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Note: The following description applies both to Postgres-XC and PostgreSQL if not described explicitly. You can read PostgreSQL as Postgres-XC except for version number, which is specific to each product.
libpq is reentrant and thread-safe by default. You might need to use special compiler command-line options when you compile your application code. Refer to your system's documentation for information about how to build thread-enabled applications, or look in src/Makefile.global for PTHREAD_CFLAGS and PTHREAD_LIBS. This function allows the querying of libpq's thread-safe status:
One thread restriction is that no two threads attempt to manipulate the same PGconn object at the same time. In particular, you cannot issue concurrent commands from different threads through the same connection object. (If you need to run concurrent commands, use multiple connections.)
PGresult objects are normally read-only after creation, and so can be passed around freely between threads. However, if you use any of the PGresult-modifying functions described in Section 30.11 or Section 30.13, it's up to you to avoid concurrent operations on the same PGresult, too.
The deprecated functions PQrequestCancel and
PQoidStatus are not thread-safe and should not be
used in multithread programs. PQrequestCancel
can be replaced by PQcancel.
PQoidStatus can be replaced by
PQoidValue.
If you are using Kerberos inside your application (in addition to inside
libpq), you will need to do locking around
Kerberos calls because Kerberos functions are not thread-safe. See
function PQregisterThreadLock in the
libpq source code for a way to do cooperative
locking between libpq and your application.
If you experience problems with threaded applications, run the program in src/tools/thread to see if your platform has thread-unsafe functions. This program is run by configure, but for binary distributions your library might not match the library used to build the binaries.