Hi All,
So I am looking for bottlenecks to explain slow response times in a Web
Objects server application and I have come up with the following plan for
monitoring database access. I am not sure this is the best way to do it,
please let me know what you think.
I extend WOApplication and in the constructor I set a new delegate to the
EODatabaseContext and add an observer to NSNotificationCenter:
---
MyDelegateAndObserver myDelegateAndObserver = ...
EODatabaseContext.setDefaultDelegate(myDelegateAndObserver);
NSNotificationCenter.defaultCenter().addObserver(
myDelegateAndObserver,
new NSSelector("hookIntoChannel", new Class[] {NSNotification.class}),
EODatabaseContext.DatabaseChannelNeededNotification,
null);
---
In the class MyDelegateAndObserver I defined "hookIntoChannel" from above
and the methods to capture notifications:
---
public void hookIntoChannel(NSNotification not){
final EODatabaseContext dbctxt = (EODatabaseContext)not.object();
final EODatabaseChannel channel = new EODatabaseChannel(dbctxt);
if(channel != null){
channel.adaptorChannel().setDelegate(this);
dbctxt.registerChannel(channel);
}
}
public boolean adaptorChannelShouldEvaluateExpression(EOAdaptorChannel
channel, EOSQLExpression expression){
/* thread safe logging: start of database round trip */
return true;
}
public void adaptorChannelDidEvaluateExpression(EOAdaptorChannel channel,
EOSQLExpression expression){
/* thread safe logging: end of database round trip iif expression is
UPDATE or INSERT */
}
public NSArray databaseContextDidFetchObjects(EODatabaseContext dbCtxt,
NSArray results, EOFetchSpecification fetchSpec, EOEditingContext ec){
/* threadsafe logging: end of database round trip for SELECT */
return null;
}
---
I store the above logging in a java.lang.ThreadLocal and once the WO
request is about to return (listen for
WOApplication.ApplicationDidDispatchRequestNotification) I can sum up the
number of database accesses and the total time spent waiting for database
IO.
Two thing worry me about this approach:
1) I am overwriting the DatabaseContext default delegate with a custom
delegate that will always answer adaptorChannelShouldEvaluateExpression=true
2) What kind of overhead am I looking at here ... I suppose I will find
out, but does this look like the kind of code you would include in a
production environment application?
I appreciate your input
-Kasper Frederiksen
ps.
I could not find this in the documentation so this is based on empirical
evidence :). This is the life cycle of a database access as seen from the
notifications sent to DatabaseContext and AdaptorChannel. I have noted
where I have chosen to consider the closest points to the start/end of the
database IO for the purpose of logging time spent.
For a SQL SELECT
===
1) databaseContextShouldFetchObjects:
2) databaseContextShouldSelectObjects:
3) adaptorChannelShouldSelectAttributes:
4) adaptorChannelShouldEvaluateExpression: start of database access
5) adaptorChannelDidEvaluateExpression:
6) adaptorChannelDidSelectAttributes:
7) adaptorChannelWillFetchRow:
8) adaptorChannelDidFetchRow: 7 and 8 may be repeated a number of times
7) adaptorChannelWillFetchRow:
9) adaptorChannelDidFinishFetching:
10) databaseContextDidFetchObjects: end of database access
For a SQL UPDATE or INSERT
===
1) adaptorChannelWillPerformOperations:
4) adaptorChannelShouldEvaluateExpression: start of database access
5) adaptorChannelDidEvaluateExpression: end of database access
6) adaptorChannelDidPerformOperations:
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