db-derby-dev mailing list archives

Site index · List index
Message view « Date » · « Thread »
Top « Date » · « Thread »
From "Knut Anders Hatlen (JIRA)" <j...@apache.org>
Subject [jira] Commented: (DERBY-3192) Cache session data in the client driver
Date Mon, 21 Jan 2008 13:13:34 GMT

    [ https://issues.apache.org/jira/browse/DERBY-3192?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12561002#action_12561002
] 

Knut Anders Hatlen commented on DERBY-3192:
-------------------------------------------

In the writeup, I read this:
> Most of the overhead seems to come from the PKGNAMCSN instance variable which by itself
uses 76 bytes

It does however seem like DRDA allows this variable to be skipped.

DRDA, ver. 4, vol 1, p 10:

> PKGNAM, PKGNAMCSN, PKGNAMCT
> The length is no longer fixed and is based on the lengths of the RDBNAM,
> RDBCOLID, and PKGID contained therein. As of SQLAM Level 7, the
> PKGNAMCSN instance variable is optional. If not specified, the PKGSN is
> required to identify the package section number. The package name and
> consistency token defaults to the last set of values specified on the connection.

DRDA, ver. 4, vol 1, p 463:

> CU15 The fully qualified package name and package consistency token are not required
to be
> specified on every SQL-related request. If the package name and consistency token are
> not specified on a request, the last request that specified the package name and
> consistency token is used to identify the package name and consistency token for the
> request. The package section number is not optional and is required if the package
> name and consistency token are not specified. If the package name and consistency
> token were not specified on a previous request to establish the default, the request
is
> rejected by the application server with a conversational protocol error with the error
> code set to X'20' (default package name not established).

> Cache session data in the client driver
> ---------------------------------------
>
>                 Key: DERBY-3192
>                 URL: https://issues.apache.org/jira/browse/DERBY-3192
>             Project: Derby
>          Issue Type: Improvement
>          Components: JDBC, Network Client, Network Server, Performance, SQL
>    Affects Versions: 10.3.1.4
>            Reporter: Dyre Tjeldvoll
>            Assignee: Dyre Tjeldvoll
>         Attachments: derby-3192-test.fup1.diff, derby-3192-test.fup2.diff, derby-3192-test.v1.diff,
derby-3192-test.v1.stat, derby-3192.prelim1.diff
>
>
> The reason for doing this is to avoid a rather
> substantial performance hit observed when the client driver is used
> together with an appserver that uses connection pooling. There are two
> problems:
> 1) The connection pool will compare the isolation level it has
> stored for the connection with the value returned from
> Connection.getTransactionIsolation() each and every time someone
> requests a new connection from the pool.
> 2) The users of the connection pool (ab)use it to avoid having to keep
> track of their current connection. So each time a query needs to be
> executed a call to the connection pool's getConnection() method is
> made. Getting a connection from the connection pool like this also
> means that a new PreparedStatement must be prepared each time.
> The net result is that each query results in the following sequence:
> getConnection()
> getTransactionIsolation() --> roundtrip + lookup in server's statement cache
> prepareStatment()         --> roundtrip + lookup in server's statement cache
> executeQuery()            --> roundtrip
> Arguably this is a "user error" but when suggesting this I'm kindly
> informed that this works "just fine" with other datbases (such as
> PostgreSQL and ORACLE). 
> The reason why it works is that these databases do statement caching
> in the driver. I've tried to implement a very (too) simple statement
> cache in Derby's client driver and to re-enable caching of the
> isolation level (see
> https://issues.apache.org/jira/browse/DERBY-1148). With these changes
> I observe a marked performance improvement when running with appserver
> load. 
> A proper statment cache cannot be implemented without knowing what the
> current schema is. If the current schema has changed since the
> statement was prepared, it is no longer valid and must be evicted from
> the cache.
> The problem with caching both the isolation level and the current schema in
> the driver is that both can change on the server without the client
> detecting it (through SQL and XA and possibly stored procedures).
> I think this problem can be overcome if we piggy-back the information we would 
> like to cache on messages going back to the client. This can be done by
> utilizing the EXCSQLSET DRDA command. According to the DRDA spec (v4, volume 3, 
> page 359-360) it is possible to add one or more SQLSTT objects after SQLCARD in the reply,
> I think it would be possible to cache additional session information when this becomes
relevant.  It
> would also be possible to use EXCSQLSET to batch session state changes
> going from the client to the server.

-- 
This message is automatically generated by JIRA.
-
You can reply to this email to add a comment to the issue online.


Mime
View raw message