[DERBY-2118] Change some boundary checks in ArrayInputStream to ASSERTs to improve performance

• Type: Improvement
• Status: Closed
• Priority: Trivial
• Resolution: Fixed
• Affects Version/s: 10.2.1.6
• Fix Version/s: 10.3.1.4
• Bug behavior facts: Performance
• Assignee: Dyre Tjeldvoll
• Reporter: Dyre Tjeldvoll
• Created: 27/Nov/06 10:01
• Updated: 29/Jun/09 14:22
• Resolved: 01/Jun/07 10:55

Description

Profiling shows that a significant amount of CPU is spent doing boundary checking in ArrayInputStream.setPosition() and ArrayInputStream.setLimit(). These checks appear to be there to detect error conditions, so it seems more appropriate to make them ASSERTs. Especially since they are so expensive.

DTrace analysis seems to confirm that these methods get called very frequently:

Knut Anders Hatlen wrote the following in a message on derby-dev:

FYI, I just ran the DERBY-1961 test clients and traced them with a
DTrace script that printed how often each method was called. For the
join client, ArrayInputStream.setPosition() was the most frequently
called method (43837.7 calls/tx). For the single-record select client,
it was third (58.4 calls/tx), only beaten by Object.<init>() and
DDMWriter.ensureLength(). I think this means that setPosition() is the
engine method that is most frequently called, at least in read-mostly
transactions. ArrayInputStream.setLimit() also appeared near the top
of the list. See http://wiki.apache.org/db-derby/Derby1961MethodCalls
for the details.