I have an application that is reading data from disk and is using
proto buffers to create java objects. When doing performance analysis
I was surprised to find out that most of the time was spent in and
around proto buffers and not reading data from disk.
On profiling further (using yourkit) I found the following breakdown
of the function that was converting byte[] to a message:
1. Total - 13 sec
2. Decoding strings - 7 sec
3. <Message>.Builder.mergeFrom - 6 sec
Again I expected that decoding strings would be almost all the time
(although decoding here still seems slower than in C in my
experience). I am trying to figure out why mergeFrom method for this
message is taking 6 sec (own time). My message looks something like
this:
message Message {
enum SubMessageType {
TYPE1 = 1;
TYPE2 = 2;
...
}
required SubMessageType type = 1;
optional SubMessage1 subMessage1 = 2;
optional SubMessage2 subMessage2 = 3;
...
}
There are around 15 SubMessages. Each of the sub messages are
basically very simple messages with just one string field. Also from
the profiler reading sub messages is taking around 7 sec which is all
in String decoding (as I mentioned above).
The code for <Message>.Builder.mergeFrom is basically just a loop
reading a tag and trying to match to one of the sub message types.
This loop would at most have 2 iterations (1 for the enum and 1 for
the sub messages). I am confused then how this method is taking up so
much time. I noticed that there were synthetic accessor warnings in
the proto-buffer generated code and some of that showed up in the
profiler as well (UnknownFieldSet.newBuilder...access$000). That
doesn't quite account for the whole time though.
In your experience is this expected? Am I doing something wrong? Can I
add any options or write the message differently to make it more
efficient. I will appreciate any insight.
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