How to get the data/value size in Redis keys with prefix?

Question

I stored a lot of stuff in Redis. One group of them are with namespace cache (key starts with cache:). I want to know the size of the data/values with namespace cache. Can I achieve this in Redis? Any suggestions?

Answer 1

nodejs snippet using ioredis:

const Redis = require("ioredis");
let redisClient = new Redis({
  port: 6379, // Redis port
  host: "127.0.0.1", // Redis host
  username: "default", // needs Redis >= 6
  password: "my-top-secret",
  db: 0, // Defaults to 0
});
async function calculateKeysSize(redisClient, matchPattern) {
  let iterations = 0;
  let totalKeys = 0;
  let totalBytes = 0;
  let nextCursor, currCursorKeys;
  while (nextCursor !== "0") {
    [nextCursor, currCursorKeys] = await redisClient.scan(nextCursor || 0, "match", matchPattern);

    totalKeys += currCursorKeys.length;

    const pipeline = redisClient.pipeline();
    for (const currKey of currCursorKeys) {
      pipeline.memory("usage", currKey);
    }
    const responses = await pipeline.exec();
    const sizes = responses.map((response) => response[1]);
    totalBytes += sizes.reduce((a, b) => a + b, 0);

    if (iterations % 1000 == 0) {
      console.log(`scanned ${totalKeys} so far.. total size: ${totalBytes} Bytes`);
    }
    iterations++;
  }

  return { totalKeys, totalBytes };
}

await calculateKeysSize(redisClient, "cache:*");

gist link for ready-to-use script.

Answer 2

You can do this with RedisGears (https://oss.redislabs.com/redisgears/) with a single line:

RG.PYEXECUTE "GB().map(lambda x: int(execute('MEMORY', 'USAGE', x['key']))).aggregate(0, lambda a,x: a+x, lambda a,x: a+x).run('cache:*')"

The first map operation get the size of each key and the aggregate operation sums it. the argument to the run function is the keys prefix to run on.