#include <db.h> int DB->set_partition(DB * db, u_int32_t parts, DBT *keys, u_int32_t (*db_partition_fcn) (DB *db, DBT *key));
Set up partitioning for a database. Partitioning may be used on either BTREE or HASH databases. Partitions may be specified by either a set of keys specifying a range of values in each partition, or with a callback function that returns the number of the partition to put a specific key. Partition range keys may only be specified for BTREE databases.
Partitions are implemented as separate database files and can help reduce contention within a logical database. Contention can come from multiple threads of control accessing database pages simultaneously. Typically these pages are the root of a btree and the metadata page which contains allocation information in both BTREE and HASH databases. Each partition has its own metadata and root pages.
The DB->set_partition() method can not
be used with a sliced database.
Exactly one of the parameters keys and partition_fcn must be NULL.
The parts parameter is the number of partitions to create. The value must be greater than or equal to 2, and smaller than 1000000.
The keys parameter is an array of DBT structures containing the keys that specify the range of key values to be stored in each partition. Each key specifies the minimum value that may be stored in the corresponding partition. The number of keys must be one less than the number of partitions specified by the parts parameter since the first partition will hold any key less than the first key in the array.
The db_partition_fcn parameter is the application-specified partitioning function. The function returns an integer which will be used modulo the number of partitions specified by the parts parameter. The function will be called with two parameters:
db
The db parameter is the database handle.
key
The key parameter is the key for which a partition number should be returned.