CDB(5) FreeBSD File Formats Manual CDB(5)
NAME
cdb - format of the constant database
DESCRIPTION
The cdb database format provides a space-efficient (key,value) database.
The format doesn't allow updates in any convenient form. The file
overhead is around 5 bytes per key and 5 bytes per entry. Keys are not
stored and it is the responsibility of the caller to validate matches.
The index structure is based on a minimal perfect hash table, so exactly
one entry has to be checked for a match.
General Format
The header record of a cdb database consists of the following:
struct header_cdb {
uint8_t magic[7];
uint8_t version;
uint8_t description[16];
uint32_t data_size;
uint32_t entries;
uint32_t entries_index;
uint32_t seed;
};
All fields are in Little Endian byte order.
This is followed by a description of the hash function of entries_index
records. The size of each index entry is the logarithm of entries to
base 256, rounded up.
The index records are followed by the start offsets of the entries,
followed by data_size. The offsets are relative to the end of the offset
record table and are monotonically increasing. The size of each offset
record is the logarithm of data_size to base 256, rounded up.
The offset table is followed by the entries in order. No separation or
padding is added.
Limitations
The cdb file format is by design intended for a database that can be
mapped into memory. The hard limit for the number of entries and keys is
3435973836. The total size of all values must be smaller than 4GiB.
SEE ALSO
cdbr(3), cdbw(3)
HISTORY
Support for the cdb format first appeared in NetBSD 6.0.
AUTHORS
The cdbr and cdbw functions have been written by Joerg Sonnenberger
<
[email protected]>.
FreeBSD 14.1-RELEASE-p8 April 27, 2010 FreeBSD 14.1-RELEASE-p8