Here's my understanding. The others can correct me if I'm mistaken. Samza provides the changelog functionality by intercepting RocksDB "put" and "delete" operations. However, TTL is managed by RocksDB internally and there aren't any hooks exposed in the RocksDB JNI. So there are 2 problems that arise with TTL and change logging: 1. Samza doesn't know when an entry expires, so it can't delete the expired entry from the changelog. 2. The changelog currently has no concept of entry age/timestamp, so when the changelog is restored, it's unknown whether some subset (or all) of the entries should be immediately expired.
These issues aren't insurmountable, but they weren't pursued for the initial implementation. Perhaps because there was a shortage of use cases that needed both TTL and changelogging, but I'm not sure. -Jake On Wed, Jan 27, 2016 at 6:19 PM, David Garcia <dgar...@homeaway.com.invalid> wrote: > So, I saw this very scary message: > > > ERROR - e.kv.RocksDbKeyValueStore$ - sessionJoinStore is a TTL based > store, changelog is not supported for TTL based stores, use at your own > discretion > > > > > A few of questions: > > 1.) Does this mean that this store is NOT backed by the changelog? > > 2.) Provided that the store IS backed by a change log, do the TTL > expirations commit removals from the changelog (I.e. Nulls)...presumably > upon compaction > > 3.) Can I please get a bit more detail on how TTL affects a changelog > store? > > > -David >
