Sybase 12.4.2 manual 424, Raw partitions versus file systems, Multi-user database access

Overview of memory use

Raw partitions versus file systems

For UNIX systems, databases using “cooked” file systems rather than raw partitions may require another 30% of the remaining memory to handle file buffering by the operating system. Windows NT file systems do not have the same overhead as UNIX file systems. However, Windows NT and some UNIX systems may benefit from reserving a significant portion of memory for the file system to better handle I/O operations. For more information, see the Adaptive Server IQ Installation and Configuration Guide for your platform.

Multi-user database access

For multi-user queries of a database, Adaptive Server IQ needs about 10MB per “active” user. An active user is defined as one that simultaneously accesses or queries the database. For example, 30 users may be connected to Adaptive Server IQ, but only 10 or so may be actively using a database at any one time.

Memory requirements for loads

Adaptive Server IQ also requires a portion of memory separate from the buffer caches to perform loads operations, synchronization, and deletions. This memory is used for buffering I/O for flat files. Adaptive Server IQ uses memory to buffer a read from disk. The size of this read equals the BLOCK FACTOR multiplied by the size of the input record. BLOCK FACTOR is an option of the LOAD TABLE command. With the default value of 10,000, an input row of data of 200 bytes results in 2MB total that Adaptive Server IQ uses for buffering I/O. This memory is required only when loading from flat files, not for inserts from a database.

Memory for thread stacks

Processing threads require a small amount of memory. The more IQ processing threads you use, the more memory needed. The -iqmtserver switch controls the number of threads for IQ.

If you have a large number of users, the memory needed for Catalog Store processing threads also increases, although it is still relatively small. The -gnswitch controls Catalog Store processing threads.

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