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Patch to cure O(N^2) behavior in libpq when reading a long 

message under a kernel that only returns one packet per recv() call.  This
didn't use to matter much, but it starts to get annoying with multi-megabyte
EXPLAIN VERBOSE responses...
This commit is contained in:
Tom Lane 1999-09-13 03:00:19 +00:00
parent ad4a574b00
commit 3ec5232363
1 changed files with 25 additions and 3 deletions
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28
src/interfaces/libpq/fe-misc.c
View File

@ -24,7 +24,7 @@
*
*
* IDENTIFICATION
* $Header: /cvsroot/pgsql/src/interfaces/libpq/fe-misc.c,v 1.29 1999/08/31 01:37:36 tgl Exp $
* $Header: /cvsroot/pgsql/src/interfaces/libpq/fe-misc.c,v 1.30 1999/09/13 03:00:19 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@ -307,6 +307,7 @@ pqReadReady(PGconn *conn)
int
pqReadData(PGconn *conn)
{
int someread = 0;
int nread;
if (conn->sock < 0)
@ -359,11 +360,11 @@ tryAgain:
/* Some systems return EAGAIN/EWOULDBLOCK for no data */
#ifdef EAGAIN
if (errno == EAGAIN)
return 0;
return someread;
#endif
#if defined(EWOULDBLOCK) && (!defined(EAGAIN) || (EWOULDBLOCK != EAGAIN))
if (errno == EWOULDBLOCK)
return 0;
return someread;
#endif
/* We might get ECONNRESET here if using TCP and backend died */
#ifdef ECONNRESET
@ -378,9 +379,30 @@ tryAgain:
if (nread > 0)
{
conn->inEnd += nread;
/*
* Hack to deal with the fact that some kernels will only give us
* back 1 packet per recv() call, even if we asked for more and there
* is more available. If it looks like we are reading a long message,
* loop back to recv() again immediately, until we run out of data
* or buffer space. Without this, the block-and-restart behavior of
* libpq's higher levels leads to O(N^2) performance on long messages.
*
* Since we left-justified the data above, conn->inEnd gives the
* amount of data already read in the current message. We consider
* the message "long" once we have acquired 32k ...
*/
if (conn->inEnd > 32768 &&
(conn->inBufSize - conn->inEnd) >= 8192)
{
someread = 1;
goto tryAgain;
}
return 1;
}
if (someread)
return 1; /* got a zero read after successful tries */
/*
* A return value of 0 could mean just that no data is now available,
* or it could mean EOF --- that is, the server has closed the