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As NDBs use inverted-list indexes, bulk record addition, update, or deletion can be slow. This is because of the large number of physical file updates required to manage all the keyed field indexes.
To allow fast loading (in particular), an NDB can be placed in LOAD MODE. In LOAD MODE, no keys (other than the optional sequence key) are maintained. This greatly improves record add speed.
When in LOAD MODE, records can be added, updated, deleted, retrieved, or scanned. However, none of these operations use keys. This means that GET or SEQ by a key is not allowed. Only RID access is permitted.
The only way to take an NDB out of LOAD MODE is to use the NDB ALTER command. This command, using the BLDX DB option, reads all the NDB data records, extracts all keys, sorts them, and writes them in a single pass. It checks for errors (for example, unique key violation) and, when finished, resets LOAD MODE.
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