Re: MySQL fallback servers

Hi Simon!

On Mon, 03 Aug 2009, Simon Horman wrote:

> 1. Provide a Signed-off-by line as per the instructions at
>    section 5 of http://linux.yyz.us/patch-format.html
> 
> 2. Provide a patch to perdition/perditiondb.5.
>    A separate patch with a Signed-off-by is fine.
>    Although if you'd prefer to revise the patch
>    below that is fine too.

Okay, here we go:

The attached patch provides the feature to fall back from one MySQL
server to a list of others, it the first one is not reachable.

Signed-off-by: Roland Rosenfeld <[email protected]>

diff -urNpd perdition-1.17.1/perdition/db/mysql/perditiondb_mysql.c perdition-1.17.1-ro/perdition/db/mysql/perditiondb_mysql.c
--- perdition-1.17.1/perdition/db/mysql/perditiondb_mysql.c	2005-06-22 07:50:04.000000000 +0200
+++ perdition-1.17.1-ro/perdition/db/mysql/perditiondb_mysql.c	2009-07-31 10:51:24.000000000 +0200
@@ -42,7 +42,9 @@
 
 
 static vanessa_dynamic_array_t *a=NULL;
-static char *dbhost          = PERDITIONDB_MYSQL_DEFAULT_DBHOST;
+static vanessa_dynamic_array_t *dbhosts_array=NULL;
+static size_t dbhosts_count = 0;
+static char *dbhosts         = PERDITIONDB_MYSQL_DEFAULT_DBHOSTS;
 static char *dbname          = PERDITIONDB_MYSQL_DEFAULT_DBNAME;
 static unsigned int dbport   = PERDITIONDB_MYSQL_DEFAULT_DBPORT;
 static char *dbtable         = PERDITIONDB_MYSQL_DEFAULT_DBTABLE;
@@ -92,10 +94,10 @@ int dbserver_fini(void){
  * dbserver_init
  * Parse options string.
  * pre: options_str: Options string. String is of the form
- * [dbhost[:port[:dbname[:dbtable[:dbuser[:dbpwd[:dbsrvcol[:dbusercol[:dbportcol]]]]]]]]]
+ * [dbhost1[,dbhost2[,...]][:port[:dbname[:dbtable[:dbuser[:dbpwd[:dbsrvcol[:dbusercol[:dbportcol]]]]]]]]]
  * post: Options string is parsed if not null into 
  *       static vanessa_dynamic_array_t a and 
- *       static char *dbhost, *dbname, *dbtable, *dbuser, *dbpwd are
+ *       static char *dbhosts, *dbname, *dbtable, *dbuser, *dbpwd are
  *       set to pointers insiside a or defaults as neccesary.
  * return:  0 on success
  *         -1 on db access error
@@ -130,8 +132,16 @@ int dbserver_init(char *options_str){
    }
 
    count=vanessa_dynamic_array_get_count(a);
-   if(count>PERDITIONDB_MYSQL_DBHOST){ 
-     dbhost=vanessa_dynamic_array_get_element(a, PERDITIONDB_MYSQL_DBHOST); 
+   if(count>PERDITIONDB_MYSQL_DBHOSTS){ 
+     dbhosts=vanessa_dynamic_array_get_element(a, PERDITIONDB_MYSQL_DBHOSTS); 
+     if ((dbhosts_array = vanessa_dynamic_array_split_str(dbhosts, 
+			  PERDITIONDB_MYSQL_HOSTS_DELIMITER)) == NULL) {
+       VANESSA_LOGGER_DEBUG("vanessa_dynamic_array_split_str");
+       a=NULL;
+       free(tmp_str);
+       return(-1);
+     }
+     dbhosts_count = vanessa_dynamic_array_get_count(dbhosts_array);
    }
    if(count>PERDITIONDB_MYSQL_DBNAME){ 
      dbname=vanessa_dynamic_array_get_element(a, PERDITIONDB_MYSQL_DBNAME); 
@@ -211,6 +221,7 @@ int dbserver_get(
    MYSQL_ROW row;
    char sqlstr[PERDITIONDB_MYSQL_QUERY_LENGTH];
    size_t servername_len;
+   size_t hcnt = 0;
 
    rc = mysql_init(&db);
    if(!rc){  
@@ -219,7 +230,13 @@ int dbserver_get(
      return(-1);
    }
 
-   rc = mysql_real_connect(&db,dbhost,dbuser,dbpwd,dbname,dbport,NULL,0);
+   while (hcnt < dbhosts_count 
+        && !(rc=mysql_real_connect(&db,
+                        vanessa_dynamic_array_get_element(dbhosts_array, hcnt),
+                        dbuser,dbpwd,dbname,dbport,NULL,0))) {
+     perditiondb_mysql_log("mysql_connect", &db);
+     hcnt++;
+   }
    if(!rc){  
      perditiondb_mysql_log("mysql_connect", &db);
      mysql_close(&db);
diff -urNpd perdition-1.17.1/perdition/db/mysql/perditiondb_mysql.h perdition-1.17.1-ro/perdition/db/mysql/perditiondb_mysql.h
--- perdition-1.17.1/perdition/db/mysql/perditiondb_mysql.h	2005-06-22 07:50:04.000000000 +0200
+++ perdition-1.17.1-ro/perdition/db/mysql/perditiondb_mysql.h	2009-07-31 09:49:25.000000000 +0200
@@ -43,8 +43,9 @@
 #include <vanessa_adt.h>
 
 #define PERDITIONDB_MYSQL_FIELD_DELIMITER   ':'
+#define PERDITIONDB_MYSQL_HOSTS_DELIMITER   ','
 #define PERDITIONDB_MYSQL_MAX_SLEEP         1800
-#define PERDITIONDB_MYSQL_DEFAULT_DBHOST    "localhost"
+#define PERDITIONDB_MYSQL_DEFAULT_DBHOSTS   "localhost"
 #define PERDITIONDB_MYSQL_DEFAULT_DBPORT    0
 #define PERDITIONDB_MYSQL_DEFAULT_DBNAME    "dbPerdition"
 #define PERDITIONDB_MYSQL_DEFAULT_DBTABLE   "tblPerdition"
@@ -54,7 +55,7 @@
 #define PERDITIONDB_MYSQL_DEFAULT_DBSRVCOL  "servername"
 #define PERDITIONDB_MYSQL_DEFAULT_DBPORTCOL "port"
 
-#define PERDITIONDB_MYSQL_DBHOST    0
+#define PERDITIONDB_MYSQL_DBHOSTS   0
 #define PERDITIONDB_MYSQL_DBPORT    1
 #define PERDITIONDB_MYSQL_DBNAME    2
 #define PERDITIONDB_MYSQL_DBTABLE   3
diff -urNpd perdition-1.17.1/perdition/perditiondb.5 perdition-1.17.1-ro/perdition/perditiondb.5
--- perdition-1.17.1/perdition/perditiondb.5	2005-06-22 07:50:05.000000000 +0200
+++ perdition-1.17.1-ro/perdition/perditiondb.5	2009-08-12 09:34:55.000000000 +0200
@@ -332,7 +332,14 @@ the arguments to avoid confusion.
 Database servers may be grouped together for higher performance
 or high availability by using ODBC and accessing
 them using the ODBC module.
-
+.P
+.B Multiple MySQL Servers
+.P
+It is possible to specify multiple MySQL servers by specifying them,
+comma separated (without any space), in the dbhost column.  In this
+case all MySQL servers need to have an identical configuration,
+because all other options are shared.  If the first server is not
+reachable, perdition will fall back to the second etc.
 .P
 .B
 POSTGRESQL

-- 
Roland Rosenfeld  -  Content Delivery  -  NED  -  Technik
NetCologne Gesellschaft für Telekommunikation mbH  -  HRB 25580, AG Köln
Am Coloneum 9   50829 Köln   Tel.: +49-221-2222-373   Fax: +49-221-2222-7373
Geschäftsführer: Werner Hanf, Karl-Heinz Zankel
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