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Code review for pgstat_get_crashed_backend_activity patch.

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Avoid possibly dumping core when pgstat_track_activity_query_size has a
less-than-default value; avoid uselessly searching for the query string
of a successfully-exited backend; don't bother putting out an ERRDETAIL if
we don't have a query to show; some other minor stylistic improvements.
This commit is contained in:
Tom Lane
2011-10-21 16:36:04 -04:00
parent 5ac5980744
commit f9c92a5a3e
5 changed files with 66 additions and 47 deletions
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54
src/backend/postmaster/pgstat.c
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@@ -2760,27 +2760,33 @@ pgstat_get_backend_current_activity(int pid, bool checkUser)
* pgstat_get_crashed_backend_activity() -
*
* Return a string representing the current activity of the backend with
* the specified PID. Like the function above, but reads shared memory with
* the expectation that it may be corrupt. Returns either a pointer to a
* constant string, or writes into the 'buffer' argument and returns it.
* the specified PID. Like the function above, but reads shared memory with
* the expectation that it may be corrupt. On success, copy the string
* into the "buffer" argument and return that pointer. On failure,
* return NULL.
*
* This function is only intended to be used by postmaster to report the
* query that crashed the backend. In particular, no attempt is made to
* This function is only intended to be used by the postmaster to report the
* query that crashed a backend. In particular, no attempt is made to
* follow the correct concurrency protocol when accessing the
* BackendStatusArray. But that's OK, in the worst case we'll return a
* corrupted message. We also must take care not to trip on ereport(ERROR).
*
* Note: return strings for special cases match pg_stat_get_backend_activity.
* BackendStatusArray. But that's OK, in the worst case we'll return a
* corrupted message. We also must take care not to trip on ereport(ERROR).
* ----------
*/
const char *
pgstat_get_crashed_backend_activity(int pid, char *buffer,
int len)
pgstat_get_crashed_backend_activity(int pid, char *buffer, int buflen)
{
volatile PgBackendStatus *beentry;
int i;
beentry = BackendStatusArray;
/*
* We probably shouldn't get here before shared memory has been set up,
* but be safe.
*/
if (beentry == NULL || BackendActivityBuffer == NULL)
return NULL;
for (i = 1; i <= MaxBackends; i++)
{
if (beentry->st_procpid == pid)
@@ -2790,26 +2796,29 @@ pgstat_get_crashed_backend_activity(int pid, char *buffer,
const char *activity_last;
/*
* We can't access activity pointer before we verify that it
* falls into BackendActivityBuffer. To make sure that the entire
* string including its ending is contained within the buffer,
* we subtract one activity length from it.
* We mustn't access activity string before we verify that it
* falls within the BackendActivityBuffer. To make sure that the
* entire string including its ending is contained within the
* buffer, subtract one activity length from the buffer size.
*/
activity_last = BackendActivityBuffer + BackendActivityBufferSize
- pgstat_track_activity_query_size;
- pgstat_track_activity_query_size;
if (activity < BackendActivityBuffer ||
activity > activity_last)
return "<command string corrupt>";
return NULL;
if (*(activity) == '\0')
return "<command string empty>";
/* If no string available, no point in a report */
if (activity[0] == '\0')
return NULL;
/*
* Copy only ASCII-safe characters so we don't run into encoding
* problems when reporting the message.
* problems when reporting the message; and be sure not to run
* off the end of memory.
*/
ascii_safe_strncpy(buffer, activity, len);
ascii_safe_strlcpy(buffer, activity,
Min(buflen, pgstat_track_activity_query_size));
return buffer;
}
@@ -2818,9 +2827,10 @@ pgstat_get_crashed_backend_activity(int pid, char *buffer,
}
/* PID not found */
return "<backend information not available>";
return NULL;
}
/* ------------------------------------------------------------
* Local support functions follow
* ------------------------------------------------------------