Solaris 8 System Administration Supplement

DNLC Improvements

This functionality is updated in the Solaris 8 6/00 software release.

The Enhanced Directory Name Look-up Cache (DNLC) is enhanced in the Solaris 8 6/00 software release to provide improved performance when accessing files in large directories with 1,000 or more files. The information here adds to information on managing system performance found in "System Performance (Overview)" in System Administration Guide, Volume 2.

The DNLC is a general file system service that caches the most recently referenced directory names and their associated vnodes. UFS directory entries are stored linearly on disk. This means locating an entry requires searching each entry for the name. Adding a new entry requires searching the entire directory to ensure the name does not exist. To solve this performance problem, entire directories are cached in memory by the DNLC.

Another feature in this release is DNLC caching of file objects that have been looked up, but do not exist. This is known as negative caching, and is useful because some applications repeatedly test to see if a file exists or not.

The section that follows describes the new DNLC tunable parameters. These parameters are set optimally and should not be changed casually.

Note -

MAXUINT is the maximum value of an unsigned integer.

dnlc_dir_enable
Description: Enables large directory caching
Data Type: Unsigned integer
Default Value: 1 (enabled)
Range: 0 (disabled), 1 (enabled)
When to Change: Directory caching has no known problems, but if problems occur, then set dnlc_dir_enable to 0 to disable caching.

dnlc_dir_min_size
Description: Minimum number of entries cached for one directory
Data Type: Unsigned integer
Default Value: 40
Range: 0 to MAXUINT (no maximum)
When to Change: If performance problems occur with caching small directories, then increase dnlc_dir_min_size. Note that individual file systems might have their own range limits for caching directories. For instance, UFS limits directories to a minimum of ufs_min_dir_cache bytes (approximately 1024 entries), assuming 16 bytes per entry.

dnlc_dir_max_size
Description: Maximum number of directory entries before caching
Data Type: Unsigned integer
Default Value: MAXUINT (no maximum)
Range: 0 to MAXUINT
When to Change: If performance problems occur with large directories, then decrease dnlc_dir_max_size.