Not able to solve throttlingException in DynamoDB

问题

I have a lambda function which does a transaction in DynamoDB similar to this.

try {
        const reservationId = genId();
        await transactionFn();
        return {
            statusCode: 200,
            body: JSON.stringify({id: reservationId})
        };

        async function transactionFn() {
            try {
                await docClient.transactWrite({
                    TransactItems: [
                        {
                            Put: {
                                TableName: ReservationTable,
                                Item: {
                                    reservationId,
                                    userId,
                                    retryCount: Number(retryCount),
                                }
                            }
                        },
                        {
                            Update: {
                                TableName: EventDetailsTable,
                                Key: {eventId},
                                ConditionExpression: 'available >= :minValue',
                                UpdateExpression: `set available = available - :val, attendees= attendees + :val, lastUpdatedDate = :updatedAt`,
                                ExpressionAttributeValues: {
                                    ":val": 1,
                                    ":updatedAt": currentTime,
                                    ":minValue": 1
                                }
                            }
                        }
                    ]

                }).promise();
                return true
            } catch (e) {
                const transactionConflictError = e.message.search("TransactionConflict") !== -1;
                // const throttlingException = e.code === 'ThrottlingException';
                console.log("transactionFn:transactionConflictError:", transactionConflictError);
                if (transactionConflictError) {
                    retryCount += 1;
                    await transactionFn();
                    return;
                }
                // if(throttlingException){
                //
                // }
                console.log("transactionFn:e.code:", JSON.stringify(e));
                throw e
            }
        }

It just updating 2 tables on api call. If it encounter a transaction conflict error, it simply retry the transaction by recursively calling the function.

The eventDetails table is getting too much db updates. ( checked it with aws Contributor Insights) so, made provisioned unit to a higher value than earlier.

For reservationTable Provisioned capacity is on Demand.

When I do load test over this api with 400 (or more) users using JMeter (master slave configuration) I am getting Throttled error for some api calls and some api took more than 20 sec to respond. When I checked X-Ray for this api found that, DynamoDB is taking too much time for this transasction for the slower api calls.

Even with much fixed provisioning ( I tried on demand scaling too ) , I am getting throttled exception for api calls.

ProvisionedThroughputExceededException: The level of configured provisioned throughput for the table was exceeded.
Consider increasing your provisioning level with the UpdateTable API.

UPDATE

And one more thing. When I do the load testing, I am always uses the same eventId. It means, I am always updating the same row for all the api requests. I have found this article, which says that, a single partition can only have upto 1000 WCU. Since I am always updating the same row in the eventDetails table during load testing, is that causing this issue ?

回答1:

I had this exact error and it helped me to change the On Demand to Provisioned under Read/write capacity mode. Try to change that, if that doesn't help, we'll go from there.

来源：https://stackoverflow.com/questions/59929823/not-able-to-solve-throttlingexception-in-dynamodb