From 869076ff603b374d700465340b19ebd87ca601b6 Mon Sep 17 00:00:00 2001
From: Alex Gaetano Padula <apadula@cursusdb.com>
Date: Wed, 30 Oct 2024 02:21:50 -0400
Subject: [PATCH] flushing correction on clearing memtable and minor commenting
 a variety of functions

---
 k4.go | 32 ++++++++++++++++++++------------
 1 file changed, 20 insertions(+), 12 deletions(-)

diff --git a/k4.go b/k4.go
index f03deb0..99becb9 100644
--- a/k4.go
+++ b/k4.go
@@ -283,6 +283,7 @@ func (k4 *K4) Close() error {
 }
 
 // printLog prints a log message to the log file or stdout
+// takes a string message
 func (k4 *K4) printLog(msg string) {
 	if k4.logging {
 		log.Println(msg)
@@ -290,14 +291,18 @@ func (k4 *K4) printLog(msg string) {
 }
 
 // backgroundWalWriter writes operations to the write ahead log
+// This function runs in the background and pops operations from the wal queue and writes
+// to write ahead log.  The reason we do this is to optimize write speed
 func (k4 *K4) backgroundWalWriter() {
-	defer k4.wg.Done()
+	defer k4.wg.Done() // Defer completion of routine
+
 	for {
-		k4.walQueueLock.Lock()
-		if len(k4.walQueue) > 0 {
-			op := k4.walQueue[0]
-			k4.walQueue = k4.walQueue[1:]
-			k4.walQueueLock.Unlock()
+		k4.walQueueLock.Lock() // lock up the wal queue
+
+		if len(k4.walQueue) > 0 { // Check if there are operations in the wal queue
+			op := k4.walQueue[0]          // Get the first operation
+			k4.walQueue = k4.walQueue[1:] // Remove the first operation
+			k4.walQueueLock.Unlock()      // Unlock the wal queue
 
 			// Serialize operation
 			data := serializeOp(op.Op, op.Key, op.Value)
@@ -305,10 +310,12 @@ func (k4 *K4) backgroundWalWriter() {
 			// Write to WAL
 			_, err := k4.wal.Write(data)
 			if err != nil {
-				k4.printLog(fmt.Sprintf("Failed to write to WAL: %v", err))
+				k4.printLog(fmt.Sprintf("Failed to write to WAL: %v", err)) // Log error
 			}
 		} else {
-			k4.walQueueLock.Unlock()
+			k4.walQueueLock.Unlock() // Unlock the wal queue
+			// We will sleep for a bit to avoid CPU bursts
+			time.Sleep(28 * time.Millisecond)
 		}
 
 		select {
@@ -339,7 +346,7 @@ func serializeOp(op OPR_CODE, key, value []byte) []byte {
 		return nil
 	}
 
-	return buf.Bytes()
+	return buf.Bytes() // return the encoded bytes
 
 }
 
@@ -351,7 +358,6 @@ func deserializeOp(data []byte) (OPR_CODE, []byte, []byte, error) {
 	dec := gob.NewDecoder(bytes.NewReader(data)) // Create a new decoder
 
 	err := dec.Decode(&operation) // Decode the operation
-
 	if err != nil {
 		return 0, nil, nil, err
 	}
@@ -397,9 +403,11 @@ func deserializeKv(data []byte) (key, value []byte, err error) {
 
 // loadSSTables loads SSTables from the directory
 func (k4 *K4) loadSSTables() {
-	// Open configured directory
+	// Open configured K4 directory
+
 	dir, err := os.Open(k4.directory)
 	if err != nil {
+		k4.printLog(fmt.Sprintf("Failed to open directory: %v", err))
 		return
 	}
 
@@ -505,7 +513,7 @@ func (k4 *K4) flushMemtable() error {
 	k4.sstables = append(k4.sstables, sstable)
 
 	// Clear memtable
-	skiplist.NewSkipList(k4.memtableMaxLevel, k4.memtableP)
+	k4.memtable = skiplist.NewSkipList(k4.memtableMaxLevel, k4.memtableP)
 
 	k4.printLog("Flushed memtable")