log: show compaction duration in debugging

lib/log/index.js

@@ -717,6 +717,7 @@ function Log(filename, opts) {
     const [err1] = await p(onOverwritesFlushed)()
     if (err1) return cb(err1)
 
+    const startCompactTimestamp = Date.now()
     compacting = true
     if (compactionProgress.value.done) {
       compactionProgress.set(COMPACTION_PROGRESS_START)
@@ -724,7 +725,10 @@ function Log(filename, opts) {
 
     const filenameNew = filename + '.compacting'
     const [err2] = await p(fs.unlink.bind(fs))(filenameNew)
-    if (err2 && err2.code !== 'ENOENT') return cb(err2)
+    if (err2 && err2.code !== 'ENOENT') {
+      // prettier-ignore
+      return cb(new Error('Failed to get rid of previous compaction file when starting a new compact', {cause: err2}))
+    }
 
     const rafNew = RAF(filenameNew)
 
@@ -834,6 +838,8 @@ function Log(filename, opts) {
     const sizeDiff = oldTotalBytes - getTotalBytes()
     lastRecOffset.set(nextSince)
     compacting = false
+    const duration = Date.now() - startCompactTimestamp
+    debug2('Completed in %d ms', duration)
     deletedBytes = 0
     saveStats(function onSavedStatsAfterCompaction(err) {
       if (err) debug2('Failed to save stats file: %s', err.message)
@@ -904,17 +910,17 @@ function Log(filename, opts) {
 
   return {
     // Public API:
-    scan: onLoad(scan), // TODO
-    del: onLoad(del), // TODO
-    append: onLoad(append), // TODO
-    overwrite: onLoad(overwrite), // TODO
-    close: onLoad(close), // TODO
-    onDrain: onLoad(onDrain), // TODO
+    scan: onLoad(scan),
+    del: onLoad(del),
+    append: onLoad(append),
+    overwrite: onLoad(overwrite),
+    close: onLoad(close),
+    onDrain: onLoad(onDrain),
     onOverwritesFlushed: onLoad(onOverwritesFlushed),
-    compact: onLoad(compact), // TODO
+    compact: onLoad(compact),
     compactionProgress,
     lastRecOffset,
-    stats, // TODO
+    stats,
 
     // Useful for tests
     _get: onLoad(get),