metrics: move Compression to Table

It will be useful to expose separate compression metrics for sstable
and blob value data; move `Metrics.Compression` to `Table` and add a
TODO to add one for blob files.

Author: RaduBerinde

db.go

@@ -2186,7 +2186,7 @@ func (d *DB) Metrics() *Metrics {
 	for i := 0; i < numLevels; i++ {
 		metrics.Levels[i].Additional.ValueBlocksSize = *valueBlockSizeAnnotator.LevelAnnotation(vers.Levels[i])
 		compressionMetrics := compressionStatsAnnotator.LevelAnnotation(vers.Levels[i])
-		metrics.Compression.MergeWith(compressionMetrics)
+		metrics.Table.Compression.MergeWith(compressionMetrics)
 	}
 
 	metrics.Table.PendingStatsCollectionCount = int64(len(d.mu.tableStats.pending))

metrics.go

@@ -348,6 +348,8 @@ type Metrics struct {
 		BackingTableCount uint64
 		// The sum of the sizes of the BackingTableCount sstables that are backing virtual tables.
 		BackingTableSize uint64
+		// Compression statistics for sstable data (does not include blob files).
+		Compression CompressionMetrics
 
 		// Local file sizes.
 		Local struct {
@@ -437,9 +439,9 @@ type Metrics struct {
 			// ZombieCount is the number of local zombie blob files.
 			ZombieCount uint64
 		}
-	}
 
-	Compression CompressionMetrics
+		// TODO(radu): add compression stats.
+	}
 
 	FileCache FileCacheMetrics
 
@@ -489,15 +491,16 @@ type Metrics struct {
 	manualMemory manual.Metrics
 }
 
-// CompressionMetrics contains compression metrics for sstables and blob files.
+// CompressionMetrics contains compression metrics for sstables or blob files.
 type CompressionMetrics struct {
 	// NoCompressionBytes is the total number of bytes in files that do are not
 	// compressed. Data can be uncompressed when 1) compression is disabled; 2)
 	// for certain special types of blocks; and 3) for blocks that are not
 	// compressible.
 	NoCompressionBytes uint64
-	// CompressedBytesWithoutStats is the total number of bytes in files that do not
-	// encode compression statistics (or for which there are no statistics yet).
+	// CompressedBytesWithoutStats is the total number of bytes in files that do
+	// not encode compression statistics (or for which there are no statistics
+	// yet).
 	CompressedBytesWithoutStats uint64
 	Snappy                      CompressionStatsForSetting
 	MinLZ                       CompressionStatsForSetting
@@ -1016,13 +1019,13 @@ func (m *Metrics) String() string {
 	cur = cur.WriteString(compressionTableHeader).NewlineReturn()
 	compressionContents := []pair[string, CompressionStatsForSetting]{
 		{k: "none", v: CompressionStatsForSetting{
-			CompressedBytes:   m.Compression.NoCompressionBytes,
-			UncompressedBytes: m.Compression.NoCompressionBytes,
+			CompressedBytes:   m.Table.Compression.NoCompressionBytes,
+			UncompressedBytes: m.Table.Compression.NoCompressionBytes,
 		}},
-		{k: "snappy", v: m.Compression.Snappy},
-		{k: "minlz", v: m.Compression.MinLZ},
-		{k: "zstd", v: m.Compression.Zstd},
-		{k: "unknown", v: CompressionStatsForSetting{CompressedBytes: m.Compression.CompressedBytesWithoutStats}},
+		{k: "snappy", v: m.Table.Compression.Snappy},
+		{k: "minlz", v: m.Table.Compression.MinLZ},
+		{k: "zstd", v: m.Table.Compression.Zstd},
+		{k: "unknown", v: CompressionStatsForSetting{CompressedBytes: m.Table.Compression.CompressedBytesWithoutStats}},
 	}
 	compressionContents = slices.DeleteFunc(compressionContents, func(p pair[string, CompressionStatsForSetting]) bool {
 		return p.v.CompressedBytes == 0

metrics_test.go

@@ -129,6 +129,14 @@ func exampleMetrics() Metrics {
 	m.Table.ZombieCount = 18
 	m.Table.BackingTableCount = 1
 	m.Table.BackingTableSize = 2 * MB
+	m.Table.Compression.NoCompressionBytes = 100 * MB
+	m.Table.Compression.CompressedBytesWithoutStats = 500 * MB
+	m.Table.Compression.Snappy.CompressedBytes = 1 * GB
+	m.Table.Compression.Snappy.UncompressedBytes = 2 * GB
+	m.Table.Compression.MinLZ.CompressedBytes = 1 * GB
+	m.Table.Compression.MinLZ.UncompressedBytes = 3 * GB
+	m.Table.Compression.Zstd.CompressedBytes = 10 * GB
+	m.Table.Compression.Zstd.UncompressedBytes = 50 * GB
 	m.Table.Local.LiveSize = 28 * GB
 	m.Table.Local.LiveCount = 10_000
 	m.Table.Local.ObsoleteSize = 29 * MB
@@ -155,15 +163,6 @@ func exampleMetrics() Metrics {
 	m.BlobFiles.Local.ZombieSize = 30 * MB
 	m.BlobFiles.Local.ZombieCount = 14
 
-	m.Compression.NoCompressionBytes = 100 * MB
-	m.Compression.CompressedBytesWithoutStats = 500 * MB
-	m.Compression.Snappy.CompressedBytes = 1 * GB
-	m.Compression.Snappy.UncompressedBytes = 2 * GB
-	m.Compression.MinLZ.CompressedBytes = 1 * GB
-	m.Compression.MinLZ.UncompressedBytes = 3 * GB
-	m.Compression.Zstd.CompressedBytes = 10 * GB
-	m.Compression.Zstd.UncompressedBytes = 50 * GB
-
 	m.FileCache.Size = 1 * MB
 	m.FileCache.TableCount = 180
 	m.FileCache.BlobFileCount = 181