Modifications are not visible within transaction

[yoshinorim]

rocksdb.delete test case failed because deletes were not visible within transaction. Transactions are are currently started with GetSnapshot().

[yoshinorim]

So far I have found that changes are not visible when doing non-locking, range or full table scan.

I think the root cause is that changes (Rdb_transaction.changes -- Row_table)
are ignored at ha_rocksdb::rnd_next_with_direction() for non-locking
reads. For example, 1. create empty table, 2. begin; 3. insert; 4. select; => then select returns empty result. I confirmed scan_it->Valid() returned false at ha_rocksdb::rnd_next_with_direction(), without checking trx->changes.

I think merging trx->changes and scan_it is needed. I assume secondary index scan also needs merging too. Merging means:

1. key existing only on trx->changes (including tombstone) => use trx->changes
2. key existing only on scan_it => use scan_it
3. key existing both (including tombstone) => use trx->changes

2 and 3 would be easy. 1 needs more discussions about how to implement efficiently.

[yoshinorim]

I pushed rocksdb.transaction test case to cover insert/update/delete.

[yoshinorim]

https://reviews.facebook.net/D31551 fixed this issue.