log: improve error messages in compact()

lib/log/index.js

@@ -712,7 +712,10 @@ function Log(filename, opts) {
     }
     await p(onDrain)()
     const [err1] = await p(onOverwritesFlushed)()
-    if (err1) return cb(err1)
+    if (err1) {
+      // prettier-ignore
+      return cb(new Error('Compact failed to pre-flush overwrites', { cause: err1 }))
+    }
 
     const startCompactTimestamp = Date.now()
     compacting = true
@@ -724,7 +727,7 @@ function Log(filename, opts) {
     const [err2] = await p(fs.unlink.bind(fs))(filenameNew)
     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}))
+      return cb(new Error('Compact failed to get rid of previous compacting log', { cause: err2 }))
     }
 
     const rafNew = RAF(filenameNew)
@@ -808,7 +811,8 @@ function Log(filename, opts) {
     if (err3) {
       await p(rafNew.close.bind(rafNew))()
       compacting = false
-      return cb(err3)
+      // prettier-ignore
+      return cb(new Error('Compact failed while scanning-sifting the old log', { cause: err3 }))
     }
     await writeBlock(latestBlockIndexNew, latestBlockBufNew)
 
@@ -819,12 +823,14 @@ function Log(filename, opts) {
     ])
     if (err4 ?? err5) {
       compacting = false
-      return cb(err4 ?? err5)
+      // prettier-ignore
+      return cb(new Error('Compact failed to close log files', { cause: err4 ?? err5 }))
     }
     const [err6] = await p(fs.rename.bind(fs))(filenameNew, filename)
     if (err6) {
       compacting = false
-      return cb(err6)
+      // prettier-ignore
+      return cb(new Error('Compact failed to replace old log with new', { cause: err6 }))
     }
     raf = RAF(filename)
     latestBlockBuf = latestBlockBufNew
@@ -838,9 +844,10 @@ function Log(filename, opts) {
     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)
-    })
+    const [err7] = await p(saveStats)()
+    if (err7) {
+      return cb(new Error('Compact failed to save stats file', { cause: err7 }))
+    }
     compactionProgress.set({ percent: 1, done: true, sizeDiff, holesFound })
     for (const callback of waitingCompaction) callback()
     waitingCompaction.length = 0