Method getEmptyPage

src/java/simpledb/index/BTreeFile.java:1175–1192

Method to encapsulate the process of creating a new page. It reuses old pages if possible, and creates a new page if none are available. It wipes the page on disk and in the cache and returns a clean copy locked with read-write permission @param tid - the transaction id @param dirtypages - the li

(TransactionId tid, Map<PageId, Page> dirtypages, int pgcateg)

	 * @throws TransactionAbortedException
	 */
	private Page getEmptyPage(TransactionId tid, Map<PageId, Page> dirtypages, int pgcateg)
			throws DbException, IOException, TransactionAbortedException {
		// create the new page
		int emptyPageNo = getEmptyPageNo(tid, dirtypages);
		BTreePageId newPageId = new BTreePageId(tableid, emptyPageNo, pgcateg);
		
		// write empty page to disk
		RandomAccessFile rf = new RandomAccessFile(f, "rw");
		rf.seek(BTreeRootPtrPage.getPageSize() + (long) (emptyPageNo - 1) * BufferPool.getPageSize());
		rf.write(BTreePage.createEmptyPageData());
		rf.close();
		
		// make sure the page is not in the buffer pool	or in the local cache		
		Database.getBufferPool().discardPage(newPageId);
		dirtypages.remove(newPageId);
		
		return getPage(tid, dirtypages, newPageId, Permissions.READ_WRITE);
	}

	/**
	 * Mark a page in this BTreeFile as empty. Find the corresponding header page