Performance Tuning for Content Manager

Chapter 8. Tuning DB2 for Content Manager 249

By setting LOGSECOND to -1, you will have no limit on the size of the unit of

work or the number of concurrent units of work. However, rollback (both at the

savepoint level and the unit of work level) could be very slow due to the need to

retrieve log files from the archive. Crash recovery could also be very slow for the

same reason. DB2 will write a message to the administration notification log to

warn you that the current set of active units of work has exceeded the primary log

files. This is an indication that rollback or crash recovery could be extremely slow.

Default values (range)

2 (-1; 0 - 254)

To update

Run the following DB2 command:

db2 update db cfg for <database name> using LOGSECOND <parameter value>

Our recommendation

The Content Manager installation program changes this value to 20 for Library

Server database and to 50 for Resource Manager database

In general, keep the default values.

Secondary log files do not require permanent file space, so there is not need to

change these values. If secondary log files begin to be used more frequently,

think about changing the values of LOGFILSIZ or LOGPRIMARY parameters.

8.6.38 Minimum commits before writing logs to disk (MINCOMMIT)

Impact

DB - High

Description

This parameter enables you to delay the writing of log records to disk until a

minimum number of commits has been performed. This delay helps to reduce the

database manager overhead associated with writing log records. As a result, this

might improve performance when you have multiple applications running against

a database, and many commits are requested by the applications within a very

short time frame.

This grouping of commits occurs when the value of MINCOMMIT is greater than 1

and when the number of applications connected to the database is greater than or

equal to the value of this parameter. When commit grouping is being performed,

application commit requests could be held until either one second has elapsed or

the number of commit requests equals the value of this parameter. If there is not

250 Performance Tuning for Content Manager

enough transaction work to do, the database manager will commit transactions

every second. Changes to the parameter value take effect immediately. There is

no need to wait until all applications are disconnected from the database.

Default values (range)

1 (1 - 25)

To update

Run the following DB2 command:

db2 update db cfg for <database name> using MINCOMMIT <parameter value>

Our recommendation

Use the default.

If you need to perform a large initial load operation prior to launching a new

Content Manager system, increasing this value temporarily will help reduce

logging file I/O.

In general, if your application requires large concurrent write activities, simple

SQL statements to process, and single row updates (such as daily load

operation), you might want to increase the default value. This will result in more

efficient logging file I/O from occurring less frequently, and will write more log

records each time it does occur.

Grouping the commits might compromise response time of small transactions,

because they have to wait until the minimum number of transactions is ready to

be committed.

You could also sample the number of transactions per second and adjust this

parameter to accommodate the peak number of transactions per second (or

some large percentage of it). Accommodating peak activity would minimize the

overhead of writing log records during transaction-intensive periods.

If you increase MINCOMMIT, you might also have to increase the LOGBUFSZ

parameter to avoid having a full log buffer force a write during these

transaction-intensive periods. In this case, the LOGBUFSZ should be equal to:

MINCOMMIT * (log space used, on average, by a transaction)