Tips and tricks for optimal application performance using Oracle databases.
Especially usage and functions of my Swiss army knife "Panorama" for Oracle performance analysis are explained.
A common pitfall while using sequences in Oracle-DB is forgetting to define sequence caching. The default for sequences is cache size = 0. That means, every sequence.nextval operation triggers a single write operation on dictionary table sys.SEQ$. Especially if frequently calling sequence.nextval uncached sequences may cause significant performance degradation. Frequently calling sequence.nextval in parallel sessions may lead to ramdom lock scenarios in library cache. Setting a cache size for a sequence may heavy increase performance of nextval-operations. There's a minimal memory overhead for caching a sequence because all that's needed is a counter to increase in SGA memory and a upper limit. If this limit is reached with the counter, the upper limit is increased by cache size and the new upper limit is written down once to SEQ$. The possible drawback for sequence caching is that you loose all your values between the current value and the highest cached value if yo...
It's very common that firewalls are terminating idle TCP sessions after a limited time, often after approximately one hour. Possible problem If you have a long running SQL or PL/SQL program and the firewall terminates your apparently idle TCP session this may lead to the following scenario: the database is not able to send result to client. After reaching the TCP-timeout the database server terminates the DB-Session the client program stays in socket read forever waiting for the database response Oracle's full solution: SQLNET.EXPIRE_TIME=x in sqlnet.ora Oracle's solution for this problem is setting parameter SQLNET.EXPIRE_TIME=x in sqlnet.ora where x are the minutes between keep alive packets on idle sessions that inform the firewall that this session is always alive. SQLNET.EXPIRE_TIME hast to be set in the sqlnet.ora of your RDBMS' ORACLE_HOME. Normally $ORACLE_HOME/network/admin. If you have a grid infrastructure setting SQLNET.EXPIRE_TIME in sqlnet...
Sometimes it is useful to know about the network latency of client connections to database. Normally this would be done with the established network tools tnsping, ping, traceroute, tcptraceroute etc. from client or DB server side. But what if there is only SQL access to the DB server and no access to the client? This post shows how the network latency can be estimated using the recordings from ASH if the application uses a certain access pattern. The network latency between client and database server can be estimated by the number of number of SQL executions of a single session between two ASH snapshots. If an application executes the same very short running SQL against the DB over and over again in a loop, then: it is a bad architecture approach for the application because the network latency will cause a significant overhead for application performance however, this behavior gives a possibility for a weak estimation of the network latency between client and database ser...
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