A few words about the shared memory and files

Even if running in the Classic (isolated process) mode, Firebird needs some data to be available to all the running server processes. There are four kinds of information that must be shared:

• Lock table. It’s the vital part of the lock manager and its primary goal is to synchronize access to various resources that can be read or modified simultaneously.
• Event table. Every time a posted event is committed, the server needs to find all the subscribers and redirect the event delivery to processes handling the appropriate user connections.
• Monitoring snapshot. It keeps the latest known state of all the running worker processes and it gets updated once some user connection attempts to access the monitoring tables in a new transaction.
• Trace configuration. It contains the information required for the worker processes to react on the currently active tracing events and log the appropriate notifications.

Continue reading at Dmitry Yemanov’s blog.