What is the recommended way to delete a large number of items from DynamoDB

Question

I m writing a simple logging service in DynamoDB   I have a logs table that is keyed by a user id hash and a timestamp  Unix epoch int  range   When a user of the service terminates their account  I need to delete all items in the table  regardless of the range value   What is the recommended way of doing this sort of operation  Keeping in mind there could be millions of items to delete    My options  as far as I can see are   A  Perform a Scan operation  calling delete on each returned item  until no items are left  B  Perform a BatchGet operation  again calling delete on each item until none are left  Both of these look terrible to me as they will take a long time   What I ideally want to do is call LogTable DeleteItem user id  - Without supplying the range  and have it delete everything for me

User · Answer

If you want to delete items after some time, e.g. after a month, just use Time To Live option. It will not count write units.

In your case, I would add ttl when logs expire and leave those after a user is deleted. TTL would make sure logs are removed eventually.

When Time To Live is enabled on a table, a background job checks the TTL attribute of items to see if they are expired.

DynamoDB typically deletes expired items within 48 hours of expiration. The exact duration within which an item truly gets deleted after expiration is specific to the nature of the workload and the size of the table. Items that have expired and not been deleted will still show up in reads, queries, and scans. These items can still be updated and successful updates to change or remove the expiration attribute will be honored.

https://docs.aws.amazon.com/amazondynamodb/latest/developerguide/TTL.html https://docs.aws.amazon.com/amazondynamodb/latest/developerguide/howitworks-ttl.html

User · Answer

The answer of this question depends on the number of items and their size  and your budget  Depends on that we have following 3 cases   1- The number of items and size of items in the table are not very much  then as Steffen Opel said you can Use Query rather than Scan to retrieve all items for user id and then loop over all returned items and either facilitate DeleteItem or BatchWriteItem  But keep in mind you may burn a lot of throughput capacity here  For example  consider a situation where you need delete 1000 items from a DynamoDB table  Assume that each item is 1 KB in size  resulting in Around 1MB of data  This bulk-deleting task will require a total of 2000 write capacity units for query and delete  To perform this data load within 10 seconds  which is not even considered as fast in some applications   you would need to set the provisioned write throughput of the table to 200 write capacity units  As you can see its doable to use this way if its for less number of items or small size items   2- We have a lot of items or very large items in the table and we can store them according to the time into different tables  Then as  jonathan Said you can just delete the table  this is much better but I don t think it is matched with your case  As you want to delete all of users data no matter what is the time of creation of logs  so in this case you can t delete a particular table  if you wanna have a separate table for each user then I guess if number of users are high then its so expensive and it is not practical for your case   3- If you have a lot of data and you can t divide your hot and cold data into different tables and you need to do large scale delete frequently then unfortunately DynamoDB is not a good option for you at all  It may become more expensive or very slow depends on your budget   In these cases I recommend to find another database for your data

User · Answer

Thought about using the test to pass in the vars  Something like  Test input would be something like       quot TABLE NAME quot    quot MyDevTable quot      quot PARTITION KEY quot    quot REGION quot      quot SORT KEY quot    quot COUNTRY quot     Adjusted your code to accept the inputs  const AWS   require  aws-sdk    const docClient   new AWS DynamoDB DocumentClient   apiVersion   2012-08-10       exports handler   async  event    gt        const TABLE NAME   event TABLE NAME      const PARTITION KEY   event PARTITION KEY      const SORT KEY   event SORT KEY      let params             TableName  TABLE NAME             console log  keys    PARTITION KEY    SORT KEY          let items           let data   await docClient scan params  promise        items       items     data Items            while  typeof data LastEvaluatedKey     undefined             params ExclusiveStartKey   data LastEvaluatedKey           data   await docClient scan params  promise            items       items     data Items              let leftItems   items length      let group           let groupNumber   0       console log  Total items to be deleted   leftItems        for  const i of items               console log  item    i PARTITION KEY      i SORT KEY              const deleteReq    DeleteRequest   Key                  deleteReq DeleteRequest Key PARTITION KEY    i PARTITION KEY           deleteReq DeleteRequest Key SORT KEY    i SORT KEY               console log  DeleteRequest    JSON stringify deleteReq              group push deleteReq           leftItems--           if  group length     25    leftItems  lt  1                groupNumber                 console log  Batch   groupNumber  to be deleted                  const params                     RequestItems                         TABLE NAME   group                                                 await docClient batchWrite params  promise                 console log                   Batch   groupNumber  processed  Left items    leftItems                                  reset             group                            const response             statusCode  200              Uncomment below to enable CORS requests         headers                 quot Access-Control-Allow-Origin quot    quot   quot                     body  JSON stringify  Hello from Lambda                return response

User · Answer

According to the DynamoDB documentation you could just delete the full table   See below    Deleting an entire table is significantly more efficient than removing items one-by-one  which essentially doubles the write throughput as you do as many delete operations as put operations   If you wish to delete only a subset of your data  then you could make separate tables for each month  year or similar  This way you could remove  last month  and keep the rest of your data intact   This is how you delete a table in Java using the AWS SDK   DeleteTableRequest deleteTableRequest   new DeleteTableRequest      withTableName tableName   DeleteTableResult result   client deleteTable deleteTableRequest

User · Answer

We don t have option to truncate dynamo tables  we have to drop the table and create again   DynamoDB Charges are based on ReadCapacityUnits  amp  WriteCapacityUnits   If we delete all items using BatchWriteItem function  it will use WriteCapacityUnits So better to delete specific records or delete the table and start again

User · Answer

My approach to delete all rows from a table i DynamoDb is just to pull all rows out from the table  using DynamoDbs ScanAsync and then feed the result list to DynamoDbs AddDeleteItems  Below code in C  works fine for me          public async Task DeleteAllReadModelEntitiesInTable                 List lt ReadModelEntity gt  readModels           var conditions   new List lt ScanCondition gt             readModels   await  context ScanAsync lt ReadModelEntity gt  conditions  GetRemainingAsync             var batchWork    context CreateBatchWrite lt ReadModelEntity gt             batchWork AddDeleteItems readModels           await batchWork ExecuteAsync           Note  Deleting the table and then recreating it again from the web console may cause problems if using YAML CloudFormation to create the table

User · Answer

What I ideally want to do is call LogTable DeleteItem user id  -   Without supplying the range  and have it delete everything for me    An understandable request indeed  I can imagine advanced operations like these might get added over time by the AWS team  they have a history of starting with a limited feature set first and evaluate extensions based on customer feedback   but here is what you should do to avoid the cost of a full scan at least    Use Query rather than Scan to retrieve all items for user id - this works regardless of the combined hash range primary key in use  because HashKeyValue and RangeKeyCondition are separate parameters in this API and the former only targets the Attribute value of the hash component of the composite primary key     Please note that you  ll have to deal with the query API paging here as usual  see the ExclusiveStartKey parameter      Primary key of the item from which to continue an earlier query  An   earlier query might provide this value as the LastEvaluatedKey if that   query operation was interrupted before completing the query  either   because of the result set size or the Limit parameter  The   LastEvaluatedKey can be passed back in a new query request to continue   the operation from that point    Loop over all returned items and either facilitate DeleteItem as usual   Update  Most likely BatchWriteItem is more appropriate for a use case like this  see below for details        Update  As highlighted by ivant  the BatchWriteItem operation enables you to put or delete several items across multiple tables in a single API call  emphasis mine       To upload one item  you can use the PutItem API and to delete one   item  you can use the DeleteItem API  However  when you want to upload   or delete large amounts of data  such as uploading large amounts of   data from Amazon Elastic MapReduce  EMR  or migrate data from another   database in to Amazon DynamoDB  this API offers an efficient   alternative    Please note that this still has some relevant limitations  most notably    Maximum operations in a single request     You can specify a total of up to 25 put or delete operations  however  the total request size cannot exceed 1 MB  the HTTP payload   Not an atomic operation     Individual operations specified in a BatchWriteItem are atomic  however BatchWriteItem as a whole is a  best-effort  operation and not an atomic operation  That is  in a BatchWriteItem request  some operations might succeed and others might fail          Nevertheless this obviously offers a potentially significant gain for use cases like the one at hand

[database] What is the recommended way to delete a large number of items from DynamoDB?

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