Andrew Kryczka ba0967b567 Reduce severity of too many levels log message (#5742)
Summary:
This condition is now a normal occurrence during write burst so there is
no need to warn the user about it. Here is a scenario where it happens
under completely normal conditions.

* Initially we have a DB of three levels (L0, L1, and L2) that is stable, i.e., compaction scores are all less than one.
* Now a write burst comes along. At first L0 blows up a bit in size as compaction hasn't had a chance to catch up.
* As a result of the above, `base_bytes_min` also increases since it is based on L0 size as of https://github.com/facebook/rocksdb/issues/4338
* If `base_bytes_min` increased enough (i.e., to be larger than L1), then we are shown the warning that the DB has more levels than necessary.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/5742

Differential Revision: D17059221

fbshipit-source-id: e4a31d6eea42089a8d273095f19653991bd91bea
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RocksDB: A Persistent Key-Value Store for Flash and RAM Storage

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RocksDB is developed and maintained by Facebook Database Engineering Team. It is built on earlier work on LevelDB by Sanjay Ghemawat (sanjay@google.com) and Jeff Dean (jeff@google.com)

This code is a library that forms the core building block for a fast key value server, especially suited for storing data on flash drives. It has a Log-Structured-Merge-Database (LSM) design with flexible tradeoffs between Write-Amplification-Factor (WAF), Read-Amplification-Factor (RAF) and Space-Amplification-Factor (SAF). It has multi-threaded compactions, making it specially suitable for storing multiple terabytes of data in a single database.

Start with example usage here: https://github.com/facebook/rocksdb/tree/master/examples

See the github wiki for more explanation.

The public interface is in include/. Callers should not include or rely on the details of any other header files in this package. Those internal APIs may be changed without warning.

Design discussions are conducted in https://www.facebook.com/groups/rocksdb.dev/

License

RocksDB is dual-licensed under both the GPLv2 (found in the COPYING file in the root directory) and Apache 2.0 License (found in the LICENSE.Apache file in the root directory). You may select, at your option, one of the above-listed licenses.

Description
A library that provides an embeddable, persistent key-value store for fast storage.
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