Indices are really helpful on databases that hold many thousands
of rows and are searched frequently. On the other hand, indices
are harmful on tables which are frequently written to because not
only the actual entry needs to be updated but also the index.
So expecially in the particular case of the attributes tables,
the index is of more harm than use because we write updates all
the time and never read it. Removing the index on the attributes
table reduces the disk io footprint of the zigbee db by 30%.
As the other tables are mostly sitting still all the time, the
index doesn't really do much harm either in terms of disk io,
but it increases the database size, while not providing much
benefit, as those entries are also only read once at startup
and the tables are reasonably small (a few hundreds).
Michael Zanetti
Simon Stürz