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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
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>43.3. Memory Management</A
></H1
><DIV
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><DL
><DT
><B
>Table of Contents</B
></DT
><DT
><A
HREF="spi-spi-palloc.html"
>SPI_palloc</A
>&nbsp;--&nbsp;allocate memory in the upper executor context</DT
><DT
><A
HREF="spi-realloc.html"
>SPI_repalloc</A
>&nbsp;--&nbsp;reallocate memory in the upper executor context</DT
><DT
><A
HREF="spi-spi-pfree.html"
>SPI_pfree</A
>&nbsp;--&nbsp;free memory in the upper executor context</DT
><DT
><A
HREF="spi-spi-copytuple.html"
>SPI_copytuple</A
>&nbsp;--&nbsp;make a copy of a row in the upper executor context</DT
><DT
><A
HREF="spi-spi-returntuple.html"
>SPI_returntuple</A
>&nbsp;--&nbsp;prepare to return a tuple as a Datum</DT
><DT
><A
HREF="spi-spi-modifytuple.html"
>SPI_modifytuple</A
>&nbsp;--&nbsp;create a row by replacing selected fields of a given row</DT
><DT
><A
HREF="spi-spi-freetuple.html"
>SPI_freetuple</A
>&nbsp;--&nbsp;free a row allocated in the upper executor context</DT
><DT
><A
HREF="spi-spi-freetupletable.html"
>SPI_freetuptable</A
>&nbsp;--&nbsp;free a row set created by <CODE
CLASS="FUNCTION"
>SPI_execute</CODE
> or a similar
  function</DT
><DT
><A
HREF="spi-spi-freeplan.html"
>SPI_freeplan</A
>&nbsp;--&nbsp;free a previously saved prepared statement</DT
></DL
></DIV
><P
>    
   <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> allocates memory within
   <I
CLASS="FIRSTTERM"
>memory contexts</I
>, which provide a convenient method of
   managing allocations made in many different places that need to
   live for differing amounts of time.  Destroying a context releases
   all the memory that was allocated in it.  Thus, it is not necessary
   to keep track of individual objects to avoid memory leaks; instead
   only a relatively small number of contexts have to be managed.
   <CODE
CLASS="FUNCTION"
>palloc</CODE
> and related functions allocate memory
   from the <SPAN
CLASS="QUOTE"
>"current"</SPAN
> context.
  </P
><P
>   <CODE
CLASS="FUNCTION"
>SPI_connect</CODE
> creates a new memory context and
   makes it current.  <CODE
CLASS="FUNCTION"
>SPI_finish</CODE
> restores the
   previous current memory context and destroys the context created by
   <CODE
CLASS="FUNCTION"
>SPI_connect</CODE
>.  These actions ensure that
   transient memory allocations made inside your procedure are
   reclaimed at procedure exit, avoiding memory leakage.
  </P
><P
>   However, if your procedure needs to return an object in allocated
   memory (such as a value of a pass-by-reference data type), you
   cannot allocate that memory using <CODE
CLASS="FUNCTION"
>palloc</CODE
>, at
   least not while you are connected to SPI.  If you try, the object
   will be deallocated by <CODE
CLASS="FUNCTION"
>SPI_finish</CODE
>, and your
   procedure will not work reliably.  To solve this problem, use
   <CODE
CLASS="FUNCTION"
>SPI_palloc</CODE
> to allocate memory for your return
   object.  <CODE
CLASS="FUNCTION"
>SPI_palloc</CODE
> allocates memory in the
   <SPAN
CLASS="QUOTE"
>"upper executor context"</SPAN
>, that is, the memory context
   that was current when <CODE
CLASS="FUNCTION"
>SPI_connect</CODE
> was called,
   which is precisely the right context for a value returned from your
   procedure.
  </P
><P
>   If <CODE
CLASS="FUNCTION"
>SPI_palloc</CODE
> is called while the procedure is
   not connected to SPI, then it acts the same as a normal
   <CODE
CLASS="FUNCTION"
>palloc</CODE
>.  Before a procedure connects to the
   SPI manager, the current memory context is the upper executor
   context, so all allocations made by the procedure via
   <CODE
CLASS="FUNCTION"
>palloc</CODE
> or by SPI utility functions are made in
   this context.
  </P
><P
>   When <CODE
CLASS="FUNCTION"
>SPI_connect</CODE
> is called, the private
   context of the procedure, which is created by
   <CODE
CLASS="FUNCTION"
>SPI_connect</CODE
>, is made the current context.  All
   allocations made by <CODE
CLASS="FUNCTION"
>palloc</CODE
>,
   <CODE
CLASS="FUNCTION"
>repalloc</CODE
>, or SPI utility functions (except for
   <CODE
CLASS="FUNCTION"
>SPI_copytuple</CODE
>,
   <CODE
CLASS="FUNCTION"
>SPI_returntuple</CODE
>,
   <CODE
CLASS="FUNCTION"
>SPI_modifytuple</CODE
>, and
   <CODE
CLASS="FUNCTION"
>SPI_palloc</CODE
>) are made in this context.  When a
   procedure disconnects from the SPI manager (via
   <CODE
CLASS="FUNCTION"
>SPI_finish</CODE
>) the current context is restored to
   the upper executor context, and all allocations made in the
   procedure memory context are freed and cannot be used any more.
  </P
><P
>   All functions described in this section can be used by both
   connected and unconnected procedures.  In an unconnected procedure,
   they act the same as the underlying ordinary server functions
   (<CODE
CLASS="FUNCTION"
>palloc</CODE
>, etc.).
  </P
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