add partition counter based on stream shards

bin/dynamodb-partition-count.js

@@ -0,0 +1,10 @@
+#!/usr/bin/env node
+
+var region = process.argv[2].split('/')[0];
+var table = process.argv[2].split('/')[1];
+var throughput = require('..')(table, { region: region });
+
+throughput.partitionCount(function(err, partitionCount) {
+  if (err) throw err;
+  console.log('Found %s partitions', partitionCount);
+});

index.js

@@ -1,4 +1,5 @@
 var AWS = require('aws-sdk');
+var async = require('queue-async');
 
 module.exports = function(tableName, dynamoOptions) {
   var cache = {
@@ -66,6 +67,46 @@ module.exports = function(tableName, dynamoOptions) {
     });
   }
 
+  function describePartitions(callback) {
+    var streams = new AWS.DynamoDBStreams({ region: dynamoOptions.region });
+    streams.listStreams({ TableName: tableName }, function(err, data) {
+      if (err) return callback(err);
+      if (!data.Streams[0]) return callback(new Error('Must enable DynamoDB Streams to count partitions'));
+
+      var arn = data.Streams[0].StreamArn;
+      streams.describeStream({ StreamArn: arn }, function(err, data) {
+        if (err) return callback(err);
+
+        var shards = data.StreamDescription.Shards;
+        var queue = async();
+
+        shards.forEach(function(shard) {
+          queue.defer(function(next) {
+            streams.getShardIterator({
+              ShardId: shard.ShardId,
+              ShardIteratorType: 'LATEST',
+              StreamArn: arn
+            }, function(err, data) {
+              if (err) return next(err);
+
+              streams.getRecords({
+                ShardIterator: data.ShardIterator
+              }, function(err, data) {
+                if (err) return next(err);
+                next(null, data.Records.length || 'NextShardIterator' in data ? 1 : 0);
+              });
+            });
+          });
+        });
+
+        queue.awaitAll(function(err, results) {
+          if (err) return callback(err);
+          callback(null, results.reduce(function(count, num) { count += num; return count; }, 0));
+        });
+      });
+    });
+  }
+
   var throughput = {
     tableInfo: function(callback) {
       describeTable(function(err, main, indexes) {
@@ -117,6 +158,8 @@ module.exports = function(tableName, dynamoOptions) {
       });
     },
 
+    partitionCount: describePartitions,
+
     setCapacity: function(capacity, callback) {
       if (cache.main.read && cache.main.write) return update();
 

package.json

@@ -9,7 +9,8 @@
   },
   "bin": {
     "dynamodb-throughput-info": "bin/dynamodb-throughput-info.js",
-    "dynamodb-throughput-adjustment": "bin/dynamodb-throughput-adjustment.js"
+    "dynamodb-throughput-adjustment": "bin/dynamodb-throughput-adjustment.js",
+    "dynamodb-partition-count": "bin/dynamodb-partition-count.js"
   },
   "repository": {
     "type": "git",
@@ -23,8 +24,9 @@
   "author": "Mapbox",
   "license": "ISC",
   "dependencies": {
-    "aws-sdk": "^2.1.17",
-    "minimist": "^1.1.1"
+    "aws-sdk": "^2.1.46",
+    "minimist": "^1.1.1",
+    "queue-async": "^1.0.7"
   },
   "devDependencies": {
     "dynalite": "^0.12.0",