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DBBuffer
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neustore.base</FONT>
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Class DBBuffer</H2>
<PRE>
java.lang.Object
<IMG SRC="../../resources/inherit.gif" ALT="extended by"><B>neustore.base.DBBuffer</B>
</PRE>
<DL>
<DT><B>Direct Known Subclasses:</B> <DD><A HREF="../../neustore/base/LRUBuffer.html" title="class in neustore.base">LRUBuffer</A></DD>
</DL>
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<DL>
<DT>public abstract class <B>DBBuffer</B><DT>extends java.lang.Object</DL>
<P>
Abstract base class for a buffer manager. It helps index structures (derived from <A HREF="../../neustore/base/DBIndex.html" title="class in neustore.base"><CODE>DBIndex</CODE></A>) manage disk pages. <p> <b>Usage:</b><br> <ul> <li> An application can choose to use a provided sub-class like LRUBuffer. <li> If the user chooses to define their own buffer management, they should derive a class from <code>DBBuffer</code> by providing methods <code>add</code>, <code>find</code> and <code>flush</code>. <li> The user typically calls <A HREF="../../neustore/base/DBBuffer.html#readPage(java.io.RandomAccessFile, int)"><CODE>readPage(java.io.RandomAccessFile, int)</CODE></A> and <A HREF="../../neustore/base/DBBuffer.html#writePage(java.io.RandomAccessFile, int, neustore.base.DBPage)"><CODE>writePage(java.io.RandomAccessFile, int, neustore.base.DBPage)</CODE></A> to read/write a disk page. Here <code>readPage</code> returns an object of class <code>DBBufferReturnedElement</code>. Besides the page itself, the returned element also specifies the nodeType and whether the node was parsed. If parsed, the returned object is of class DBPage. Otherwise, the returned object is a byte array and it's up to the application to generate a DBPage object. Moreover, nodeType=-1 and 0 are reserved (for DBByteArrayPage and DBEmptyPage). The application can explain the other values. For example, a B+-tree may cast a nodeType=1 node to an index node. <li> The user can <A HREF="../../neustore/base/DBBuffer.html#pin(java.io.RandomAccessFile, int)"><CODE>pin(java.io.RandomAccessFile, int)</CODE></A> or <A HREF="../../neustore/base/DBBuffer.html#unpin(java.io.RandomAccessFile, int)"><CODE>unpin(java.io.RandomAccessFile, int)</CODE></A> a page. <li> The user can call <A HREF="../../neustore/base/DBBuffer.html#getIOs()"><CODE>getIOs()</CODE></A> to get statistics, or call <A HREF="../../neustore/base/DBBuffer.html#clearIOs()"><CODE>clearIOs()</CODE></A> to initialize the counters. </ul>
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<DL>
<DT><B>Author:</B></DT> <DD>Tian Xia <tianxia@ccs.neu.edu><br>Donghui Zhang <donghui@ccs.neu.edu></DD><DT><B>See Also:</B><DD><A HREF="../../neustore/base/DBIndex.html" title="class in neustore.base"><CODE>DBIndex</CODE></A>, <A HREF="../../neustore/base/DBPage.html" title="class in neustore.base"><CODE>DBPage</CODE></A></DL>
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<B>Constructor Summary</B></FONT></TD>
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<TD><CODE><B><A HREF="../../neustore/base/DBBuffer.html#DBBuffer(int, int)">DBBuffer</A></B>(int bufferSize, int pageSize)</CODE>
<BR>
Opens an existing Database file.</TD>
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<CODE> void</CODE></FONT></TD>
<TD><CODE><B><A HREF="../../neustore/base/DBBuffer.html#clearIOs()">clearIOs</A></B>()</CODE>
<BR>
Resets the four counters <code>bufferReadIO</code>, etc.</TD>
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<CODE> int[]</CODE></FONT></TD>
<TD><CODE><B><A HREF="../../neustore/base/DBBuffer.html#getIOs()">getIOs</A></B>()</CODE>
<BR>
Reports the disk/buffer I/Os. </TD>
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<CODE> void</CODE></FONT></TD>
<TD><CODE><B><A HREF="../../neustore/base/DBBuffer.html#pin(java.io.RandomAccessFile, int)">pin</A></B>(java.io.RandomAccessFile file, int pageID)</CODE>
<BR>
Pins a page. </TD>
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<TD ALIGN="right" VALIGN="top" WIDTH="1%"><FONT SIZE="-1">
<CODE> <A HREF="../../neustore/base/DBBufferReturnElement.html" title="class in neustore.base">DBBufferReturnElement</A></CODE></FONT></TD>
<TD><CODE><B><A HREF="../../neustore/base/DBBuffer.html#readPage(java.io.RandomAccessFile, int)">readPage</A></B>(java.io.RandomAccessFile file, int pageID)</CODE>
<BR>
Returns a buffered page. </TD>
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<CODE> void</CODE></FONT></TD>
<TD><CODE><B><A HREF="../../neustore/base/DBBuffer.html#unpin(java.io.RandomAccessFile, int)">unpin</A></B>(java.io.RandomAccessFile file, int pageID)</CODE>
<BR>
Unpins a page. </TD>
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<TD ALIGN="right" VALIGN="top" WIDTH="1%"><FONT SIZE="-1">
<CODE> void</CODE></FONT></TD>
<TD><CODE><B><A HREF="../../neustore/base/DBBuffer.html#writePage(java.io.RandomAccessFile, int, neustore.base.DBPage)">writePage</A></B>(java.io.RandomAccessFile file,⌨️ 快捷键说明
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