Read/write in the same table - spring-batch

Question

I have a chunk tasklet in Spring Batch. The processor reads form table A, the writer writes to table A when the record is not present. When I configure the commit-interval to 1, it works fine.
When i configure the commit-interval to a higher number i'm getting dublicate entry execptions because the processor didn't get the dirty read information.
My Tasklet is configured with a read uncommit statement:
batch:transaction-attributes isolation = "READ_UNCOMMITTED"
I think that this configurations was not accepted in my configuration? Any ideas?

Answer 1

You shouldn't encountered this problem because read/process/write are (usually) managed in this manner:
read is done in a separate connection
chunk write is done in its own transaction for skip/retry/fault management
You don't need to use READ_UNCOMMITTED but more easy:
Create a ItemReader<S> (a JdbcCursorItemReader should be fine)
Process your item with an ItemProcessor<S,T>
Write your own ItemWriter<T> that write/update an object based on its presence on database
If you want to reduce items to write with your custom writer you can filter out duplicate objects during process phase: you can achive this goal using a map to store duplicated items like described by #jackson (only for current chunk items, not for all rows in database - this step is done later by ItemWriter)

Answer 2

dirty reads in general is a scary idea.
sounds like it is a design issue instead.
what you should be doing is...
1) sounds like you should introduce a cache/map to store entries you plan to commit, but haven't written into db yet.
if the entry is already in table A or in the cache, skip.
if the entry is NOT in table A or the cache, then save a copy into the cache, and add it to the list of candidates to be written by the writer.