1 files changed, 37 insertions, 1 deletions
diff --git a/doc/vmod-dbrw.texi b/doc/vmod-dbrw.texi
index 734dadb..6a987ed 100644
--- a/doc/vmod-dbrw.texi
+++ b/doc/vmod-dbrw.texi
@@ -129,13 +129,20 @@ This latter form can be used in contexts where the variable reference is
 immediately followed by a letter, digit or underscore, to prevent it
 from being counted as a part of the name. Special syntax is available
 for substituting default values and invoking built-in functions during
 the expansion of the query. @xref{Expansions}, for a detailed
 description of these.
 
+@anchor{X-VMOD-DBRW-Error}
+@vindex X-VMOD-DBRW-Error
 Having undergone expansions, the query is sent to the database server.
+If the query returns no records or if an error occured, @code{rewrite}
+returns empty string.  In case of error, it also sets the HTTP header
+@samp{X-VMOD-DBRW-Error: 1}.  It can be used in VLC code to provide a
+special handling for such failures.
+
 The returned set of records (if non-empty) is processed depending on the
 number of fields it contains.
 
 @cindex result interpretation
 @anchor{result interpretation}
 @cindex strict matching
@@ -163,13 +170,13 @@ subexpression in @var{regexp}.  For compatibility with the traditional
 usage, the @code{\@var{digit}} notation is also allowed.  The
 resulting value is then returned to the caller.
 
 @cindex flags
 @anchor{flags}
 Optional @var{flags} column is a comma-separated list of flags that
-modify regular expression handling:
+control the matching algorithm.
 
 @table @samp
 @kindex NC
 @kindex nocase
 @cindex regular expression, case-insensitive
 @cindex case-insensitive regular expression
@@ -180,12 +187,17 @@ Treat @var{regexp} as case-insensitive regular expression.
 @kindex case
 @cindex regular expression, case-sensitive
 @cindex case-sensitive regular expression
 @item case
 Treat @var{regexp} as case-sensitive (default).
 
+@kindex eq
+@cindex exact matching
+@item eq
+Use exact string matching.
+
 @kindex QSA
 @kindex qsappend
 @cindex query string handling
 @cindex append query string
 @item QSA
 @itemx qsappend
@@ -206,12 +218,18 @@ the original @var{value}.
 @cindex redirection code
 @cindex status code
 @item redirect=@var{code}
 @item R=@var{code}
 On success, set the @samp{X-VMOD-DBRW-Status} header to @var{code},
 which must be a valid HTTP status code. 
+
+@kindex regex
+@cindex regular expression matching
+@item regex
+Use regular expression matching.  This is the default.  This flag is
+provided for completeness sake, as a counterpart of @samp{eq}.
 @end table
 
 If @var{regexp} or @var{value} is NULL, strict matching is assumed
 (@pxref{strict matching}).
 
 If @var{flags} is NULL, it is ignored.
@@ -698,12 +716,30 @@ sub vcl_synth @{
 @end example
 
 The @code{X-VMOD-DBRW-Status} header, if set, contains the status code to be
 returned to the client (@pxref{X-VMOD-DBRW-Status}).  Notice the use
 of the @command{vmod_std} module to cast it to integer.
 
+If an error occured during the rewrite, it is recommended to not
+cache the response.  This way the next request will call rewrite again
+and eventually complete the rewriting.  This can be achieved using the
+following @code{vcl_backend_response} fragment:
+
+@example
+@group
+sub vcl_backend_response
+@{
+    if (bereq.http.X-VMOD-DBRW-Error == "1") @{
+        set beresp.uncacheable = true;
+        return (deliver);
+    @}
+@}
+@end group
+@end example
+
+
 @node Reporting Bugs
 @chapter How to Report a Bug
 
   Email bug reports to @email{gray@@gnu.org}.
 
   As the purpose of bug reporting is to improve software, please be