VERITAS File System 4.1 Administrator's Guide

Quick I/O for Databases
Quick I/O Functionality and Performance
Chapter 11162
Avoiding Kernel Write Locks
When database I/O is performed via the write() system call, each system call acquires and
releases a write lock inside the kernel. This lock prevents simultaneous write operations on
the same file. Because database systems usually implement their own locks for managing
concurrent access to files, write locks unnecessarily serialize I/O operations. Quick I/O
bypasses file system locking and lets the database server control data access.
Avoiding Double Buffering
Most database servers implement their own buffer cache and do not need the system buffer
cache. So the memory used by the system buffer cache is wasted, and results in data being
cached twice: first in the database cache and then in the system buffer cache. By using direct
I/O, Quick I/O does not waste memory on double buffering. This frees up memory, which the
database server buffer cache can use, and thereby increasing performance.