fork of https://github.com/oxigraph/rocksdb and https://github.com/facebook/rocksdb for nextgraph and oxigraph

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Dhruba Borthakur 47c4191fe8 Reduce write amplification by merging files in L0 back into L0 ... Summary: There is a new option called hybrid_mode which, when switched on, causes HBase style compactions. Files from L0 are compacted back into L0. This meat of this compaction algorithm is in PickCompactionHybrid(). All files reside in L0. That means all files have overlapping keys. Each file has a time-bound, i.e. each file contains a range of keys that were inserted around the same time. The start-seqno and the end-seqno refers to the timeframe when these keys were inserted. Files that have contiguous seqno are compacted together into a larger file. All files are ordered from most recent to the oldest. The current compaction algorithm starts to look for candidate files starting from the most recent file. It continues to add more files to the same compaction run as long as the sum of the files chosen till now is smaller than the next candidate file size. This logic needs to be debated and validated. The above logic should reduce write amplification to a large extent... will publish numbers shortly. Test Plan: dbstress runs for 6 hours with no data corruption (tested so far). Differential Revision: https://reviews.facebook.net/D11289		12 years ago
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leveldb	Reduce write amplification by merging files in L0 back into L0	12 years ago
utilities	Bring read_only into ttl	12 years ago