diff --git a/.env.example b/.env.example
index fb9fde2..6523c76 100644
--- a/.env.example
+++ b/.env.example
@@ -1,3 +1,4 @@
 SIGN_KEY=
 DEBUG=0
 MAIN_REDIRECT=https://github.com/shiftinv/github-webhook-filter
+REDIS_URL=
diff --git a/deps.ts b/deps.ts
index 103ebee..752a04b 100644
--- a/deps.ts
+++ b/deps.ts
@@ -1,4 +1,4 @@
 export * as http from "https://deno.land/std@0.154.0/http/mod.ts";
 export * as log from "https://deno.land/std@0.154.0/log/mod.ts";
 export * as hex from "https://deno.land/std@0.154.0/encoding/hex.ts";
-export { default as TTL } from "https://deno.land/x/ttl@1.0.1/mod.ts";
+export * as redis from "https://deno.land/x/redis@v0.27.0/mod.ts";
diff --git a/lib/config.ts b/lib/config.ts
index 7749b2a..445f508 100644
--- a/lib/config.ts
+++ b/lib/config.ts
@@ -17,6 +17,7 @@ export default {
     maxWebhookRetries: parseInt(get("MAX_RETRIES", "3")),
     maxWebhookRetryMs: parseInt(get("MAX_RETRY_MS", "30000")),
     mainRedirect: get("MAIN_REDIRECT", null),
+    redisUrl: get("REDIS_URL"),
 
     // set by deno deploy
     deployId: get("DENO_DEPLOYMENT_ID", "<unknown>"),
diff --git a/lib/filter.ts b/lib/filter.ts
index 1779cbc..753b25c 100644
--- a/lib/filter.ts
+++ b/lib/filter.ts
@@ -1,10 +1,12 @@
-import { TTL } from "../deps.ts";
+import { reviewCommentManager } from "./manager.ts";
 import { UrlConfig } from "./types.d.ts";
 import { requestLog } from "./util.ts";
 
-const reviewComments = new TTL<number>(2 * 1000);
-
-export default function filter(headers: Headers, json: any, config: UrlConfig): string | null {
+export default async function filter(
+    headers: Headers,
+    json: any,
+    config: UrlConfig,
+): Promise<string | null> {
     const reqLog = requestLog(headers);
     const event = headers.get("x-github-event") || "unknown";
     const login: string | undefined = json.sender?.login?.toLowerCase();
@@ -47,14 +49,11 @@ export default function filter(headers: Headers, json: any, config: UrlConfig):
         if (config.commentBurstLimit && reviewId) {
             const cacheKey = `${reviewId}-${login}`;
             reqLog.debug(`filter: checking cache key ${cacheKey}`);
-            reqLog.debug(
-                `filter: full comment cache ${JSON.stringify(Array.from(reviewComments))}`,
-            );
-            const curr = reviewComments.get(cacheKey);
+            const curr = await reviewCommentManager.getAndIncrement(cacheKey);
+            reqLog.debug(`filter: current value: ${curr}`);
             if (curr && curr >= config.commentBurstLimit) {
                 return `exceeded comment burst limit (${config.commentBurstLimit}) for review ${reviewId}`;
             }
-            reviewComments.set(cacheKey, (curr ?? 0) + 1);
         }
     }
 
diff --git a/lib/handler.ts b/lib/handler.ts
index f8a773f..cbf27d2 100644
--- a/lib/handler.ts
+++ b/lib/handler.ts
@@ -40,7 +40,7 @@ export default async function handle(
     const json = JSON.parse(data);
 
     // do the thing
-    const filterReason = filterWebhook(req.headers, json, urlConfig);
+    const filterReason = await filterWebhook(req.headers, json, urlConfig);
     if (filterReason !== null) {
         const reqLog = requestLog(req.headers);
         reqLog.debug(`handler: ignored due to '${filterReason}'`);
diff --git a/lib/manager.ts b/lib/manager.ts
new file mode 100644
index 0000000..78fce32
--- /dev/null
+++ b/lib/manager.ts
@@ -0,0 +1,28 @@
+import { redis } from "../deps.ts";
+import config from "./config.ts";
+
+class ReviewCommentManager {
+    private redis: redis.Redis;
+    constructor() {
+        this.redis = redis.createLazyClient({
+            ...redis.parseURL(config.redisUrl),
+            maxRetryCount: 3,
+        });
+    }
+
+    async getAndIncrement(key: string): Promise<number> {
+        if (!this.redis.isConnected) {
+            // seems like pipelines don't quite work with the lazy client
+            await this.redis.ping();
+        }
+        const pl = this.redis.pipeline();
+        pl.incr(`reviewcomment:${key}`);
+        pl.expire(`reviewcomment:${key}`, 3);
+        const results = await pl.flush();
+
+        const newValue = results[0] as number;
+        return newValue - 1; // return old value
+    }
+}
+
+export const reviewCommentManager = new ReviewCommentManager();