Set write through threshold for index file blocks

#include "btree.h"

int btthresh(BTA* btact, int threshold);

The btthresh function sets the write threshold for the btree index file associated with the btact context pointer. The threshold defines the number of updates on a block that will cause it to be written to disk. A value of zero (the default for a btree index) means that a block is not written to disk until the memory it occupies is required for a new block.

btthresh offers finer-grained control over disk writes than in previous versions of Btree, which was either only when necessary (in exclusive mode), or after every API call (in shared mode). The intention is to allow the application program to reduce the chance of lost data in a btree index should a hardware or software falure interrupt the running program before the indexes are closed and dirty blocks flushed to disk.

NB: If threshold is set to a small value, it may reduce performance of the BTree application.

A non-zero return code indicates an error occurred.