Because DTrace buffers some aggregation data in the kernel, space
might not be available when a new key is added to an aggregation.
In this case, the data is dropped, the counter is incremented, and
dtrace generates a message indicating an
aggregation drop. You should note that this situation rarely
occurs because DTrace keeps state information consisting of the
aggregation's key and intermediate results at user level, where
space can grow dynamically. In the unlikely event that an
aggregation drop occurs, you can increase the aggregation buffer
size by using the aggsize
option, which reduces
the likelihood of drops.
You can also use this option to minimize the memory footprint of
DTrace. As with any size option, aggsize
can be
specified with any size suffix. The resizing policy of this buffer
is dictated by the bufresize
option. For more
information about buffering, see Chapter 5, Buffers and Buffering.
An alternative method to eliminate aggregation drops is to
increase the rate at which aggregation data is consumed at the
user level. This rate defaults to once per second, and may be
explicitly tuned with the aggrate
option. As
with any rate option, aggrate
can be specified
with any time suffix, but defaults to rate-per-second. For more
information about the aggsize
option, see
Chapter 10, Options and Tunables.