From 4feb72409a7a80f8f687022a3da45922bab456b1 Mon Sep 17 00:00:00 2001
From: Brian Kelly <brianpkelly46@gmail.com>
Date: Wed, 15 Jul 2015 13:53:19 -0400
Subject: [PATCH] write_redis plugin: Add option to limit sorted set size

---
 src/collectd.conf.pod | 10 ++++++++--
 src/write_redis.c     | 16 +++++++++++++++-
 2 files changed, 23 insertions(+), 3 deletions(-)

diff --git a/src/collectd.conf.pod b/src/collectd.conf.pod
index 3e43ca26..a06abe92 100644
--- a/src/collectd.conf.pod
+++ b/src/collectd.conf.pod
@@ -7632,7 +7632,7 @@ the timestamp as the score. Retrieving a date range can then be done using the
 C<ZRANGEBYSCORE> I<Redis> command. Additionally, all the identifiers of these
 I<Sorted Sets> are kept in a I<Set> called C<collectd/values> (or
 C<${prefix}/values> if the B<Prefix> option was specified) and can be retrieved
-using the C<SMEMBERS> I<Redis> command. You can specify the database to use 
+using the C<SMEMBERS> I<Redis> command. You can specify the database to use
 with the B<Database> parameter (default is C<0>). See
 L<http://redis.io/commands#sorted_set> and L<http://redis.io/commands#set> for
 details.
@@ -7677,7 +7677,13 @@ is recommended but not required to include a trailing slash in I<Prefix>.
 
 =item B<Database> I<Index>
 
-This index selects the redis database to use for writing operations. Defaults to C<0>.
+This index selects the redis database to use for writing operations. Defaults
+to C<0>.
+
+=item B<MaxSetSize> I<Items>
+
+The B<MaxSetSize> option limits the number of items that the I<Sorted Sets> can
+hold. Negative values for I<Items> sets no limit, which is the default behavior.
 
 =back
 
diff --git a/src/write_redis.c b/src/write_redis.c
index 5560b4d1..8dea10c8 100644
--- a/src/write_redis.c
+++ b/src/write_redis.c
@@ -46,6 +46,7 @@ struct wr_node_s
   struct timeval timeout;
   char *prefix;
   int database;
+  int max_set_size;
 
   redisContext *conn;
   pthread_mutex_t lock;
@@ -105,7 +106,7 @@ static int wr_write (const data_set_t *ds, /* {{{ */
       pthread_mutex_unlock (&node->lock);
       return (-1);
     }
-   
+
     rr = redisCommand(node->conn, "SELECT %d", node->database);
     if (rr == NULL)
       WARNING("SELECT command error. database:%d message:%s", node->database, node->conn->errstr);
@@ -119,6 +120,15 @@ static int wr_write (const data_set_t *ds, /* {{{ */
   else
     freeReplyObject (rr);
 
+  if (node->max_set_size >= 0)
+  {
+    rr = redisCommand (node->conn, "ZREMRANGEBYRANK %s %d %d", key, 0, (-1 * node->max_set_size) - 1);
+    if (rr == NULL)
+      WARNING("SELECT command error. database:%d message:%s", node->database, node->conn->errstr);
+    else
+      freeReplyObject (rr);
+  }
+
   /* TODO(octo): This is more overhead than necessary. Use the cache and
    * metadata to determine if it is a new metric and call SADD only once for
    * each metric. */
@@ -170,6 +180,7 @@ static int wr_config_node (oconfig_item_t *ci) /* {{{ */
   node->conn = NULL;
   node->prefix = NULL;
   node->database = 0;
+  node->max_set_size = -1;
   pthread_mutex_init (&node->lock, /* attr = */ NULL);
 
   status = cf_util_get_string_buffer (ci, node->name, sizeof (node->name));
@@ -204,6 +215,9 @@ static int wr_config_node (oconfig_item_t *ci) /* {{{ */
     else if (strcasecmp ("Database", child->key) == 0) {
       status = cf_util_get_int (child, &node->database);
     }
+    else if (strcasecmp ("MaxSetSize", child->key) == 0) {
+      status = cf_util_get_int (child, &node->max_set_size);
+    }
     else
       WARNING ("write_redis plugin: Ignoring unknown config option \"%s\".",
           child->key);
-- 
2.11.0