load_db/1¶

load_db(+ Files)*

Load a database of ground facts. All facts must take up the same amount of storage, so that a fact $I$ can be accessed at position P[I-1]. This representation thus stores the facts as a huge continuous array, the so-called mega clause.

See for a motivation for this technique. YAP implements this optimization by default whenever it loads a large number of facts (see Yap_BuildMegaClause(PredEntry ap) ) for the details. On the other hand, loading the data-base will cause fragmentation because individual facts facts need extra headers ands tails, and because often new atoms will be stored in the Symbol Table, see LookupAtom(const char atom). The main advantage of load_db//11 is that it allocates the necessary memory only once. Just doing this may halve total memory usage in large in-memory database-oriented applications.

note:
Implementation

YAP implements load_db//11 as a two-step non-optimised process. First, it counts the nmuber of facts and checks their size. Second, it allocates and fills the memory. The first step of the algorithm is implemented by dbload_get_space(), and the second by dbload_add_facts().

db_files//11 itself is just a call to load_files//22.