> What do you mean "just one syscall"? The entire point here is that it'd take more syscalls to send the same amount of data.
I mean that it messages are large enough more than 2K we will need 4 syscalls without copy it to the internal buffer, but currently we will copy 8K of messages and send it using 1 call. I think that under some threshold of packet length it is redundant to copy it to internal buffer and the data can be sent directly.
> It does strike me that with the v3 protocol, we do sometimes have cases
where internal_putbytes is reached with a fairly large "len". If we've
flushed out what's in PqSendBuffer to start with, and there's more than
a bufferload remaining in the source data, we could send the source
data directly to output without copying it to the buffer first.
That could actually result in *fewer* kernel calls not more, if "len"
is large enough. But I strongly doubt that a code path that nets
out to more kernel calls will win.
Yes, internal_putbytes can be updated to send data directly if the length is more than internal buffer size.
Aleksei Ivanov <iv.alekseii@gmail.com> writes:
> Yes, you are right there will be a separate call to send the data, but is
> copying data each time more costly operation than just one syscall?
What do you mean "just one syscall"? The entire point here is that it'd
take more syscalls to send the same amount of data.
It does strike me that with the v3 protocol, we do sometimes have cases
where internal_putbytes is reached with a fairly large "len". If we've
flushed out what's in PqSendBuffer to start with, and there's more than
a bufferload remaining in the source data, we could send the source
data directly to output without copying it to the buffer first.
That could actually result in *fewer* kernel calls not more, if "len"
is large enough. But I strongly doubt that a code path that nets
out to more kernel calls will win.
regards, tom lane