Thread

1. fetch_search_path() and elog.c

   Ferruccio Zamuner <nonsolosoft@diff.org> — 2005-07-11T07:53:37Z

   Hi,
   
   I need to have in the log_line_prefix the search_path where the query 
   has run.
   So last week I've started to read elog.c and I was thinking about a 
   small patch there using a new "%S" option.
   
   First I've introduced a small code:
         case 'S':
           {
               List *search_path = fetch_search_path(false);
               if (search_path != NIL) {
                   ListCell   *l;
                   foreach(l, search_path)
                      {
                          char       *nspname;
   
                          nspname = get_namespace_name(lfirst_oid(l));
                          if (nspname)                    /* watch out for 
   deleted namespace */
                              {
                                   appendStringInfo(buf, "%s ", nspname);
                                   pfree(nspname);
                             }
                     }
                   list_free(search_path);
               }
               break;
           }
   
   but in this way postgres was starting with a core dump writing on log.
   
   Then I've add some code, and now it starts but it kills the postgres 
   process as soon as a query has sent to log:
   
   $ diff -u elog.c elog_new.c
   --- elog.c      Sat Mar 12 02:55:15 2005
   +++ elog_new.c  Sun Jul 10 10:16:35 2005
   @@ -67,7 +67,8 @@
    #include "tcop/tcopprot.h"
    #include "utils/memutils.h"
    #include "utils/guc.h"
   -
   +#include "catalog/namespace.h"
   +#include "catalog/pg_type.h"
   
    /* Global variables */
    ErrorContextCallback *error_context_stack = NULL;
   @@ -1444,6 +1445,32 @@
                           case '%':
                                   appendStringInfoChar(buf, '%');
                                   break;
   +                               /* */
   +                       case 'S':
   +                               /* estrae il search_path */
   +                         if (MyProcPort && (MyProcPort->commandTag != 
   NULL)) {
   +                           char *cmd=MyProcPort->commandTag;
   +                           if ((strcasecmp(cmd,"SELECT")== 0) || 
   (strcasecmp(cmd,"INSERT")== 0) || (strcasecmp(cmd,"UPDATE")== 0) || 
   (strcasecmp(cmd,"DELETE")== 0)) {
   +                            
   +                           }
   +                         }
   +                         break;
   +List *search_path = fetch_search_path(false);
   +                             if (search_path != NIL) {
   +                               ListCell   *l;
   +                               foreach(l, search_path)
   +                                 {
   +                                   char       *nspname;
   +
   +                                   nspname = 
   get_namespace_name(lfirst_oid(l));
   +                                   if (nspname)                    /* 
   watch out for deleted namespace */
   +                                     {
   +                                       appendStringInfo(buf, "%s ", 
   nspname);
   +                                       pfree(nspname);
   +                                     }
   +                                 }
   +                               list_free(search_path);
   +                             }
                           default:
                                   /* format error - ignore it */
                                   break;
   
   And here there is the client output:
   
   bash-2.05a$ psql prova -U pgsql
   Welcome to psql 8.0.3, the PostgreSQL interactive terminal.
   
   Type:  \copyright for distribution terms
          \h for help with SQL commands
          \? for help with psql commands
          \g or terminate with semicolon to execute query
          \q to quit
   
   prova=# select * from prova;
   server closed the connection unexpectedly
           This probably means the server terminated abnormally
           before or while processing the request.
   The connection to the server was lost. Attempting reset: Failed.
   !>
   
   Where can I start to understand which checks I've missed and how to gain 
   the output I need?
   
   
   Thank you in advance,                \ferz
   ---
   NonSoLoSoft - http://www.nonsolosoft.com/
   
   

2. Re: fetch_search_path() and elog.c

   Tom Lane <tgl@sss.pgh.pa.us> — 2005-07-11T13:25:30Z

   Ferruccio Zamuner <nonsolosoft@diff.org> writes:
   > I need to have in the log_line_prefix the search_path where the query 
   > has run.
   > So last week I've started to read elog.c and I was thinking about a 
   > small patch there using a new "%S" option.
   
   There's no chance of that code working when not inside a transaction;
   which means that in most of the scenarios where you really want a log
   entry to be made, it will fail.
   
   			regards, tom lane
   
   

3. Re: fetch_search_path() and elog.c

   Ferruccio Zamuner <nonsolosoft@diff.org> — 2005-07-11T16:22:26Z

   Tom Lane wrote:
   
   >Ferruccio Zamuner <nonsolosoft@diff.org> writes:
   >  
   >
   >>I need to have in the log_line_prefix the search_path where the query 
   >>has run.
   >>So last week I've started to read elog.c and I was thinking about a 
   >>small patch there using a new "%S" option.
   >>    
   >>
   >
   >There's no chance of that code working when not inside a transaction;
   >which means that in most of the scenarios where you really want a log
   >entry to be made, it will fail.
   >
   >			regards, tom lane
   >  
   >
   Now I've found a simpler solution:
   
   case 'S':
                       /* estrae il search_path */
                 if (namespace_search_path != NULL)
                   appendStringInfo(buf, "%s ", namespace_search_path);
                 break;
   
   It seems to work.
   
   But I would like to understand why previous code was wrong.
   
   

4. Re: fetch_search_path() and elog.c

   Alvaro Herrera <alvherre@alvh.no-ip.org> — 2005-07-11T17:04:37Z

   On Mon, Jul 11, 2005 at 06:22:26PM +0200, Ferruccio Zamuner wrote:
   
   > Now I've found a simpler solution:
   > 
   > case 'S':
   >                    /* estrae il search_path */
   >              if (namespace_search_path != NULL)
   >                appendStringInfo(buf, "%s ", namespace_search_path);
   >              break;
   > 
   > It seems to work.
   > 
   > But I would like to understand why previous code was wrong.
   
   I think it was because you were doing catalog lookups (the
   get_namespace_name() function, etc), and these don't work outside a
   transaction.
   
   -- 
   Alvaro Herrera (<alvherre[a]alvh.no-ip.org>)
   "¿Cómo puedes confiar en algo que pagas y que no ves,
   y no confiar en algo que te dan y te lo muestran?" (Germán Poo)