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Although it is well known that indexes will enhance database performance, you will need to understand how to make them work well for you Placing unnecessary or inappropriate indexes on your table may prove to be detrimental to performance Here are some guidelines for creating efficient indexes for your Oracle tables: Index only if you need to access no more than 10 or 15 percent of the data in a table The alternative to using an index to access row data in a table is to read the entire table sequentially from top to bottom, which is called a full table scan Full table scans are better for queries that require a high percentage of the data in a table Remember that using indexes to retrieve rows requires two reads: an index read followed by a table read Avoid indexes on relatively small tables.

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Full table scans are just fine for small tables There s no need to store both table and index data for small tables Create primary keys for all tables When you designate a column as a primary key, Oracle automatically creates an index on the column Index the columns that are involved in multi-table join operations Index columns that are used frequently in WHERE clauses Index the columns that are involved in ORDER BY and GROUP BY operations, or other operations, such as UNION and DISTINCT, that involve sorting Because indexes are already sorted, the sorting necessary to perform the previously mentioned operations will be considerably reduced Columns that consist of long character strings are usually poor candidates for indexing Columns that are frequently updated should ideally not be indexed because of the overhead involved Index tables with high selectivity only.

That is, choose to index tables where few rows have similar values Keep the number of indexes small Composite indexes may need to be used where single-column values may not be unique by themselves In composite indexes, the driving or the first column should be the most selective column Always keep in mind the golden rule of indexing a table: The index on a table should be based on the types of queries you expect to occur against the table s columns You can create more than one index on a table; you can choose to create an index on column X, or column Y, or both, and you can also create a composite index on both columns X and Y You will make the right decisions about which index to create by thinking about the most frequent types of queries involving the table s data..

#!/bin/sh fs="/" fs_total=`df -k $fs | tail -n 1 | awk '{print $2}'` fs_used=`df -k $fs | tail -n 1 | awk '{print $3}'` percent_used=$((100*$fs_used/$fs_total)) echo "$fs is at ${percent_used}% capacity"

The EXCLUDE and INCLUDE parameters are mutually exclusive. You can use one or the other, not both simultaneously in the same job.

When you filter metadata by using the EXCLUDE or INCLUDE parameters, remember that all objects that depend on any of the filtered objects are processed in the same fashion as the filtered object. For example, when you use the EXCLUDE parameter to exclude a table, you ll also be automatically excluding the indexes, constraints, triggers, and so on that are dependent on the table.

call the finalizer to perform last-chance cleanup before memory of an undestructed object is reclaimed. This is helpful to ensure reliable cleanup of non-memory resources, but it can also be the source of pitfalls like the finalization timing race condition or the graph promotion problem. Furthermore, normal finalizers are often not reliable enough for long-running servers like SQL Server 2005. To further increase reliability, the CLR version 2.0 introduces CERs, which ensure that regions of constrained code cannot be interrupted by an asynchronous exception. One way to avoid these pitfalls and to benefit from CERs is the use of the SafeHandle base class.

The QUERY parameter serves the same function as it does in the traditional export utility: it lets you selectively export table row data with the help of a SQL statement. However, the parameter is enhanced for Oracle Database 10g by permitting you to qualify the SQL statement with a table name, so that it applies only to a particular table. Here s an example: QUERY=OE.ORDERS: "WHERE order_id > 100000" In this example, only those rows in the orders table (owned by user OE) where the order_id is greater than 100000 are exported.