment. An MTS server thread can service requests from any client. When a shadow thread must read from the database, it checks to see if the data exists in the SGA. If the data exists in the SGA, the shadow thread reads it from the memory. If the data is not found in memory, the shadow thread goes directly to the datafiles and reads the data into the © 1998 Compaq Computer Corporation, All Rights Reserved Doc No ECG156/0398