Open db in Read only mode (#588)

* Added db read only open mode and use it for the tsdb cli.

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

CHANGELOG.md

@@ -1,4 +1,9 @@
-## Master / unreleased
+## master / unreleased
+
+ - [FEATURE] Added `DBReadOnly` to allow opening a database in read only mode.
+    - `DBReadOnly.Blocks()` exposes a slice of `BlockReader`s.
+    - `BlockReader` interface - removed MinTime/MaxTime methods and now exposes the full block meta via `Meta()`.
+
 
  - [FEATURE] `chunckenc.Chunk.Iterator` method now takes a `chunckenc.Iterator` interface as an argument for reuse.
 

block.go

@@ -138,11 +138,8 @@ type BlockReader interface {
 	// Tombstones returns a TombstoneReader over the block's deleted data.
 	Tombstones() (TombstoneReader, error)
 
-	// MinTime returns the min time of the block.
-	MinTime() int64
-
-	// MaxTime returns the max time of the block.
-	MaxTime() int64
+	// Meta provides meta information about the block reader.
+	Meta() BlockMeta
 }
 
 // Appendable defines an entity to which data can be appended.

block_test.go

@@ -175,8 +175,7 @@ func TestBlockSize(t *testing.T) {
 			testutil.Ok(t, blockInit.Close())
 		}()
 		expSizeInit = blockInit.Size()
-		actSizeInit, err := testutil.DirSize(blockInit.Dir())
-		testutil.Ok(t, err)
+		actSizeInit := testutil.DirSize(t, blockInit.Dir())
 		testutil.Equals(t, expSizeInit, actSizeInit)
 	}
 
@@ -185,7 +184,7 @@ func TestBlockSize(t *testing.T) {
 		testutil.Ok(t, blockInit.Delete(1, 10, labels.NewMustRegexpMatcher("", ".*")))
 		expAfterDelete := blockInit.Size()
 		testutil.Assert(t, expAfterDelete > expSizeInit, "after a delete the block size should be bigger as the tombstone file should grow %v > %v", expAfterDelete, expSizeInit)
-		actAfterDelete, err := testutil.DirSize(blockDirInit)
+		actAfterDelete := testutil.DirSize(t, blockDirInit)
 		testutil.Ok(t, err)
 		testutil.Equals(t, expAfterDelete, actAfterDelete, "after a delete reported block size doesn't match actual disk size")
 
@@ -199,8 +198,7 @@ func TestBlockSize(t *testing.T) {
 			testutil.Ok(t, blockAfterCompact.Close())
 		}()
 		expAfterCompact := blockAfterCompact.Size()
-		actAfterCompact, err := testutil.DirSize(blockAfterCompact.Dir())
-		testutil.Ok(t, err)
+		actAfterCompact := testutil.DirSize(t, blockAfterCompact.Dir())
 		testutil.Assert(t, actAfterDelete > actAfterCompact, "after a delete and compaction the block size should be smaller %v,%v", actAfterDelete, actAfterCompact)
 		testutil.Equals(t, expAfterCompact, actAfterCompact, "after a delete and compaction reported block size doesn't match actual disk size")
 	}