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<title>37.4.Global Data in PL/Tcl</title>
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<a name="pltcl-global"></a>37.4.Global Data in PL/Tcl</h2></div></div></div>
<a name="id729763"></a><p> Sometimes it
is useful to have some global data that is held between two
calls to a function or is shared between different functions.
This is easily done since
all PL/Tcl functions executed in one session share the same
safe Tcl interpreter. So, any global Tcl variable is accessible to
all PL/Tcl function calls and will persist for the duration of the
SQL session. (Note that <span class="application">PL/TclU</span> functions likewise share
global data, but they are in a different Tcl interpreter and cannot
communicate with PL/Tcl functions.)
</p>
<p> To help protect PL/Tcl functions from unintentionally interfering
with each other, a global
array is made available to each function via the <code class="function">upvar</code>
command. The global name of this variable is the function's internal
name, and the local name is <code class="literal">GD</code>. It is recommended that
<code class="literal">GD</code> be used
for persistent private data of a function. Use regular Tcl global
variables only for values that you specifically intend to be shared among
multiple functions.
</p>
<p> An example of using <code class="literal">GD</code> appears in the
<code class="function">spi_execp</code> example below.
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