Database Configuration and Operation

The default configuration for the JMS IQ Manager database is as follows:

• The database resides in the following directory:..\logicalhost\is\domains\domain_1\stcms\instance_1

• The segment filenames are stcms*.dbs.

• The number of segments created initially for the database is 4.

• The size of each segment is 8 MBytes on Windows and 16 MBytes on UNIX.

• There is no limit to the number of segments that can be created.

When the JMS IQ Manager starts up, the database consists of four segments; the total size of the database is 32 MBytes on Windows and 64 MBytes on UNIX.

Figure 1–4 JMS IQ Manager Database Structure

On startup, the JMS IQ Manager performs the following operations:

1. It allocates sufficient disk space to hold the minimum number of segments.

   The preceding figure shows a JMS IQ Manager allocation of four segments, numbered 7ef325 through 7ef328.

2. As messages arrive, they are appended to the first segment until the segment is full.

   When a segment is full, the JMS IQ Manager stores subsequent messages in the first free segment.

   The preceding figure shows that the third segment, 7ef327 in file stcms7ef327.dbs, is almost full.

3. If no segment is free, the JMS IQ Manager allocates a new segment if possible.

4. Memory is released as soon as the consumer has acknowledged the message or committed the transaction.

5. When all messages in a segment have expired or been removed from their queues, the JMS IQ Manager cleans up the segment, freeing it for reuse.

   In the preceding figure , the first segment (7ef325) has several segments that are white, indicating the slot is marked eligible. The segment is therefore almost ready for cleanup.