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package io.datakernel.crdt;
import io.datakernel.crdt.primitives.CrdtType;
import org.jetbrains.annotations.Nullable;
public interface CrdtFunction {
/**
* This method should combine two given CRDT values together,
* not violating any of the CRDT conditions.
*/
S merge(S first, S second);
/**
* Extract partial CRDT state from given state, which contains only the
* changes to it since given timestamp.
*
* If there were no changes, then this method must return null.
*
* Suppose we have some CRDT value 'old', which is the state of something
* either exactly at or after the timestamp.
*
* This method should create a CRDT value that, when combined with 'old',
* gives you 'state', which is 'old' updated to current time.
*
* Basically this is almost like taking a CRDT diff betweend 'old' and 'state'.
*
* It can be a huge optimization e.g. for big CRDT maps:
*
* The whole map state could contain thousands of key-value pairs,
* and instead of combining 'old' with 'state' (which with CRDT would achieve the most complete map)
* that requires serializing, transfering and/or storing the whole 'state',
* one could extract only the entries that are changed between 'old' and 'state',
* serialize and transfer only those and then CRDT-combine those with 'old', achieving the
* same result with much less resources spent.
*/
@Nullable
S extract(S state, long timestamp);
static > CrdtFunction ofCrdtType() {
return new CrdtFunction() {
@Override
public S merge(S first, S second) {
return first.merge(second);
}
@Nullable
@Override
public S extract(S state, long timestamp) {
return state.extract(timestamp);
}
};
}
}