I downloaded the NetBSD fossil repository at

<http://ftp.NetBSD.org/pub/NetBSD/misc/repositories/fossil/src.fossil>,

opened it with `fossil open ../src.fossil', chose a file at random, and
tried to annotate it with `cd src/sys/dev/usb && fossil annotate
uark.c'.  It took over an hour before `fossil annotate' began to write
any output.

Around forty minutes in, I ktraced the fossil process for a minute or
so, which revealed that almost everything it was doing was pwrite.
iostat reported that it was hammering the disk -- writing 20 megabytes
per second.  (Nothing else on the machine was doing substantial disk
I/O then.)

After it completed, I started it up again with `fossil --sqltrace
annotate uark.c', and all the output I have seen so far is of the form

SELECT a.pid, b.mtime FROM plink a LEFT JOIN plink b ON b.cid=a.pid WHERE a.cid=N;
INSERT OR IGNORE INTO ok VALUES(M);

where N and M are positive integers that are nearby one another and
both are decrementing but don't seem to be equal.