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package simpledb;

/**

* Page is the interface used to represent pages that are resident in the

* BufferPool. Typically, DbFiles will read and write pages from disk.

* <p>

* Pages may be "dirty", indicating that they have been modified since they

* were last written out to disk.

*

* For recovery purposes, pages MUST have a single constructor of the form:

* Page(PageId id, byte[] data)

*/

public interface Page {

/**

* Return the id of this page. The id is a unique identifier for a page

* that can be used to look up the page on disk or determine if the page

* is resident in the buffer pool.

*

* @return the id of this page

*/

public PageId getId();

/**

* Get the id of the transaction that last dirtied this page, or null if the page is clean..

*

* @return The id of the transaction that last dirtied this page, or null

*/

public TransactionId isDirty();

/**

* Set the dirty state of this page as dirtied by a particular transaction

*/

public void markDirty(boolean dirty, TransactionId tid);

/**

* Generates a byte array representing the contents of this page.

* Used to serialize this page to disk.

* <p>

* The invariant here is that it should be possible to pass the byte array

* generated by getPageData to the Page constructor and have it produce

* an identical Page object.

*

* @return A byte array correspond to the bytes of this page.

*/

public byte[] getPageData();

/** Provide a representation of this page before any modifications were made

to it. Used by recovery.

*/

public Page getBeforeImage();

/*

* a transaction that wrote this page just committed it.

* copy current content to the before image.

*/

public void setBeforeImage();

}