bmatheny · March 14, 2013 19:06 · Mar 14, 2013
diff --git a/DuplicateRequestFilter.scala b/DuplicateRequestFilter.scala
@@ -0,0 +1,47 @@
+package com.tumblr.fibr.service.filter
+
+import com.tumblr.fibr.config.FilterConfig
+import com.tumblr.fibr.tsdb.{TsdbRequest, TsdbResponse}
+import com.google.common.cache.{Cache, CacheBuilder}
+import com.twitter.finagle.Service
+import com.twitter.util.Future
+import java.util.concurrent.{Callable, TimeUnit}
+
+/**
+ * If we see the same request within timeoutInSeconds, return the same response
+ */
+class DuplicateRequestFilter(override val filterConfig: FilterConfig,
+                             timeoutInSeconds: Int = 300)
+  extends ServiceFilter
+{
+  type TsdbService = Service[TsdbRequest, TsdbResponse]
+  val NotFoundInCache = mkStatName("query", "cache", "miss")
+  val FoundInCache = mkStatName("query", "cache", "hit")
+  val RequestedFromCache = mkStatName("query", "cache", "request")
+
+  private[this] val cache: Cache[TsdbRequest,Future[TsdbResponse]] = CacheBuilder.newBuilder()
+      .maximumSize(500)
+      .expireAfterAccess(timeoutInSeconds, TimeUnit.SECONDS)
+      .build()
+
+  override def apply(request: TsdbRequest, service: TsdbService): Future[TsdbResponse] = {
+    val wasPresent = cache.getIfPresent(request)
+    cache.get(request, new Callable[Future[TsdbResponse]] {
+      override def call: Future[TsdbResponse] = {
+        service(request)
+      }
+    }).ensure {
+      wasPresent match {
+        case null =>
+          Stats.incr(NotFoundInCache)
+        case o =>
+          Stats.incr(FoundInCache)
+          log.info("Found query in cache: %s".format(request.toString))
+      }
+      Stats.incr(RequestedFromCache)
+    }
+  }
+
+  val EvictedFromCache = mkStatName("query", "cache", "evict")
+  Stats.addGauge(EvictedFromCache) { cache.stats.evictionCount }
+}