clob

This article compares its performance with that of character large object (CLOB) and shredded XML storage.

This comparison is interesting because for a certain class of today's XML applications, CLOB columns are a commonly choice for XML storage.

I decided to use CLOBs (Character Large Objects) with a modern RDBMS to save these documents.

Storing the PO as a CLOB allows you to use the DOM in the application code to retrieve the relevant information.

Since the RDBMS supported a Java API to insert and retrieve CLOBs, this was a very easy task.

The parameter type used for XML documents in all the stored procedures is CLOB.

Only a blind full document retrieval, which again ignores the internal XML structure, can quickly read XML documents from CLOB columns.

This overhead does not exist when reading full XML documents from a CLOB where the XML is already stored in text form.

Selecting an XML column from a table also serializes its result into a CLOB.

Inserting the same XML data into a CLOB column takes approximately half the time (53%).

The CLOB data type is defined as a character large object capable of storing characters up to 2, 147, 483, 647 long.

An easy way to identify this problem is to temporarily use CLOB types, which have no size restrictions, as target columns.

Notice that inserting data to an XML column is no different from inserting into any CLOB column.

Note that XQUERY, by default, serializes its result set into a CLOB.

This is because CLOB inserts do not benefit as much from parallelism as XML column inserts.

Since logically the XML column appears the same as a VARCHAR, CLOB, or BLOB column, the INSERT statements are also similar.

Since CLOB inserts use direct writes, the file system cache is not needed and is pure overhead.

As expected, the elapsed insert time for both CLOB and XML columns is approximately linear in the number of documents inserted.

Another case is when you want to store a document in a database as a string or a Character Large Object (CLOB) without parsing it.

Many database systems allow you to store XML data as CLOBs or "shred" the data into relational tables.

Gone are the days of storing XML data as a CLOB or shredding to relational tables.

There is a code page conversion to the SQL world if the value is serialized into a CHAR, VARCHAR, or CLOB type that is not FOR BIT DATA.

The purchase order (PO) is stored as a CLOB in the relational database (as opposed to being shredded).

The other common technique is to simply dump your XML document inside a CLOB column in the database.

Even if the Chinese or Russian documents were inserted as BLOBs, they cannot be serialized as CLOBs or CHAR-types without giving this error.

Smart large objects consist of character large object (CLOB) and binary large object (BLOB) data types.

The above comparison shows the extreme impact of having a CLOB column, even a very short one.

You can choose to make the underlying storage a CLOB column, a VARCHAR column, or files within the file system.

Figure 3 shows that the increased workload intensity hurts CLOB performance drastically.

However, file system caching can help read operations on CLOB columns if no XML parsing is involved.

Prior to the DB2 9 release, XML data was either stored intact as a character large object (CLOB) or shredded to relational tables.

A response message is returned as character LOB (CLOB) if issued by the server.

Redirect the file into PDSQL using the operator, and pipe through a grep command, looking for CLOB fields.

Side tables can avoid much of the XML parsing for CLOBs and can often make CLOB queries 100 times faster or more.

This means that XML is either stored in files, stored wholesale in database CLOBs, or shredded into distinct columns.

The system generates a list of all of the CLOB fields found in the defect table (see Table 2).

It scales with the database, and XML-specific optimizations give it better performance than CLOBs.

At present, stored procedures and user-defined functions do not have support for XML as a parameter, but they can easily be passed as CLOBs.

Figure 5 shows the query performance (elapsed time) of all five test queries for both pureXML and CLOBs.

The larger messages should be read or received as CLOB.

The response message is returned as character LOB (CLOB).

Because the purchase order is stored as a CLOB in the relational database, we must use DOM to access the order date and individual products.

The result in Figure 1 shows the relative elapsed time between XML and CLOB column inserts (lower is better).

Indexed side tables are used to query the document that is retrieved as a CLOB.

The data processing extension OLE DB for Oracle does not support the following Oracle data types: BLOB, CLOB, NCLOB, BFILE, UROWID.

The current strategy of storing marked-up text in BLOBs, CLOBs, and VARCHARs isn't nearly as natural or efficient.

If XML documents are inserted into CLOB columns, they are inserted as unparsed text objects.

Also, in V6. 1, as described in the Information Center, the SQL type of the message changes from LONG VARCHAR to CLOB (see Figure 9).

Multi-user query tests were executed with 10 users on both CLOB and XML columns.

That's a nice improvement over working with XML data as CLOBs or VARCHARs, which require maximum lengths.

Using the either the Clob or Blob method is not an efficient way to upload large data.

If a table has a BLOB or CLOB column , you count row length using the LOB locator, not BLOB or CLOB data directly .

Don't log large data objects (CLOBs, DBCLOBs, and BLOBs) unless necessary.

Also, each entry can optionally have a BLOBDIR and CLOBDIR specification where in the BLOB and CLOB data are read or written.

This UDF expects a Character Large Object (CLOB) containing a mathematical formula (for example 3 5*17) as an input parameter.

CLOB values can be used with SQL Server 2005 large value data types.

All table spaces were defined with the no file system caching option, except where otherwise noted (for some of the CLOB storage tests)

If you use NCLOB or CLOB data types and run into a codepage or encoding conflict, you must do one of the following

Multi-user insert performance of XML compared to CLOB columns

Unstructured storage using CLOBs (also know as schema-less storage)