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Oracle Dba Case Studies

Oracle index rebuilding - indexes to rebuild script Oracle index rebuilding - indexes to rebuild script
Executive Summary on index rebuilding. While it may be rare to rebuild an Oracle index for performance reasons, there are some databases that will get a ...

Oracle Dba Case Studies

Using these metrics, we can analyze the system and produce some very interesting reports of index internals                         average      average                average             average  average           leaf     leaf row     average leaf block              height   blocks           rows       length leaf blocks     length             ------- -------- -------------- ------------ ----------- ----------                   1      236             12          234           1      7,996                   2      317         33,804      691,504         106      7,915                   3    8,207      1,706,685   41,498,749       7,901      7,583             as we see, we can compute and spin this data in an almost infinite variety of ways. Sushil kumar of oracle corporation, kumar states that the new automatic maintenance tasks (amt) oracle10g feature will automatically detect and re-build sub-optimal indexes. The automated maintenance tasks infrastructure enables the oracle database to automatically perform those operations.

Rather, oracle logically deletes the index entry and leaves dead nodes in the index tree. Oracle 10g, and ill bet that any smart six year-old can install sql server. However, the 10g segment advisor only recommends index rebuilding from a space reclamation perspective, not for performance.

For now, the most any oracle professional can do is to explore their indexes and learn how the software manages b-tree structures. This is a multi-block read access where the index blocks are accessed via a db file scattered read to load index blocks into the buffers. This large section of space is more likely to be reused than many tiny chunks.

Now that we have a table that will hold all of the index details, the next step is to populate the table with data from freshly-analyzed indexes. I cant speak for the average dba, but ive personally managed over 50 oracle databases, and with the proper automation in-place, a good dba can manage hundreds of instances. The view contains a great deal of important information for the sql optimizer, but there is still more to see.

At my previous job, our observation was that on 20 million row tables and upward as little as 5 deletes, regardless of other factors, would cause sufficient performance degradation to justify an index rebuild. Oracle?s cost-based sql optimizer relies heavily upon  - as an index accepts new rows, the index blocks split. When can we prove a benefit from an index rebuild?  Here, robin schumacher that is rebuilt in a larger tablespace will contain more index entries be block, and have a flatter structure as you can see, the amount of logical reads has been reduced in half simply by using the new 16k tablespace and accompanying 16k data cache.

Oracle index that has four or more levels would benefit from rebuilding. Index                  keys        keys      leaf rows  height      per access --------------------  ------       -----     --------   ------      ----- custidx                   1     423,209       58,282        4          6 eduidx12               433      36,272        7,231        3          2 custidx                  12   1,262,393      726,361        4          6 the term deleted leaf node refers to the number of index nodes that have been logically deleted as a result of row operations. Now i ask you, how do you expect a dba to react when reading an article that is focused on reducing the dba staff size?  I know how managers think, and this article could wind-up in the wrong hands ( over the years, ive read enough jaded studies to suspect when a study may be biased, so i did some checking. Getting a meaningful measure of the benefit of an index rebuild in a production environment is very difficult because the system is under heavy load and usage patterns change constantly. Only indexes that have a high number of deleted leaf blocks and are accessed in these ways will benefit from rebuilding getting statistically valid proof from a volatile production system would be a phenomenal challenge.


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Oracle Dba Case Studies

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Oracle Dba Case Studies Hence, an oracle index may have four levels, Oracle author, notes that it is often difficult to pinpoint the exact reason that indexes benefit from a rebuild the dbas were pulling out their hair until they noticed that the size of the indexes were too large for the amount of data in the tables, and remembered this old myth?. The number of gets per access refers to the amount of logical io that is required to fetch a row with the index. Now that we have a table that will hold all of the index details, the next step is to populate the table with data from freshly-analyzed indexes. In a large production system, it would be a massive effort to trace lio from specific queries to specific indexes before and after the rebuild, There are many myths and legends surrounding the use of oracle indexes, especially the ongoing passionate debate about rebuilding of indexes for improving performance. Awr provides the oracle database 10g a very good knowledge of how it is being used. Linux is far more powerful than windows i cant believe people are actually paid to come up with these numbers.
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    This is because if ), then the rows are added in order, and the index is likely to reuse the deleted leaf nodes. Plus, in a trick worthy of machiavelli, you can claim that the numbers prove the assertion with a confidence interval of two standard deviations!  For an example of broad numbers, in the study whitepaper we see this estimation of the salaries of sql server vs. At the bottom of that page, also note this site hosted for microsoft by alinean, inc. Here is the script that i use to get all index details. Oracle 10g the results revealed that, overall, microsoft sql server 2005 required significantly less effort to install and maintain than oracle database 10g.

    The quote below caught my eye because it reminded me of an infomercial i saw last night that used exactly the same phrase on average, the annual cost for administration is 2,847 per year per database for microsoft sql server 2005 and 10,206 per year per database for oracle 10g. We can also use the data from our detail table to compute our own metrics. The pragmatists are not interested in proving? Anything, they are just happy that the end-users are happy. This script detects indexes for rebuilding using these rules  it is very difficult to write a script that will identify indexes that will benefit from rebuilding because it depends on how the indexes are used. Hence, an oracle index may have four levels, but only in those areas of the index tree where the massive inserts have occurred.

    At my previous job, our observation was that on 20 million row tables and upward as little as 5 deletes, regardless of other factors, would cause sufficient performance degradation to justify an index rebuild. Remember that oracle leaves dead index nodes in the index when rows are deleted. And for the largest databases, oracle appears to be slightly less expensive to administer. Now that we have a table that will hold all of the index details, the next step is to populate the table with data from freshly-analyzed indexes. While it is tempting to write a script that rebuilds every index in the schema, bear in mind that oracle contains many thousands of indexes, and a complete rebuild can be very time consuming. In scientific applications (clinical, laboratory) where large datasets are added and removed, the need to rebuild indexes is common. If in the table segment) then the index key is in the same order as the table rows and index range scans will be very efficient, with minimal disk io. Even if index rebuilding were to be proven as a useless activity, the placebo effect on the end-users is enough to justify the task. The default view (view segments recommended to shrink) lists any segments that have free space you can reclaim. Here are thepros and cons of this highly emotional issue   many oracle shops schedule periodic index rebuilding, and report measurable speed improvements after they rebuild their oracle b-tree indexes.

    "On average, the annual cost for administration is $2,847 per year per database for Microsoft SQL Server 2005 and $10,206 per year per database for Oracle 10g.

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    Oracle 10g, and ill bet that any smart six year-old can install sql server. Oracle otn published this korn shell script to identify highly fragmented indexes, targeting indexes that are 4 levels or more, or indexes with a high number of deleted leaf blocks select exec dbmsstats. And for the largest databases, oracle appears to be slightly less expensive to administer. So who is right?  I suspect that they both are correct. The conclusion also sets tiny cut-offs for a database of reasonable size, perhaps not understanding that sql server is used for data volumes that could be kept inside a spreadsheet.

    For example, indexes that are always accessed vis an index unique scan will never need rebuilding, because the dead space does not interfere with the index access Buy now Oracle Dba Case Studies

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    Remember, you should always run , we must loop through iterations of the analyze index xxx validate structure command to populate our table with other statistics. To see the commonality between indexes of similar nature you can use the data from your new table to write summary queries (listing 5). Here is a sample of index-based access plans   this row access method scans an index to collect a series of rowid?s. However with 70 different metrics for each index, it can be quite confusing about which columns are the most important. Here is the script that i use to get all index details.

    An oracle ace notes this script to rebuild his indexes. In an oltp system, index space is often greater than the space allocated for tables, and fast row data access is critical for sub-second response time Oracle Dba Case Studies Buy now

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    Also, note the categorization of large volumes of users in the methodology section of the research study. The following code snippets are used to generate the report. On the other hand, if ), and the majority of queries use the index with fast-full scans or index range scans, then a rebuild of the underlying table (to is close to the number of blocks, indicating that the rows are in the same sequence as the index. Here are thepros and cons of this highly emotional issue   many oracle shops schedule periodic index rebuilding, and report measurable speed improvements after they rebuild their oracle b-tree indexes. Would leave a dense cluster of deleted leaf nodes on adjacent data blocks within the index tablespace Buy Oracle Dba Case Studies at a discount

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    And for the largest databases, oracle appears to be slightly less expensive to administer. Oracle author, notes that it is often difficult to pinpoint the exact reason that indexes benefit from a rebuild the dbas were pulling out their hair until they noticed that the size of the indexes were too large for the amount of data in the tables, and remembered this old myth?, and decided to try rebuilding the indexes on these tables. Oranges comparison, computerworld tries to sensationalize a administration costs. Now i ask you, how do you expect a dba to react when reading an article that is focused on reducing the dba staff size?  I know how managers think, and this article could wind-up in the wrong hands ( over the years, ive read enough jaded studies to suspect when a study may be biased, so i did some checking Buy Online Oracle Dba Case Studies

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    So, what do we make of this study?  It starts by correctly noting that human costs comprise the majority of it budget, and that reducing the number expensive dbas is an area of opportunity for the it manager to save money. In systems that do batch dml jobs, index rebuilding often improves sql performance. Windows xp sp2, and found  let?s start by creating a table to hold our index data. Oracle 10g the results revealed that, overall, microsoft sql server 2005 required significantly less effort to install and maintain than oracle database 10g. This is dependent on the dbblocksize.

    And for the largest databases, oracle appears to be slightly less expensive to administer. The query reads a table we built called tablemodifications that we loaded each night from dbatabmodifications before we ran statistics Buy Oracle Dba Case Studies Online at a discount

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    Some experts suspect a placebo effect may be at work here, and the end-users, knowing that they have new index trees, report a performance gain when none exists. The default view (view segments recommended to shrink) lists any segments that have free space you can reclaim. Thats a savings of more than 350 in annual costs per database for the microsoft platform. One vexing issue with oracle indexes is that the information for an index rebuild must be gathered from two sources once we gather information from these sources, we can generate a report with everything we need to know about the index internal structure                     rep       dist. And for the largest databases, oracle appears to be slightly less expensive to administer Oracle Dba Case Studies For Sale

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    Hence, an oracle index may have four levels, but only in those areas of the index tree where the massive inserts have occurred. For now, the most any oracle professional can do is to explore their indexes and learn how the software manages b-tree structures. I cant speak for the average dba, but ive personally managed over 50 oracle databases, and with the proper automation in-place, a good dba can manage hundreds of instances. Today, a battle is raging between the academics? Who do not believe that indexes should be rebuilt without expensive studies, and the pragmatists? Who rebuild indexes on a schedule because their end-users report faster response times. One vexing issue with oracle indexes is that the information for an index rebuild must be gathered from two sources once we gather information from these sources, we can generate a report with everything we need to know about the index internal structure                     rep       dist For Sale Oracle Dba Case Studies

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    We can take this same approach and attempt to answer the followingquestions 1 - at what point does an index spawn to another level (height)?  It should be a function of blocksize, key length and the number of keys. Monitoring must be turned on to use the dbatabmodifications table. And for the largest databases, oracle appears to be slightly less expensive to administer. The default view (view segments recommended to shrink) lists any segments that have free space you can reclaim. Rather, oracle logically deletes the index entry and leaves dead nodes in the index tree.

    This execution plan combines bitmap indexes to quickly resolve a low-cardinality boolean expression while the internals of oracle indexing are very complex and open to debate, there are some things that you can do to explore the internal structures of your indexes Sale Oracle Dba Case Studies

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