prometheus

master / unreleased

[CHANGE] NewLeveledCompactor takes a context so that a compaction is canceled when closing the db.
[ENHANCEMENT] When closing the db any running compaction will be cancelled so it doesn't block.
[CHANGE] prometheus_tsdb_storage_blocks_bytes_total is now prometheus_tsdb_storage_blocks_bytes

[CHANGE] New WALSegmentSize option to override the DefaultOptions.WALSegmentSize. Added to allow using smaller wal files. For example using tmpfs on a RPI to minimise the SD card wear out from the constant WAL writes. As part of this change the DefaultOptions.WALSegmentSize constant was also exposed.
[CHANGE] Empty blocks are not written during compaction #374
[FEATURE] Size base retention through Options.MaxBytes. As part of this change:
- added new metrics - prometheus_tsdb_storage_blocks_bytes_total, prometheus_tsdb_size_retentions_total, prometheus_tsdb_time_retentions_total
- new public interface SizeReader: Size() int64
- OpenBlock signature changed to take a logger.
[REMOVED] PrefixMatcher is considered unused so was removed.
[CLEANUP] Options.WALFlushInterval is removed as it wasn't used anywhere.
[FEATURE] Add new LiveReader to WAL pacakge. Added to allow live tailing of a WAL segment, used by Prometheus Remote Write after refactor. The main difference between the new reader and the existing Reader is that for LiveReader a call to Next() that returns false does not mean that there will never be more data to read.

[BUGFIX] Fixed most windows test and some actual bugs for unclosed file readers.

[CHANGE] LastCheckpoint() used to return just the segment name and now it returns the full relative path.
[CHANGE] NewSegmentsRangeReader() can now read over miltiple wal ranges by using the new SegmentRange{} struct.
[CHANGE] CorruptionErr{} now also exposes the Segment Dir which is added when displaying any errors.
[CHANGE] Head.Init() is changed to Head.Init(minValidTime int64)
[CHANGE] SymbolTable() renamed to SymbolTableSize() to make the name consistent with the Block{ symbolTableSize uint64 } field.
[CHANGE] wal.Reader{} now exposes Segment() for the current segment being read and Offset() for the current offset. -[FEATURE] tsdbutil analyze subcomand to find churn, high cardinality, etc.