remove unused WALFlushInterval option and NopWAL struct (#468)

The WALFlushInterval is not used anywhere in the code base.
The WAL is not an interface anymore to save some lookup time so can't use NopWAL in the tests. Instead can just pass nil as the code checks for that and it is essentially a noop.

Signed-off-by: Krasi Georgiev <kgeorgie@redhat.com>

CHANGELOG.md

@@ -1,8 +1,9 @@
 ## master / unreleased
  - [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.
+ - [CLEANUP] `Options.WALFlushInterval` is removed as it wasn't used anywhere.
 
 ## 0.3.1
-- [BUGFIX] Fixed most windows test and some actual bugs for unclosed file readers.
+ - [BUGFIX] Fixed most windows test and some actual bugs for unclosed file readers.
 
 ## 0.3.0
  - [CHANGE] `LastCheckpoint()` used to return just the segment name and now it returns the full relative path.

cmd/tsdb/main.go

@@ -130,7 +130,6 @@ func (b *writeBenchmark) run() {
 	l = log.With(l, "ts", log.DefaultTimestampUTC, "caller", log.DefaultCaller)
 
 	st, err := tsdb.Open(dir, l, nil, &tsdb.Options{
-		WALFlushInterval:  200 * time.Millisecond,
 		RetentionDuration: 15 * 24 * 60 * 60 * 1000, // 15 days in milliseconds
 		BlockRanges:       tsdb.ExponentialBlockRanges(2*60*60*1000, 5, 3),
 	})

db.go

@@ -44,7 +44,6 @@ import (
 // DefaultOptions used for the DB. They are sane for setups using
 // millisecond precision timestamps.
 var DefaultOptions = &Options{
-	WALFlushInterval:  5 * time.Second,
 	WALSegmentSize:    wal.DefaultSegmentSize,
 	RetentionDuration: 15 * 24 * 60 * 60 * 1000, // 15 days in milliseconds
 	BlockRanges:       ExponentialBlockRanges(int64(2*time.Hour)/1e6, 3, 5),
@@ -53,9 +52,6 @@ var DefaultOptions = &Options{
 
 // Options of the DB storage.
 type Options struct {
-	// The interval at which the write ahead log is flushed to disk.
-	WALFlushInterval time.Duration
-
 	// Segments (wal files) max size
 	WALSegmentSize int
 

wal.go

@@ -94,27 +94,6 @@ type WAL interface {
 	Close() error
 }
 
-// NopWAL is a WAL that does nothing.
-func NopWAL() WAL {
-	return nopWAL{}
-}
-
-type nopWAL struct{}
-
-func (nopWAL) Read(
-	seriesf func([]RefSeries),
-	samplesf func([]RefSample),
-	deletesf func([]Stone),
-) error {
-	return nil
-}
-func (w nopWAL) Reader() WALReader                     { return w }
-func (nopWAL) LogSeries([]RefSeries) error             { return nil }
-func (nopWAL) LogSamples([]RefSample) error            { return nil }
-func (nopWAL) LogDeletes([]Stone) error                { return nil }
-func (nopWAL) Truncate(int64, func(uint64) bool) error { return nil }
-func (nopWAL) Close() error                            { return nil }
-
 // WALReader reads entries from a WAL.
 type WALReader interface {
 	Read(