Method logWrite

src/java/simpledb/storage/LogFile.java:200–222

Write an UPDATE record to disk for the specified tid and page (with provided before and after images.) @param tid The transaction performing the write @param before The before image of the page @param after The after image of the page @see Page#getBef

(TransactionId tid, Page before,
                                       Page after)

        @see Page#getBeforeImage
    */
    public  synchronized void logWrite(TransactionId tid, Page before,
                                       Page after)
        throws IOException  {
        Debug.log("WRITE, offset = " + raf.getFilePointer());
        preAppend();
        /* update record conists of

           record type
           transaction id
           before page data (see writePageData)
           after page data
           start offset
        */
        raf.writeInt(UPDATE_RECORD);
        raf.writeLong(tid.getId());

        writePageData(raf,before);
        writePageData(raf,after);
        raf.writeLong(currentOffset);
        currentOffset = raf.getFilePointer();

        Debug.log("WRITE OFFSET = " + currentOffset);
    }

    void writePageData(RandomAccessFile raf, Page p) throws IOException{
        PageId pid = p.getId();