Change Data Capture consumers often update a search index, cache, or read model from database changes. Once events pass through partitions and parallel workers, an older change may arrive after a newer one. A consumer must prevent that late event from rolling its projection backward.
Design a CdcProjection class:
CdcProjection() creates an empty projection.boolean apply(String key, int version, String operation, String value) applies a change when version is strictly newer than every previously accepted version for key. It returns whether the change was accepted.String get(String key) returns the current value, or "" when the key is missing or deleted.
operation is either "upsert" or "delete". An upsert stores value. A delete removes the visible value but retains its version as a tombstone. Equal versions are duplicates and must be rejected. Versions belong to individual keys, not to the projection as a whole.
Example 1:
Input:
Output:
Explanation: Version 3 deletes the row and leaves a tombstone. The late version-2 upsert is rejected, so it cannot resurrect the deleted row.
Example 2:
Input:
Output:
Explanation: Key a and key b have independent version histories.
Constraints
1 <= key.length <= 1000 <= version <= 10^9operation is "upsert" or "delete".- Upsert values are non-empty and have length at most
1000; the value passed with a delete is ignored. - At most
10^5 total calls are made.
Apply Ordered CDC Changesmedium