RE: libpq debug log

From: Kyotaro Horiguchi <horikyota.ntt@gmail.com>
> > (45)
> This looks like a fusion of PQtrace and PQtraceEX. By the way, the
> timestamp flag is needed at log emittion. So we can change the state
> anytime.
>
> PQtrace(conn, of);
> PQtraceSetFlags(conn, PQTRACE_SUPPRESS_TIMESTAMPS);
> <logging without timestamps>
> PQtraceSetFlags(conn, 0);
> <logging with timestamps>

I find this better because the application does not have to call PQuntrace() and PQtrace() again to enable/disable
timestampoutput, which requires passing the FILE pointer again.  (I don't imagine applications would repeatedly turn
loggingon and off in practice, though.) 


> > (46)
> >
> > If skipLogging is intended for use with backend -> frontend messages only,
> shouldn't it be placed in conn->b_msg?
>
> The name skipLogging is somewhat obscure. The flag doesn't inhibit all
> logs from being emitted.  It seems like it represents how far bytes
> the logging mechanism consumed for the limited cases. Thus, I think it
> can be a cursor variable like inCursor.
>
> If we have conn->be_msg->inLogged, for example, pqGetc and
> pqLogMessageByte1() are written as the follows.
>
> pqGetc(char *result, PGconn *conn)
> {
>     if (conn->inCursor >= conn->inEnd)
>         return EOF;
>
>     *result = conn->inBuffer[conn->inCursor++];
>
>     if (conn->Pfdebug)
>         pqLogMessageByte1(conn, *result);
>
>     return 0;
> }
>
> pqLogMessageByte1(...)
> {
>    switch()
>    {
>      case LOG_FIRST_BYTE:
>        /* No point in logging already logged bytes */
>        if (conn->be_msg->inLogged >= conn->inCursor)
>          return;
>    ...
>    }
>    conn->be_msg->inLogged = conn->inCursor;
> }

This looks better design because stuff like skipLogging is an internal state of logging facility whose use should be
restrictedto fe-logging.c. 

> (pqCheckInBufferSpace needs to adjust inLogged.)
>
> I'm not sure this is easier to read than the skipLogging.

I'd like Iwata-san to evaluate this and decide whether to take this approach or the current one.


Regards
Takayuki Tsunakawa