If elasticsearch controls the ID values as well as the documents
version we can optimize the code that adds / appends the documents
to the index. Essentially we an skip the version lookup for all
documents unless the same document is delivered more than once.
On the lucene level we can simply call IndexWriter#addDocument instead
of #updateDocument but on the Engine level we need to ensure that we deoptimize
the case once we see the same document more than once.
This is done as follows:
1. Mark every request with a timestamp. This is done once on the first node that
receives a request and is fixed for this request. This can be even the
machine local time (see why later). The important part is that retry
requests will have the same value as the original one.
2. In the engine we make sure we keep the highest seen time stamp of "retry" requests.
This is updated while the retry request has its doc id lock. Call this `maxUnsafeAutoIdTimestamp`
3. When the engine runs an "optimized" request comes, it compares it's timestamp with the
current `maxUnsafeAutoIdTimestamp` (but doesn't update it). If the the request
timestamp is higher it is safe to execute it as optimized (no retry request with the same
timestamp has been run before). If not we fall back to "non-optimzed" mode and run the request as a retry one
and update the `maxUnsafeAutoIdTimestamp` unless it's been updated already to a higher value
Relates to #19813
a0becd26b1