/**
* Compares one PageId to another.
*
* @param o The object to compare against (must be a PageId)
* @return true if the objects are equal (e.g., page numbers and table ids are the same)
*/
public boolean equals(Object o) {
if (!(o instanceof PageId)) return false;
PageId other = (PageId) o;
if (this.getTableId() != other.getTableId() || this.pageNumber() != other.pageNumber())
return false;
return true;
}
/**
* Retrieve the specified page with the associated permissions. Will acquire a lock and may block
* if that lock is held by another transaction.
*
* <p>The retrieved page should be looked up in the buffer pool. If it is present, it should be
* returned. If it is not present, it should be added to the buffer pool and returned. If there is
* insufficient space in the buffer pool, an page should be evicted and the new page should be
* added in its place.
*
* @param tid the ID of the transaction requesting the page
* @param pid the ID of the requested page
* @param perm the requested permissions on the page
* @throws IOException
* @throws NoSuchElementException
*/
public Page getPage(TransactionId tid, PageId pid, Permissions perm)
throws TransactionAbortedException, DbException, NoSuchElementException, IOException {
if (this.deadPool.containsKey(pid)) {
return this.deadPool.get(pid);
} else {
if (this.deadPool.size() >= this.numPages) {
throw new DbException("Too many pages!");
} else {
this.deadPool.put(
pid, Database.getCatalog().getDatabaseFile(pid.getTableId()).readPage(pid));
return this.deadPool.get(pid);
}
}
}
/**
* Flushes a certain page to disk
*
* @param pageId an ID indicating the page to flush
*/
private synchronized void flushPage(PageId pageId) throws IOException {
if (pageIdToPages.containsKey(pageId)) {
Page page = pageIdToPages.get(pageId);
// append an update record to the log, with
// a before-image and after-image.
TransactionId dirtier = page.isDirty();
if (dirtier != null) {
addDirtiedFlushedPage(dirtier, pageId);
Database.getLogFile().logWrite(dirtier, page.getBeforeImage(), page);
Database.getLogFile().force();
Database.getCatalog().getDatabaseFile(pageId.getTableId()).writePage(page);
page.markDirty(false, null);
}
}
}
/**
* Retrieve the specified page with the associated permissions. Will acquire a lock and may block
* if that lock is held by another transaction.
*
* <p>The retrieved page should be looked up in the buffer pool. If it is present, it should be
* returned. If it is not present, it should be added to the buffer pool and returned. If there is
* insufficient space in the buffer pool, an page should be evicted and the new page should be
* added in its place.
*
* @param tid the ID of the transaction requesting the page
* @param pid the ID of the requested page
* @param perm the requested permissions on the page
* @throws DbException
* @throws TransactionAbortedException
*/
public Page getPage(TransactionId tid, PageId pid, Permissions perm)
throws DbException, TransactionAbortedException {
lockManager.acquireLock(tid, pid, perm);
if (pageIdToPages.containsKey(pid)) {
return pageIdToPages.get(pid);
}
if (currentPages.get() == maxPages) {
evictPage();
}
int tableId = pid.getTableId();
Catalog catalog = Database.getCatalog();
DbFile dbFile = catalog.getDatabaseFile(tableId);
Page page = dbFile.readPage(pid);
pageIdToPages.put(pid, page);
currentPages.incrementAndGet();
return page;
}
