RE: [Patch] PQconnectPoll() is blocked if target_session_attrs isread-write

From: Matsumura, Ryo [mailto:matsumura.ryo@jp.fujitsu.com]
> Detail:
> If target_session_attrs is set to read-write, PQconnectPoll() calls
> PQsendQuery("SHOW transaction_read_only") althogh previous return value
> was PGRES_POLLING_READING not WRITING.

The current code probably assumes that PQsendQuery() to send "SHOW transaction_read_only" shouldn't block, because the
messageis small enough to fit in the socket send buffer.  Likewise, the code in CONNECTION_AWAITING_RESPONSE case sends
authenticationdata using pg_fe_sendauth() without checking for the write-ready status.  OTOH, the code in
CONNECTION_MADEcase waits for write-ready status in advance before sending the startup packet.  That's because the
startuppacket could get large enough to cause pqPacketSend() to block.
 

So, I don't think the fix is necessary.

> In result, PQsendQuery() may be blocked in pqsecure_raw_write().

FWIW, if PQsendQuery() blocked during connection establishment, I think it should block in poll() called from .... from
pqWait(),because the libpq's socket is set non-blocking.
 


Regards
Takayuki Tsunakawa