Thread: Small Bug in pgstat display during recovery conflict resolution

Hi Simon, Hi all,


if (!logged && (wait_s > 0 || wait_us > 500000))
{       const char *oldactivitymsg;       int                     len;
       oldactivitymsg = get_ps_display(&len);       snprintf(waitactivitymsg, sizeof(waitactivitymsg),
     "waiting for max_standby_delay (%u s)",                        MaxStandbyDelay);
set_ps_display(waitactivitymsg,false);       if (len > 100)               len = 100;       memcpy(waitactivitymsg,
oldactivitymsg,len);
 
       pgstat_report_waiting(true);
       logged = true;
}
..
if (logged)
{       set_ps_display(waitactivitymsg, false);       pgstat_report_waiting(false);
}

That doesnt work because get_ps_display returns the internal buffer. This 
leads to the situation that after conflict resolution the 
"waiting for max_standby_delay ..."
message is displayed until the next segment starts where its replaced
again by the 
"... recovering ..." line.

Additionally the old code may print unintialized memory if get_ps_displayreturns a string without a \0 terminator.

The attached patch fixes that.

Andres

Committed, thanks.

On Sun, 2010-02-07 at 21:47 +0100, Andres Freund wrote:
> Hi Simon, Hi all,
> 
> 
> if (!logged && (wait_s > 0 || wait_us > 500000))
> {
>         const char *oldactivitymsg;
>         int                     len;
> 
>         oldactivitymsg = get_ps_display(&len);
>         snprintf(waitactivitymsg, sizeof(waitactivitymsg),
>                          "waiting for max_standby_delay (%u s)",
>                          MaxStandbyDelay);
>         set_ps_display(waitactivitymsg, false);
>         if (len > 100)
>                 len = 100;
>         memcpy(waitactivitymsg, oldactivitymsg, len);
> 
>         pgstat_report_waiting(true);
> 
>         logged = true;
> }
> ..
> if (logged)
> {
>         set_ps_display(waitactivitymsg, false);
>         pgstat_report_waiting(false);
> }
> 
> That doesnt work because get_ps_display returns the internal buffer. This 
> leads to the situation that after conflict resolution the 
> "waiting for max_standby_delay ..."
> message is displayed until the next segment starts where its replaced
> again by the 
> "... recovering ..." line.
> 
> Additionally the old code may print unintialized memory if get_ps_display
>  returns a string without a \0 terminator.
> 
> The attached patch fixes that.
> 
> Andres
-- Simon Riggs           www.2ndQuadrant.com