Controls the fraction of unmasked unique seeds that are indexed by the makeudb_search or makeudb_ublast command, expressed as a percentage. Value must be between 0 and 100, default is 100. With values < 100, the database will be smaller and searches will be faster, at the expense of a loss in sensitivity. Note that the database size scaling is not linear, so with -dbaccel 90 the database might be half as big.
This option can be useful for reducing the memory requirements of a search. To improve speed, it it is generally better to use the -accel option which uses query-specific statistics to prioritize seeds. With -dbaccel, averaged statistics are used which tend to have lower sensitivity for a given query. With indexes for usearch_global and usearch_local, the -dbstep option is usually preferred for reducing memory use.