Many claims exists out there that recommend migrate to exadata and drop all your indexes, but lets see how smart scan processing works with various types of index access through a series of tests. For columns with fewer than 200 distinct values, the storage index creates a very compact inmemory representation of the dictionary and uses this. It processes queries in an intelligent way, retrieving specific rows rather than the complete blocks. Now, exadata use flash cache more intelligently for utilization of storing oracle database, this feature is called as exadata smart flash cache. This post was written in 2012 and covers the exadata x2 model. Of course this is one of the mail feature of exadata software. The exadata software can simultaneously scan from flash and disk to maximize bandwidth. Decision to do smart scan or not is made on the runtime execution.
Deep sleep peaceful floating meditation l cleanse your spirit l relax mind body l positive mindset duration. Oracle asm disk group force dismount and compromise data availability. Oracle enterprise manager 12c provides a unified view of oracle exadata hardware and software with deep insight into the health and performance of all components such as the database servers, infiniband switches, oracle exadata storage. It processes queries in an intelligent way, retrieving. As many of you will know, oracle has introduced a new flagship in the core area. Only the data requested in the query is returned to the database server. Smart scan critically depends on direct read in order to read the synthetic output blocks into private buffers in pga so with direct read disabled smart scan is also disabled.
That information is what gives the storage index its power as, during a smart scan as tasks are offloaded to the storage cells, exadata scans these storage indexes for columns and values of interest. Exadata provides not only smart scans but at least a couple of ways to monitor them. Later it had been increased to be used within the oltp databases moreover. If an io operation is meant to be in flash cache it will go otherwise it will go to. Please see some speed comparison below with and without smart scan. Exadata on whole is the server machine using both the database software and hardware server. Several new features were introduced for oracle exadata system software. Smart scans can definitely improve throughput by using the various optimizations to reduce the amount of data read and the volume of data returned to the database servers. Jul 16, 2017 in exadata and cell smart table scan and cell smart index scans are used, then you can check the proportion of reads that are actually using smartscan cell physical io bytes eligible for predicate offload. I have no plans to update it to cover the later models, so please be aware that the information below is no longer be up to date.
To that end, both of these configurations benefit from hardwareassist decryption via the ipp libarary. Perhaps surprisingly, we still did a normal full table scan, not a smart scan, contrary to whats documented on mos. Notice that i didnt highlight table scans in this case, because exadata uses sql. Storage indexes are a feature unique to the exadata database machine whose primary goal is to reduce the amount of io required to service io requests for exadata smart scan. How to get smart scan to engage when direct read was introduced a short list of exceptions was added and one was on recursive serial queries, we have filed er bug 30905358 from containers table scans are not offloaded to track the request to relax the restriction on recursive queries in a future release. Revolutionary park systems smartscan automatizes the atomic. New features for oracle exadata system software release 12. Storage servers, or cells, that run exadata storage server software, which manages io requests coming from database servers. Gathered all interview questions on exadata from various websites into one place here. Smart scans are part of what kerry osborne calls the secret sauce of exadata, and hes right. Exadata smart scan offloads processing of queries from the database server to the storage server. I publish this article to show that systematic exadata performance troubleshooting techniques arent fundamentally different from existing nonexadata techniques, especially the starting point of troubleshooting. When updating a system with oracle exadata system software release 12. Here, we are discussing smart scan a feature of exadata database machine that can be used for data warehouse and oltp environment and will compare this with traditional oracle database management system.
The new smartscan operating software for park afm systems revolutionizes atomic force microscopy by automatizing the imaging process, transforming how. Here are some sample statistics taken from an actual production system. Somehow i had got the impression that the esfc was storing parts of the smart scan results. Extensive endtoend testing ensures all software components supplied with oracle exadata database machine work seamlessly together my oracle support doc id 888828. The theory of course, based on previous testing, is that the time should approach the. Sep 23, 2014 then when you are on exadata and cell smart table scan and cell smart index scans are used, then you can check the proportion of reads that are actually using smartscan. The exadata database machine is a combined hardware.
This unconventional split architecture aims to minimize data transfer through io processing done by storage servers using smart scan software. Top 3 latest oracle exadata interview questions 2019. Technically this term is called as exadata smart scan. Theres even a bug explaining that closed as not a bug exadata smartscan is not being used on insert as selectarticle id 48116. Nov 08, 2011 this video provides information on using exadata smart scan. So, when your select statement may use smart scan and be really fast, the same select operation in an insert select or updatedelete context will not end up using smart scans by default. Both the x22 and x28 are attached to westmere epbased storage servers. Storage arrays are already bottlenecked, and adding flash just exposes the bottlenecks even more. Processors on the exadata storage server process the data on behalf of the database sql query. So in esence, smart scan doesnt offload virtual column filtering. This is the amount of reads in bytes that are going to the smartscan code. How to measure exadata smartscan efficiency blog dbi services.
In contrast, each exadata rack combines compute servers and storage servers over an infiniband network. Many claims exists out there that recommend migrate to exadata and drop all your indexes, but lets see how smart scan processing works with various types of index access. Smart scan is a subset of cell offload processing and. Jul 10, 2011 smart scan on exadata and direct path reads. If you are preparing for oracle exadata interview questions for experienced or freshers, you are at the right place to get the best questions and answers. Dec 20, 2019 oracle exadata interview questions 2019. Oracle exadata interview questions and answers gologica. The best oracle exadata interview questions updated 2020. Below are the oracle exadata database interview questions and answers which makes you comfortable to face the interviews. The secret sauce for exadata is its ability to offload processing to the storage tier. It is not different from the general databases but the architecture involving servers results in high speed, low latency. Starting with oracle exadata system software release 12.
Note that for simplicity i ran this test case in serial execution mode, which still is able to use serial direct path reads and s mart scan. Let start with listing smart scan requirements here. Such writes are later written back to the disks when the disks are less busy. Oracle grid infrastructure supports mixed version for limited duration for the purposes of rolling update only for example, updating from release 12. From a pure brute force hardware standpoint, oracle offers fast. Also refer to note find the statistics related to cell offload doc id 1438173. What happens if we force a full scan on the query via a hint. So if you dont see smart scan happening with full table index scan, its probably serial query not doing direct path read. With exadata smart scan processing, exadata is capable of offloading a large portion of a querys workload to the storage cells.
In these two cases the restriction is on using direct read on serial recursive queries. A dba can easily estimate the impact of this change. Offloading and smart scan are two terms that are used somewhat interchangeably. This article provides a view on how this new feature provides performance improvements on exadata hardware in comparison to a conventional database hardware. Exadata smart flash cache understand different type of database io and take cache decision according to io type. You can disable the smart scan feature in session level by using following commands. The exadata cluster permits for consistent performance whereas permitting raised turnout. Smart scan feature is introduced for improving query performance. A new feature of exadata software is the smart scan feature which enhances the database performance many times over. When an oracle exadata database machine is deployed, all of the software described in the table is installed and configured to deliver high performance and availability for oracle database. This video provides information on using exadata smart scan. Exadata was designed to address the most common bo8leneck for. This is how normal smart scan waits should look like, no single block ios and most of time is spent waiting for cell smart table scan or of course running on cpu.
Exadata smart scan offload enhancements for inmemory aggregation ima. Forcing smart scans on exadata umair mansoobs blog. Unlike the better known smart scanning features though, storage indexes have an important advantage. It shows how exadata smart scan is indicated in the query execution plan along with various statistics and wait events that can be used. May 23, 2016 as you can see that direct path read is required for smart scan.
If data is not being accessed via smart scan the blocks are returned to the database host and buffered in the sga see the seven fundamentals. Significant cpu savings can be made within the database server by offloading the cpuintensive decryption task to exadata cells. Can the exadata smart flash cache slow smart scans. For example, the oracle exadata database machine feature smart scan offload for compressed index scan requires oracle database 12. Smart scan works in conjunction with exadata hybrid columnar compression so that column projection and row filtering can be executed along with decompression at the storage level to save cpu cycles on the database. Troubleshooting exadata v2 smart scan performance tech. Optimizer can predict if smart scan can be used and will mention it in execution plan. After receiving the excellent expert oracle exadata book i decided to. Aug 19, 2010 deep sleep peaceful floating meditation l cleanse your spirit l relax mind body l positive mindset duration. The smart software automatically improves vendor name. Epson scansmart accounting edition includes all standard scansmart features plus powerful receipt management functionality. If shutting down the storage server could lead to an asm disk group force. New features for oracle exadata system software release 18. Smart scan as many of you will know, oracle has introduced a new flagship in the core area.
Automatically extract and categorize key data into multiple fields vendor, total price, tax, date, payment method, card type and card number. How to measure exadata smartscan efficiency blog dbi. The exadata smart flash cache feature of the exadata storage server software intelligently caches database objects in flash memory, replacing slow, mechanical io operations to disk with. Smart scan and recursive queries oracle smartscan deep dive.
Exadata was originally designed for the warehouse setting. Smart scan and recursive queries oracle smartscan deep. Then when you are on exadata and cell smart table scan and cell smart index scans are used, then you can check the proportion of reads that are actually using smartscan. A total flash storage of 384gb per cell is available on the exadata appliance. Offloading is a more generic term that means doing work at the storage tier that would otherwise have to be done on the database tier this can include work that is not. Study the latest exadata interview questions today here. The oracle dbms software has always run on virtually any hardware platform. It hosts operating systems, cpu memory, and hard drives. Exadata does have another feature, storage indexes, aimed at avoiding the need to read from disk at all as well as the smart flash cache which attempts to keep useful data blocks on flash storage, but the basic smart scan operation does not avoid the need to perform reads. The exadata flash cache makes use of flash memory to speed up access to commonly used data.
Parallel queries automatically use direct path read and serial queries may use direct path read. Somehow i had got the impression that the esfc was storing parts of the smart scan results kind of like the result set cache. If the storage index contains the desired column and the minimum and maximum values dont fall within the desired range that 1 mb segment is skipped. After all, exadata is just an oracle database which happens to be able to intelligently communicate with its storage to avoid unnecessarily moving too much data around. But if you will see from execution plan that storage access will be used to filter predicates it doesnt mean that on runtime smartscan will be implemented. In exadata and cell smart table scan and cell smart index scans are used, then you can check the proportion of reads that are actually using smartscan cell physical io bytes eligible for predicate offload.
Comparing ibm power systems and oracle exadata database. Smart scan allows oracle databases to push query information down to the storage level, specifically. One of the key enablers of this is the exadata smart flash cache hardware and the intelligent oracle exadata storage server software that drives it. That means 2,660,000 iops in flash, through the storage servers, across the network, and into the database servers. Flash caches on pure columnar data in flash run faster because they read only the selected columns, reducing flash ios and storage. All i wanted was a huge table to see if a smart scan really is so mind.
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