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error encountered in windows when libpq sends large query string to server

From: Ranen Ghosh <rghosh(at)westernavionics(dot)com>
To: pgsql-interfaces(at)postgresql(dot)org
Subject: error encountered in windows when libpq sends large query string to server
Date: 2005-11-03 15:22:55
Message-ID: 436A2B4F.6000005@westernavionics.com (view raw or flat)
Thread:
Lists: pgsql-interfaces
A winsock error is encountered when attempting to send a large query 
string (over 60 megabytes after escape characters were added) to a 
postgresql server from windows XP.  The error was observed in using the 
pyPgSQL python binding to libpq, but was traced to libpq.

In python, the error was:

libpq.OperationalError? 
<https://www.comcube.ca/trac/comcube/wiki/OperationalError> could not 
send data to server: No buffer space available (0x00002747/10055)

<traceback object at 0x00CC5260>


from postgresql-8.0.3/src/interfaces/libpq/win32.c: WSAENOBUFS, "No 
buffer space available"
from 
http://msdn.microsoft.com/library/default.asp?url=/library/en-us/winsock/winsock/windows_sockets_error_codes_2.asp: 
WSAENOBUFS 10055

The problem is client side: when a smaller query string is successfully 
sent, a series of TCP packets are exchanged between the client and the 
server; but when the large query string is sent, there are no TCP 
packets exchanged.  The query-string-size at which the error occurs is 
somewhere around 64 megabytes after escaping.

The problem occurs in postgresql-8.0.3/src/interfaces/libpq/fe-misc.c, 
in pqSendSome(), which calls pqsecure_write() in 
postgresql-8.0.3/src/interfaces/libpq/fe-secure.c. In this function, the 
send() function call fails when the length of the buffer reaches 
approximately 64M.

The code for postgresql-8.1beta3 does not seem to implement the above 
mentioned functions differently.

As the error is client side, and the error message is a winsock error, I 
had thought that the most likely solution was changing an attribute of 
the socket (perhaps with setsockopt()) to expand the buffer space 
available). The default value of SO_SNDBUF is 8192. Changing this value 
to 0 or to 16384 (and confirming that the value had in fact changed 
internally) had no effect on the problem, however.

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