Healing Party (Batch Operations)

What you'll learn

Batch operations process multiple items in a single network request.
BatchGetItem accepts up to 100 keys and returns at most 16 MB per request; partial results can also occur above 1 MB per partition.
Responses are unordered and may contain UnprocessedKeys that must be retried.

Section 01

Healing the Party (BatchGetItem)

By passing an array of keys to BatchGetItem, we reduce network round trips. A successful HTTP response can still be partial, so merge responses by key and retry UnprocessedKeys with exponential backoff and jitter.

BatchGetItemJavaScript

import { DynamoDBClient } from "@aws-sdk/client-dynamodb";
import { DynamoDBDocumentClient, BatchGetCommand } from "@aws-sdk/lib-dynamodb";

const client = new DynamoDBClient({ region: "ap-south-1" });
const docClient = DynamoDBDocumentClient.from(client);

// Re-send any UnprocessedKeys with backoff (see the lab below).
const { Responses, UnprocessedKeys } = await docClient.send(new BatchGetCommand({
  RequestItems: {
    "JohtoPokemon": {
      Keys: [
        { Name: "Chikorita" },
        { Name: "Cyndaquil" },
        { Name: "Totodile" }
      ]
    }
  }
}));

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All steps as text

Your app sends BatchGetItem to the JohtoPokemon table with Name = "Chikorita, Cyndaquil, Totodile".
DynamoDB hashes "Chikorita" to df9e8fa1, which routes the request to partition P1.
DynamoDB hashes "Cyndaquil" to 6203cc87, which routes the request to partition P3.
DynamoDB hashes "Totodile" to e49e153a, which routes the request to partition P2.
P1 returns Chikorita.
P3 returns Cyndaquil.
DynamoDB responds with success: 2 of 3 returned. Totodile sat in UnprocessedKeys and was never retried.

Practice

Your turn

Load the party efficiently. Finish the Keys array and keep retrying UnprocessedKeys, because batch responses can be partial and their item order is not guaranteed.

Add Cyndaquil and Totodile. The starter loop already re-sends response.UnprocessedKeys with capped exponential backoff and jitter, so keep it.

// @ts-nocheck
import { DynamoDBClient } from "@aws-sdk/client-dynamodb";
import { DynamoDBDocumentClient, BatchGetCommand } from "@aws-sdk/lib-dynamodb";
const client = new DynamoDBClient({ region: "ap-south-1" });
const docClient = DynamoDBDocumentClient.from(client);
async function healParty() {
  /** @type {import("@aws-sdk/lib-dynamodb").BatchGetCommandInput["RequestItems"]} */
  let requestItems = {
      JohtoPokemon: {
        Keys: [
          { Name: "Chikorita" },
          // ⬇️ Add the other two starters so all three heal in one request.
        ],
      },
  };
  // BatchGet can return partial results. Keep retrying UnprocessedKeys.
  const party = [];
  let attempts = 0;
  do {
    const response = await docClient.send(new BatchGetCommand({ RequestItems: requestItems }));
    party.push(...(response.Responses?.JohtoPokemon ?? []));
    requestItems = response.UnprocessedKeys ?? {};
    if (Object.keys(requestItems).length > 0) {
      if (++attempts >= 6) throw new Error("Retry budget exhausted; preserve remaining keys for later.");
      const delay = Math.random() * Math.min(2000, 100 * 2 ** attempts);
      await new Promise(resolve => setTimeout(resolve, delay));
    }
  } while (Object.keys(requestItems).length > 0);
  console.log("Loaded party (response order is not guaranteed):", party);
}

// @ts-nocheck
import { DynamoDBClient } from "@aws-sdk/client-dynamodb";
import { DynamoDBDocumentClient, BatchGetCommand } from "@aws-sdk/lib-dynamodb";

const client = new DynamoDBClient({ region: "ap-south-1" });
const docClient = DynamoDBDocumentClient.from(client);

async function healParty() {
  /** @type {import("@aws-sdk/lib-dynamodb").BatchGetCommandInput["RequestItems"]} */
  let requestItems = {
      JohtoPokemon: {
        Keys: [
          { Name: "Chikorita" },
          // ⬇️ Add the other two starters so all three heal in one request.

        ],
      },
  };

  // BatchGet can return partial results. Keep retrying UnprocessedKeys.
  const party = [];
  let attempts = 0;
  do {
    const response = await docClient.send(new BatchGetCommand({ RequestItems: requestItems }));
    party.push(...(response.Responses?.JohtoPokemon ?? []));
    requestItems = response.UnprocessedKeys ?? {};
    if (Object.keys(requestItems).length > 0) {
      if (++attempts >= 6) throw new Error("Retry budget exhausted; preserve remaining keys for later.");
      const delay = Math.random() * Math.min(2000, 100 * 2 ** attempts);
      await new Promise(resolve => setTimeout(resolve, delay));
    }
  } while (Object.keys(requestItems).length > 0);

  console.log("Loaded party (response order is not guaranteed):", party);
}

Ctrl/⌘ Enter to run · simulated, no AWS callsSimulated — no AWS calls

Check

Check your understanding

Quick Quiz · one question, as many tries as you need.

What is the maximum number of items you can retrieve in a single BatchGetItem request?

Choose one answer.