Add note about how to make the SRF detoasted arguments live accross calls.

Andrew Gierth and Ali Akbar

diff --git a/doc/src/sgml/xfunc.sgml b/doc/src/sgml/xfunc.sgml
index 97a56562d3e40293b8bee91df37de90f974844a2..b85f2adc453eb5bd862d5b317952fee5eb738ede 100644 (file)
--- a/doc/src/sgml/xfunc.sgml
+++ b/doc/src/sgml/xfunc.sgml
@@ -2981,6 +2981,20 @@ SRF_RETURN_DONE(funcctx)
      multi_call_memory_ctx while doing the first-call setup.
     
 
+    
+     
+      While the actual arguments to the function remain unchanged between
+      calls, if you detoast the argument values (which is normally done
+      transparently by the
+      PG_GETARG_xxx macro)
+      in the transient context then the detoasted copies will be freed on
+      each cycle. Accordingly, if you keep references to such values in
+      your user_fctx, you must either copy them into the
+      multi_call_memory_ctx after detoasting, or ensure
+      that you detoast the values only in that context.
+     
+    
+
     
      A complete pseudo-code example looks like the following: