Initialization and Shutdown

The class ss_m is the core of the SSM interface. Creating an instance of ss_m starts the SSM. Destroying the ss_m instance causes the SSM to shutdown. Details on initialization and shutdown are available in init(ssm).

When the SSM is started, it processes configuration options described below and initializes all the SSM data structures. This initialization includes allocation of the buffer pool. The buffer pool is located in shared memory, so the operating system must have shared-memory support to accommodate the size of the buffer pool. Next, the SSM checks the log to see if recovery is needed. If so, it follows the steps discussed in the recovery section below.

 

Setting SSM Configuration Options

The SSM has several configuration options that must be set before it is started with the ss_m constructor. These options include such things as buffer pool sizes and location of the log. Many have default values. Those without default values must be set or the SSM will fail.

sm_bufpoolsize

no-default
The size of buffer pool in K-bytes. The minimum value is 64. Increasing the size may decrease the amount of I/O done by the SSM.

sm_logdir

no-default
The SSM currently uses Unix files for log storage. This option sets the path name of the directory where log files will be placed.

sm_logsize

10000
The maximum size, in K-bytes, of the log. All updates by transactions are logged, so the log size puts a limit on how much work any transaction can do. See the section on logging for a discussion of log space usage.

sm_logging

yes
This options controls whether or not logging is performed at all. Turning it off, by setting it to no, is used primarily for evaluating logging performance. No recovery or transaction rollback can be performed if logging is off.

sm_diskrw

diskrw
The path name (in the Unix file system) of the program forked by the SSM to perform asynchronous I/O, normally SHROOT/bin/diskrw.

sm_locktablesize

64000
The number of buckets in the hash table used by the lock manager.

sm_backgroundflush

yes
This option controls whether or not there is a background thread started to flush the buffer pool periodically.

sm_errlog

- (stderr)
The location to send error logging messages. The default is the standard error file. Other options are syslogd (to syslog daemon), or to a specific filename.

sm_errlog_level

error
The level of error logging detail. Possible values (from least amount of logging to most amount) are none emerg fatal alert internal error warning info debug.

 

Adding VAS-Specific Options

A VAS will often have options of its own that need to be set. The SSM provides an options facility, options(common) for this purpose. Included with the option facility are functions to set options from the program command line and from files containing configuration information. A discussion of how to use the options facility is included in Configuration Options section of the VAS Tutorial.