check_mysql.c: Detect running mysqldump

When checking a slave, if the IO Thread or the SQL Thread are stopped, check for running mysqldump threads, return STATE_OK if there is any.
Requires PROCESS privilege to work (else the mysqldump thread(s) would not be detected).

Enlarged SLAVERESULTSIZE to fit "Mysqldump: in progress" at the end of the string.
Got a NULL pointer in row[seconds_behind_field] instead of the "NULL" string when a mysqldump is running [mysql 5.7.34 + libmariadb3 10.3.31], so added a check for that.

1 files changed, 26 insertions, 6 deletions

diff --git a/plugins/check_mysql.c b/plugins/check_mysql.c
index 0cba50e6..5b9a4fec 100644
--- a/plugins/check_mysql.c
+++ b/plugins/check_mysql.c
@@ -34,7 +34,7 @@ const char *progname = "check_mysql";
 const char *copyright = "1999-2011";
 const char *email = "devel@monitoring-plugins.org";
 
-#define SLAVERESULTSIZE 70
+#define SLAVERESULTSIZE 96
 
 #include "common.h"
 #include "utils.h"
@@ -89,6 +89,8 @@ static const char *metric_counter[LENGTH_METRIC_COUNTER] = {
         "Uptime"
 };
 
+#define MYSQLDUMP_THREADS_QUERY "SELECT COUNT(1) mysqldumpThreads FROM information_schema.processlist WHERE info LIKE 'SELECT /*!40001 SQL_NO_CACHE */%'"
+
 thresholds *my_threshold = NULL;
 
 int process_arguments (int, char **);
@@ -275,11 +277,29 @@ main (int argc, char **argv)
                         /* Save slave status in slaveresult */
                         snprintf (slaveresult, SLAVERESULTSIZE, "Slave IO: %s Slave SQL: %s Seconds Behind Master: %s", row[slave_io_field], row[slave_sql_field], seconds_behind_field!=-1?row[seconds_behind_field]:"Unknown");
 
-                        /* Raise critical error if SQL THREAD or IO THREAD are stopped */
+                        /* Raise critical error if SQL THREAD or IO THREAD are stopped, but only if there are no mysqldump threads running */
                         if (strcmp (row[slave_io_field], "Yes") != 0 || strcmp (row[slave_sql_field], "Yes") != 0) {
-                                mysql_free_result (res);
-                                mysql_close (&mysql);
-                                die (STATE_CRITICAL, "%s\n", slaveresult);
+                                MYSQL_RES *res_mysqldump;
+                                MYSQL_ROW row_mysqldump;
+                                unsigned int mysqldump_threads = 0;
+
+                                if (mysql_query (&mysql, MYSQLDUMP_THREADS_QUERY) == 0) {
+                                        /* store the result */
+                                        if ( (res_mysqldump = mysql_store_result (&mysql)) != NULL) {
+                                                if (mysql_num_rows(res_mysqldump) == 1) {
+                                                        if ( (row_mysqldump = mysql_fetch_row (res_mysqldump)) != NULL) {
+                                                                mysqldump_threads = atoi(row_mysqldump[0]);
+                                                        }
+                                                }
+                                                /* free the result */
+                                                mysql_free_result (res_mysqldump);
+                                        }
+                                }
+                                if (mysqldump_threads == 0) {
+                                        die (STATE_CRITICAL, "%s\n", slaveresult);
+                                } else {
+                                        strlcat (slaveresult, " Mysqldump: in progress", SLAVERESULTSIZE);
+                                }
                         }
 
                         if (verbose >=3) {
@@ -291,7 +311,7 @@ main (int argc, char **argv)
                         }
 
                         /* Check Seconds Behind against threshold */
-                        if ((seconds_behind_field != -1) && (strcmp (row[seconds_behind_field], "NULL") != 0)) {
+                        if ((seconds_behind_field != -1) && (row[seconds_behind_field] != NULL && strcmp (row[seconds_behind_field], "NULL") != 0)) {
                                 double value = atof(row[seconds_behind_field]);
                                 int status;