Amnon Heiman 08c81427b9 Add paging for internal queries ...

Usually, internal queries are used for short queries. Sometimes though,
like in the case of get compaction history, there could be a large
amount of results. Without paging it will overload the system.

This patch adds the ability to use paging internally.

Using paging will be done explicitely, all the relevant information
would be store in an internal_query_state, that would hold both the
paging state but also the query so consecutive calls can be made.

To use paging use the query method with a function.

The function gets beside a statement and its parameters a function that
will be used for each of the returned rows.

For example if qp is a query_processor:

qp.query("SELECT * from system.compaction_history", [] (const cql3::untyped_result_set::row& row) {
  ....
  // do something with row
  ...
  return stop_iteration::no; // keep on reading
});

Will run the function on each of the compaction history table rows.

To stop the iteration, the function can return stop_iteration::yes.

2017-07-20 17:43:51 +03:00

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