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Global Buffer Memory Leaks (DBMS only)
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Q:

We are using an older version of DBMS, and we were trying to use global buffers. However, after some time has passed, the DBMS monitor would crash. What is causing the DBMS monitor to die?

 

A:

Global buffers were introduced in version 4.3 to reduce I/O by allowing multiple processes to share data in-memory. Global buffers are allocated out of system global pages by the DBMS monitor process when a database is opened (either by the DBO/OPEN command or by the first process that attaches to the database). When the database is closed, the monitor process should unmap the global pages it had allocated during the open.

Under some circumstances, the DBMS monitor process would fail to release all global pages it had previously allocated. This resulted in a "memory leak" which could ultimately cause the database monitor to consume all available global pages. Once this happens, it would be necessary to shut down the DBMS monitor in order to free the global pages and resume database operations. This problem has been fixed in DBMS 4.3a, 5.0, and 5.1a.

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