Tweaks to how doatasource manageers cache connections

diff --git a/src/library/LRUCache.php b/src/library/LRUCache.php
index bc0077556..10a42c281 100644
--- a/src/library/LRUCache.php
+++ b/src/library/LRUCache.php
@@ -49,12 +49,17 @@ class LRUCache
      * @var int
      */
     private $size;
+    /**
+     * Default size of LRU Cache
+     * @var int
+     */
+    const DEFAULT_SIZE = 200;
     /**
      * Creates an empty cache and sets the size
      *
      * @param int $size size of the cache
      */
-    public function __construct($size = 100)
+    public function __construct($size = self::DEFAULT_SIZE)
     {
         $this->cache = [];
         $this->size = $size;
@@ -107,4 +112,4 @@ class LRUCache
     {
         return $this->cache;
     }
-}
\ No newline at end of file
+}
diff --git a/src/library/media_jobs/RecommendationJob.php b/src/library/media_jobs/RecommendationJob.php
index 1ebd33070..4c060f141 100644
--- a/src/library/media_jobs/RecommendationJob.php
+++ b/src/library/media_jobs/RecommendationJob.php
@@ -947,7 +947,7 @@ class RecommendationJob extends MediaJob
                 $this->lru_cache->put($row['ID'],
                     base64_decode($row['VECTOR'], true));
             } else {
-                var_dump($row['VECTOR']);
+                var_dump($row);
             }
         }
         $context_distance_sum = (self::CONTEXT_WINDOW_LENGTH *
diff --git a/src/models/datasources/MysqlManager.php b/src/models/datasources/MysqlManager.php
index e34eedfcb..ab03e5493 100755
--- a/src/models/datasources/MysqlManager.php
+++ b/src/models/datasources/MysqlManager.php
@@ -93,7 +93,6 @@ class MysqlManager extends PdoManager
                 $this->pdo = new \PDO("mysql:host={$db_host}".
                     $db_port_string . $db_name_string,
                     $db_user, $db_password);
-                self::$active_connections[$this->connect_string] = $this->pdo;
             } catch (\PDOException $e) {
                 $this->pdo = false;
                 L\crawlLog("MysqlManager.php Connection failed: \n" .
@@ -104,6 +103,7 @@ class MysqlManager extends PdoManager
         } else {
             $this->pdo = self::$active_connections[$this->connect_string];
         }
+        $this->updateConnectionCache();
         $this->to_upper_dbms = "MYSQL";
         return $this->pdo;
     }
diff --git a/src/models/datasources/PdoManager.php b/src/models/datasources/PdoManager.php
index daf3d7aa3..4152ca4b5 100644
--- a/src/models/datasources/PdoManager.php
+++ b/src/models/datasources/PdoManager.php
@@ -99,6 +99,11 @@ class PdoManager extends DatasourceManager
      * @var array
      */
     public static $active_connections = [];
+    /**
+     * Maximum number of connections to cache
+     * @var int
+     */
+    const MAX_CONNECTIONS = 20;
     /**
      * {@inheritDoc}
      *
@@ -125,7 +130,6 @@ class PdoManager extends DatasourceManager
             try {
                 $this->pdo = new \PDO($db_host, $db_user, $db_password,
                     [\PDO::ATTR_ERRMODE => \PDO::ERRMODE_EXCEPTION]);
-                self::$active_connections[$this->connect_string] = $this->pdo;
             } catch (\PDOException $e) {
                 $this->pdo = false;
                 L\crawlLog("PDOManager.php Connection failed: \n" .
@@ -135,12 +139,27 @@ class PdoManager extends DatasourceManager
         } else {
             $this->pdo = self::$active_connections[$this->connect_string];
         }
+        $this->updateConnectionCache();
         $this->to_upper_dbms = false;
         if (stristr($db_host, 'PGSQL')) {
             $this->to_upper_dbms = 'PGSQL';
         }
         return $this->pdo;
     }
+    /**
+     * Caches current PDO connection. If cache full evicts last
+     */
+    public function updateConnectionCache()
+    {
+        unset(self::$active_connections[$this->connect_string]);
+        self::$active_connections = [$this->connect_string => $this->pdo] +
+            self::$active_connections;
+        if (count(self::$active_connections) >= self::MAX_CONNECTIONS) {
+            $oldest_connection = array_key_last(self::$active_connections);
+            L\crawlLog("Evicting old db connection: $oldest_connection");
+            unset(self::$active_connections[$oldest_connection]);
+        }
+    }
     /** {@inheritDoc} */
     public function disconnect()
     {
diff --git a/src/models/datasources/Sqlite3Manager.php b/src/models/datasources/Sqlite3Manager.php
index c94237b11..cae3eafad 100644
--- a/src/models/datasources/Sqlite3Manager.php
+++ b/src/models/datasources/Sqlite3Manager.php
@@ -86,12 +86,11 @@ class Sqlite3Manager extends PdoManager
         $this->connect_time = time();
         $this->connect_string = "$db_host:$db_user:$db_password:$db_name";
         if (empty(self::$active_connections[$this->connect_string])) {
-            self::$active_connections[$this->connect_string] =
-                new \PDO($connect);
-        }
-        if (empty($this->pdo)) {
+            $this->pdo = new \PDO($connect);
+        } else {
             $this->pdo = self::$active_connections[$this->connect_string];
         }
+        $this->updateConnectionCache();
         $this->to_upper_dbms = "SQLITE3";
         return $this->pdo;
     }