I/O for cooked files for dbspace chunks

On UNIX, you can control the use of direct I/O for cooked files used for dbspace chunks.

On UNIX, you can allocate disk space in two ways:

When dbspaces reside on raw disk devices (also called character-special devices), the database server uses unbuffered disk access. A raw disk directly transfers data between the database server memory and disk without also copying data.

While you should generally use raw disk devices on UNIX systems to achieve better performance, you might prefer to use cooked files, which are easier to allocate and manage than raw devices. If you use cooked files, you might be able to get better performance by enabling the Informix® direct I/O option.

In addition, Informix supports a separate concurrent I/O option on AIX® operating systems. If you enable concurrent I/O on AIX, you get both unbuffered I/O and concurrent I/O. With concurrent I/O, writing to two parts of a file can occur concurrently. (On some other operating systems and file systems, enabling direct I/O also enables concurrent I/O as part of the same file system direct I/O feature.)

To determine the best performance, perform benchmark testing for the dbspace and table layout on your system.

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