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<p><b>Новая страница</b></p><div>== Handling Large Objects in the Database==<br />
<br />
<p>To address performance concerns, Oracle provides two options:</p><br />
<p>You can store the large objects internally, within the database itself (CLOB, BLOB).</p><br />
<p>You can keep the objects in the file system and just store the filenames in the database (BFILE).</p><br />
<p>CLOB (character large object): to store large amounts of character (text) information.</p><br />
<p>BLOB (binary large object): to store binary (mostly video/audio) information in the database.</p><br />
34. 1. Introduction<br />
34. 1. 1. <br />
Handling Large Objects in the Database<br />
34. 1. 2. <br />
<A href="/Tutorial/Oracle/0660__Large-Objects/LargeObjects.htm">Large Objects</a><br />
34. 1. 3. <br />
<A href="/Tutorial/Oracle/0660__Large-Objects/UsingCLOBsandBLOBs.htm">Using CLOBs and BLOBs</a><br />
<br />
== Large Objects==<br />
<br />
<p>Large objects (LOBs) may be used to store binary data, character data, and references to external files.</p><br />
<p>LOBs are widely used to store documents such as Word and PDF documents.</p><br />
<p>LOBs can store a maximum of 128 terabytes of data depending on the block size of your database.</p><br />
<p>There are four LOB types:</p><br />
<p>CLOB is the character LOB type.</p><br />
<p>CLOB is used to store character data.</p><br />
<p>NCLOB is the national language character LOB type.</p><br />
<p>NCLOB is used to store multiple byte character data (typically used for non-English characters).</p><br />
<p>BLOB is the binary LOB type.</p><br />
<p>BLOB is used to store binary data.</p><br />
<p>BFILE is the binary FILE type.</p><br />
<p>BFILE is used to store pointers to files located in the file system.</p><br />
<p>Columns created using CLOB and BLOB types have three advantages over those created using the older LONG and LONG RAW types:</p><br />
<p>LOB columns can store up to 128 terabytes of data.</p><br />
<p>This is far more data than you can store in a LONG and LONG RAW column.</p><br />
<p>A LONG and LONG RAW column may only store up to 2 gigabytes of data.</p><br />
<p>Note: The RAW type may store up to 4 kilobytes of data.</p><br />
<p>A table can have multiple LOB columns, but a table can only have one LONG or LONG RAW column.</p><br />
<p>LOB data can be accessed in random order.</p><br />
<p>LONG and LONG RAW data can only be accessed in sequential order.</p><br />
<p>A LOB consists of two parts:</p><br />
<p>The LOB locator A pointer that specifies the location of the LOB content.</p><br />
<p>The LOB content The actual character or byte data stored in the LOB.</p><br />
<p>Depending on the size of the LOB content, the actual data will either be stored in the table or out of the table.</p><br />
<p>If the LOB content is less than 4 kilobytes in size, the content is stored in the table containing the LOB column.</p><br />
<p>If it"s bigger, the content is stored outside the table.</p><br />
<p>With BFILE columns, only the locator is stored in the database-the locator points to the external file containing the LOB content.</p><br />
<p>Quote from:</p><br />
<p>Oracle Database 10g SQL (Osborne ORACLE Press Series) (Paperback)</p><br />
<p># Paperback: 608 pages</p><br />
<p># Publisher: McGraw-Hill Osborne Media; 1st edition (February 20, 2004)</p><br />
<p># Language: English</p><br />
<p># ISBN-10: 0072229810</p><br />
<p># ISBN-13: 978-0072229813</p><br />
34. 1. Introduction<br />
34. 1. 1. <br />
<A href="/Tutorial/Oracle/0660__Large-Objects/HandlingLargeObjectsintheDatabase.htm">Handling Large Objects in the Database</a><br />
34. 1. 2. <br />
Large Objects<br />
34. 1. 3. <br />
<A href="/Tutorial/Oracle/0660__Large-Objects/UsingCLOBsandBLOBs.htm">Using CLOBs and BLOBs</a><br />
<br />
== Using CLOBs and BLOBs==<br />
<br />
<p>LOB columns store a locator that points to the LOB contents.</p><br />
<p>Initializing a CLOB and BLOB</p><br />
<p>Before you can actually write content to a LOB, you must first initialize the LOB column.</p><br />
<p>You do this by calling an Oracle database function that generates and returns a value for the locator.</p><br />
<p>To initialize a CLOB or NCLOB column, you use the EMPTY_CLOB() function.</p><br />
<p>A BLOB column must be initialized using the EMPTY_BLOB() function.</p><br />
34. 1. Introduction<br />
34. 1. 1. <br />
<A href="/Tutorial/Oracle/0660__Large-Objects/HandlingLargeObjectsintheDatabase.htm">Handling Large Objects in the Database</a><br />
34. 1. 2. <br />
<A href="/Tutorial/Oracle/0660__Large-Objects/LargeObjects.htm">Large Objects</a><br />
34. 1. 3. <br />
Using CLOBs and BLOBs</div>Admin