Use mc.buf as scratchpad for intarpolation

[methane]

benchmark                  old ns/op     new ns/op     delta
BenchmarkInterpolation     1900          1363          -28.26%

benchmark                  old allocs     new allocs     delta
BenchmarkInterpolation     2              1              -50.00%

benchmark                  old bytes     new bytes     delta
BenchmarkInterpolation     448           160           -64.29%

[methane]

I can remove last one allocation: Stop using mc.exec() and build packet directly.
But it may be dirty a little. May I do it?

[arnehormann]

I'm opposed to it, I like having the packet building in one place.
But I do like the part where you use mc.buf.takeSmallBuffer (or takeCompleteBuffer) as a scratch space... the packet construction code doesn't need it yet.
By the way - why did you change buffer.go?

[julienschmidt]

bufSize

[methane]

fixed

[julienschmidt]

What allocation exactly are you trying to eliminate?

[methane]

This allocation is removed.

[julienschmidt]

I mean by stop using mc.exec()

[arnehormann]

I think he means the conversion of the query from []byte to string to []byte

[methane]

Yes, I mean it.
Future Go may be able to optimize it, but I think Go 1.5 will not.

[julienschmidt]

Draft it. If it doesn't get too dirty, I would be fine with it.

[arnehormann]

And if that is fine, it can be applied in other areas, too.
We could e.g. have a variable-cached version of a full COM_QUIT and COM_STMT_CLOSE packet. The former can be sent as is, the letter only has to have the sequence number changed...
But that scatters the network Write calls to multiple places and makes maintaining the driver a little harder.

[methane]

@arnehormann

But I do like the part where you use mc.buf.takeSmallBuffer (or takeCompleteBuffer) as a scratch space... the packet construction code doesn't need it yet.

packet size is len(query) + 4. This size is used just after interpolate.
So I think reserving same size is good idea.

By the way - why did you change buffer.go?

fixed.

[methane]

Now interpolateParams() uses mc.buf.takeCompleteBuffer().
And I've eliminated estimateParamLength().

[arnehormann]

LGTM!