dbmapper | Simple asynchronous Scala database access , data mapper | Database library

It's a Java lambda and it's taking 4s to perform each of 2 DynamoDB operations, using the AWS-supplied SDK. I've heard that these typically complete within <20ms, but for me it's 3 orders of magnitude higher. These long operations are (a) creating the DynamoDB object and (b) performing a table scan on a completely empty table (code below).

What should I do to reduce the latency?

• Both the lambda and DynamoDB are in the same region (eu-west-1).
• The table has 5 RCU & WCU. Increasing these doesn't help.
• The maximum memory used by the lambda is 92MB. If I allocate the minimum 128MB then it times out after 15s. Increasing the memory to 512MB achieves the timings of 4s per call and increasing it again to 1GB reduces it to 2s per call. However, this is an absurd amount of memory for a trivial lambda and still leaves me with >200x the expected latency.
• Table metrics show the table scan time is between 12ms and 15ms. This is what I was expecting. Even with the overhead of establishing a network connection, I'm still expecting a few 10s of milliseconds, not several seconds.
• I'm triggering the lambda using the test function in the AWS console. I've also tried triggering via API Gateway (which is what I'll be doing eventually) with the same results.
• I've tried calling the lambda several times in quick succession (to reduce the likelihood that I'm suffering setup costs). It didn't help.
• Logging shows all other parts of the lambda running very quickly (milliseconds).

Creating the DynamoDB objects

I want to get an API request and save request's data to a DB. Also want to return the data (that is written to DB). I know, this is possible in RxJava, but now I write in Kotlin coroutines, currently use Fuel instead of Retrofit (but a difference is not so large). I read How to use Fuel with a Kotlin coroutine, but don't understand it.

How to write a coroutine and methods?

UPDATE

Say, we have a Java and Retrofit, RxJava. Then we can write a code.

RegionResponse:

I am creating a REST service using springboot and DynamoDB as database. I have a StudentDTO class with the following fields and Subject class which has subjects info as (key,value pair) :

I have a User entity with an id

I want to update a table in Postgres using ibatis dbmapper.xml.

Condition is it should update only those columns for which the map contains values. For other columns the value should not be touched.

Say I have a Company Table with following columns {company_id, name, headQrtr, ceo}

If i want to update any particular row in Company table using company_id, I will be having following code snippet(dbmapper.xml)