feat(buffer): LRU buffer replacement strategy

Author: amrdb

simpledb/buffer/Buffer.java

@@ -4,97 +4,107 @@
 import simpledb.log.LogMgr;
 
 /**
- * An individual buffer. A databuffer wraps a page 
+ * An individual buffer. A databuffer wraps a page
  * and stores information about its status,
  * such as the associated disk block,
  * the number of times the buffer has been pinned,
  * whether its contents have been modified,
  * and if so, the id and lsn of the modifying transaction.
+ *
  * @author Edward Sciore
  */
 public class Buffer {
-   private FileMgr fm;
-   private LogMgr lm;
-   private Page contents;
-   private BlockId blk = null;
-   private int pins = 0;
-   private int txnum = -1;
-   private int lsn = -1;
+    private FileMgr fm;
+    private LogMgr lm;
+    private int id; // Added for HW3
+    private Page contents;
+    private BlockId blk = null;
+    private int pins = 0;
+    private int txnum = -1;
+    private int lsn = -1;
 
-   public Buffer(FileMgr fm, LogMgr lm) {
-      this.fm = fm;
-      this.lm = lm;
-      contents = new Page(fm.blockSize());
-   }
-   
-   public Page contents() {
-      return contents;
-   }
+    public Buffer(FileMgr fm, LogMgr lm, int id) {
+        this.fm = fm;
+        this.lm = lm;
+        this.id = id;
+        contents = new Page(fm.blockSize());
+    }
 
-   /**
-    * Returns a reference to the disk block
-    * allocated to the buffer.
-    * @return a reference to a disk block
-    */
-   public BlockId block() {
-      return blk;
-   }
+    public int getId() {
+        return id;
+    }
 
-   public void setModified(int txnum, int lsn) {
-      this.txnum = txnum;
-      if (lsn >= 0)
-         this.lsn = lsn;
-   }
+    public Page contents() {
+        return contents;
+    }
 
-   /**
-    * Return true if the buffer is currently pinned
-    * (that is, if it has a nonzero pin count).
-    * @return true if the buffer is pinned
-    */
-   public boolean isPinned() {
-      return pins > 0;
-   }
-   
-   public int modifyingTx() {
-      return txnum;
-   }
+    /**
+     * Returns a reference to the disk block
+     * allocated to the buffer.
+     *
+     * @return a reference to a disk block
+     */
+    public BlockId block() {
+        return blk;
+    }
 
-   /**
-    * Reads the contents of the specified block into
-    * the contents of the buffer.
-    * If the buffer was dirty, then its previous contents
-    * are first written to disk.
-    * @param b a reference to the data block
-    */
-   void assignToBlock(BlockId b) {
-      flush();
-      blk = b;
-      fm.read(blk, contents);
-      pins = 0;
-   }
-   
-   /**
-    * Write the buffer to its disk block if it is dirty.
-    */
-   void flush() {
-      if (txnum >= 0) {
-         lm.flush(lsn);
-         fm.write(blk, contents);
-         txnum = -1;
-      }
-   }
+    public void setModified(int txnum, int lsn) {
+        this.txnum = txnum;
+        if (lsn >= 0)
+            this.lsn = lsn;
+    }
 
-   /**
-    * Increase the buffer's pin count.
-    */
-   void pin() {
-      pins++;
-   }
+    /**
+     * Return true if the buffer is currently pinned
+     * (that is, if it has a nonzero pin count).
+     *
+     * @return true if the buffer is pinned
+     */
+    public boolean isPinned() {
+        return pins > 0;
+    }
 
-   /**
-    * Decrease the buffer's pin count.
-    */
-   void unpin() {
-      pins--;
-   }
+    public int modifyingTx() {
+        return txnum;
+    }
+
+    /**
+     * Reads the contents of the specified block into
+     * the contents of the buffer.
+     * If the buffer was dirty, then its previous contents
+     * are first written to disk.
+     *
+     * @param b a reference to the data block
+     */
+    void assignToBlock(BlockId b) {
+        flush();
+        blk = b;
+        fm.read(blk, contents);
+        pins = 0;
+    }
+
+    /**
+     * Write the buffer to its disk block if it is dirty.
+     */
+    void flush() {
+        if (txnum >= 0) {
+            lm.flush(lsn);
+            fm.write(blk, contents);
+            txnum = -1;
+        }
+    }
+
+    /**
+     * Increase the buffer's pin count.
+     */
+    void pin() {
+        pins++;
+    }
+
+    /**
+     * Decrease the buffer's pin count.
+     */
+    void unpin() {
+        pins--;
+    }
 }