Hello guys,
PostgreSQL 8.3.5. Compiled and installed on Slackware 10.2, kernel 2.6.15.
We have a transaction based system that creates a new process every time a
user connects (just fork()s, no exec()s). Each of these processes has several
threads. Some database connections are opened before the threads are created
(this is part of the basic design of the system), but each tread only uses one
specific connection assigned to it, no "cross" connection use.
We are using Embedded SQL in C mainly located in 1 source module, accessed
from all threads using function calls. Each thread is of course passing its
allocated connection name in these calls.
However, we have had some problems of database calls locking up or crashing
the program. In the investigation of one of these crashes we had to dig deep
into the source of the ecpg library. In doing this we have been wondering why
the descriptors are not connection specific when most other db accesses are. It
seems that if the db connection is not opened within the thread itself, the
descriptor to be used is randomly chosen among opened connections. Specifically
we are wondering about the reason for the descriptor name to be statically
assigned at compile time (fixed text) and not a variable that could then be
given a connection related name.
One strange thing about the behaviour of our program is that it "seems" to
run ok on some machines but crashes reproducible on others. All these systems
are having the same hardware (HP based PCs) with exactly the same Linux and
PostgreSQL installation.
To try to visualise our problem, I have included some pseudo code of our
program flow below.
What we would like to know is the philosophy of not having descriptors being
connection specific and whether this will change or not.
Leif
DB access module:
.
Db_Open( char *conn )
{
EXEC SQL EXEC SQL BEGIN DECLARE SECTION;
const char *dbname = _dbname;
const char *dbuser = _dbuser;
const char *_thisDbConn = conn;
EXEC SQL END DECLARE SECTION;
EXEC SQL CONNECT TO :dbname AS :_thisDbConn USER :dbuser;
if( sqlca.sqlcode ) {
return( SQLErr_NotOpen );
}
EXEC SQL AT :_thisDbConn SET AUTOCOMMIT TO OFF;
if( sqlca.sqlcode ) {
return( SQLErr_NotOpen );
}
return( SQLErr_Ok );
}
Db_SQLExec( char *conn, char *stmt )
{
.
EXEC SQL ALLOCATE DESCRIPTOR execdesc;
.
.
EXEC SQL DEALLOCATE DESCRIPTOR execdesc;
.
}
Main source module:
pthread_t thA = 0;
pthread_t thB = 0;
main()
{
.
char *connA = "connA";
char *connB = "connB";
Db_Open( connA );
Db_Open( connB );
.
.
rval = pthread_create( &thA, NULL, funcA, NULL );
.
rval = pthread_create( &thB, NULL, funcB, NULL );
.
Db_Close( connA );
Db_Close( connB );
}
Various modules:
funcA( ... )
{
.
// Many calls like:
Db_SQLExec( "connA", <some SQL statement> );
.
}
funcB( ... )
{
.
// Many calls like:
Db_SQLExec( "connB", <some SQL statement> );
.
}
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