Identifying a message in emit_log_hook.

Hello.

I'm planning to change the error level of a specific error
message.  We can use emit_log_hook for this purpose but we have
no reliable means to identify what a message is.

For messages without valid sqlerrcode, filename:lineno could be
used to identify but lineno is too unstable.  One possible and
most straightforward way to solve this is defining identifiers
covering all error messages but such identifiers are too hard to
manage.  ErrorData.message could also be used but NLS translation
and placeholders prevent it from being identified by simple means
like strcmp(3).

As a solution for this problem, I'd like to porpose to have an
additional member in the struct ErrorData to hold a message id,
that is, the format string for errmsg(). This is not best but
useful enough.

It is somewhat a crude way, but the attached small patch would
do.

Is there any opinions or suggestions?

regards,

-- 
Kyotaro Horiguchi
NTT Open Source Software Center
diff --git a/src/backend/utils/error/elog.c b/src/backend/utils/error/elog.c
index 9005b26..2d13101 100644
--- a/src/backend/utils/error/elog.c
+++ b/src/backend/utils/error/elog.c
@@ -801,6 +801,7 @@ errmsg(const char *fmt,...)    CHECK_STACK_DEPTH();    oldcontext =
MemoryContextSwitchTo(edata->assoc_context);
+    edata->message_id = fmt;    EVALUATE_MESSAGE(edata->domain, message, false, true);
MemoryContextSwitchTo(oldcontext);
@@ -830,6 +831,7 @@ errmsg_internal(const char *fmt,...)    CHECK_STACK_DEPTH();    oldcontext =
MemoryContextSwitchTo(edata->assoc_context);
+    edata->message_id = fmt;    EVALUATE_MESSAGE(edata->domain, message, false, false);
MemoryContextSwitchTo(oldcontext);
@@ -853,6 +855,7 @@ errmsg_plural(const char *fmt_singular, const char *fmt_plural,    CHECK_STACK_DEPTH();
oldcontext= MemoryContextSwitchTo(edata->assoc_context);
 
+    edata->message_id = fmt_singular;    EVALUATE_MESSAGE_PLURAL(edata->domain, message, false);
MemoryContextSwitchTo(oldcontext);
@@ -1361,6 +1364,7 @@ elog_finish(int elevel, const char *fmt,...)    recursion_depth++;    oldcontext =
MemoryContextSwitchTo(edata->assoc_context);
+    edata->message_id = fmt;    EVALUATE_MESSAGE(edata->domain, message, false, false);
MemoryContextSwitchTo(oldcontext);
@@ -1420,6 +1424,7 @@ format_elog_string(const char *fmt,...)    oldcontext = MemoryContextSwitchTo(ErrorContext);
+    edata->message_id = fmt;    EVALUATE_MESSAGE(edata->domain, message, false, true);
MemoryContextSwitchTo(oldcontext);
diff --git a/src/include/utils/elog.h b/src/include/utils/elog.h
index 326896f..4df76da 100644
--- a/src/include/utils/elog.h
+++ b/src/include/utils/elog.h
@@ -354,6 +354,7 @@ typedef struct ErrorData    char       *detail_log;        /* detail error message for server log
only*/    char       *hint;            /* hint message */    char       *context;        /* context message */
 
+    const char *message_id;        /* message id of .message */    char       *schema_name;    /* name of schema */
char      *table_name;        /* name of table */    char       *column_name;    /* name of column */