Is it possible to query all records in Cassandra based on a condition?

Question

I have a table with contains a list of user records. I need to query all records based on some condition. The use case is I have about 30 million records in the user table and my condition would match 3 million.

I have gone thru https://www.datastax.com/dev/blog/a-deep-look-to-the-cql-where-clause however, I couldn't find any real solution.

Is it even possible to query Cassandra table based on a condition?

I need to query and paginate the records just like a tradional rdbms or document store.

Answer 1

Cassandra has a concept of paging where you can specify the fetch size and then iterate over it page by page. The below code is if you are using Datastax Java Driver to query data. But other language should also have something similar.

final int RESULTS_PER_PAGE = 100;

Statement st = new SimpleStatement("your query");
st.setFetchSize(RESULTS_PER_PAGE);

String requestedPage = extractPagingStateStringFromURL();
// This will be absent for the first page
if (requestedPage != null) {
    st.setPagingState(
        PagingState.fromString(requestedPage));
}

ResultSet rs = session.execute(st);
PagingState nextPage = rs.getExecutionInfo().getPagingState();

// Note that we don't rely on RESULTS_PER_PAGE, since Cassandra might
// have not respected it, or we might be at the end of the result set
int remaining = rs.getAvailableWithoutFetching();
for (Row row : rs) {
    renderInResponse(row);
    if (--remaining == 0) {
        break;
    }
}

// This will be null if there are no more pages
if (nextPage != null) {
    renderNextPageLink(nextPage.toString());
}

More details can be found here .