Faster Creation of Transaction Logs Using Templates

Information concerning ongoing transactions is saved on a continual basis in a transaction log file. A chronological series of transaction log files is maintained during the operation of the c-tree Server. Transaction log files containing the actual transaction information are saved as standard files. They are given names in sequential order, starting with L0000001.FCS (which can be thought of as "active c-tree Server log, number 0000001") and incrementing sequentially (i.e., the next log file is L0000002.FCS, etc.). By default, the c-tree Server saves up to four active logs at a given time.

A new transaction log is automatically filled with 0xff (to ensure known contents), extended, and flushed to ensure log space is available. This process occurs during log write operations which means that the log file is tied up during this fill/extension processing. This can lead to increased latency for transactions that are in progress when log extension occurs.

With the transaction log template feature enabled, a new empty log template named L0000000.FCT is created at server startup to serve as a log template. The first actual full size log, L0000001.FCS, is copied from the template and a blank log, L0000002.FCT, is copied from the template. Whenever a new log is required, the corresponding blank log file is renamed from L000000X.FCT to L000000X.FCS and, asynchronously, the next blank log, L000000Y.FCT, is copied from the template.

This feature is effective only for use in very high speed, high throughput systems where it is desirable to be more than one log ahead in case the template copy operation runs slowly.

Enabling Log Templates

Enable the log template feature by specifying the server keyword LOG_TEMPLATE in the server configuration file. The usage is:

LOG_TEMPLATE <n>

where <n> is the number of log templates you want the server to maintain. The default is 0, which means no use of log templates. For instance, a value of two (2) means that two blank logs (L0000002.FCT and L0000003.FCT) would be created at first server startup in addition to the template (L0000000.FCT).

Prior to using the log template feature, existing transaction logs must be deleted in order to cause the server to create log templates. To do this, shut down the server cleanly and delete Lnnnnnnn.FCS, S0000000.FCS, and S0000001.FCS. When the server is restarted after adding this keyword, startup may take longer due to creation of template log files (*.FCT).

Limitations

Log templates are not supported when mirrored logs or log encryption is in use.