Question & Answer
Question
How to monitor the data dictionary cache and adjust the Dictionary Cache. The dictionary cache retrieves and caches information about the tables accessed by Informix. This includes information such as column names, data types, indexes, and extents. Although Informix also places the actual pages for the system catalog tables, also known as partition pages, in the buffer pool, the dictionary cache is always used and generally presents a huge performance advantage for repeated access to the table information
Answer
To improve performance the IDS database server stores table information read from system catalog tables in an area of memory called the data dictionary cache. The data dictionary cache uses a hash table to make locating this information fast.
A hash value is computed based on a table's name and is affected by how many slots the data dictionary cache has in it. Ideally we would like for each table to have a unique hash value but in real life this is nearly impossible.
When more than one table has the same hash value associated with it, values are stored in a linked list for that particular slot in the data dictionary cache.
This attached word document will explain how to monitor the data dictionary cache with onstat and how to spot potential performance problems and areas that may need improvement.
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Document Information
Modified date:
16 June 2018
UID
swg21686291