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Topic: Query plan

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	SQL Server Query Execution Plan Analysis
		As part of your analysis of an execution plan, you should focus some of your time on any part that takes more than one execution, and see if there is any way to reduce the number of executions performed.
		When you examine a graphical SQL Server query execution plan, one of the more useful things to look for are how indexes were used (if at all) by the query optimizer to retrieve data from tables from a given query.
		If the amount of data to be retrieved is large, relative to the size of the table, or if the data is not selective (which means that there are many rows with the same values in the same column), a table scan is often performed instead of an index seek because it is faster.
	www.sql-server-performance.com /tips/query_execution_plan_analysis_p2.aspx (1173 words)

	Query plan - Wikipedia, the free encyclopedia
		A query plan (or query execution plan) is an ordered set of steps used to access information in a SQL relational database management system.
		When a query is submitted to the database, the query optimizer evaluates all of the different possible plans for executing the query and returns what it considers the best alternative.
		Query plans are a very important tool in performance tuning of a query or database.
	en.wikipedia.org /wiki/Query_plan (229 words)

	CA Open Source Project Site - Ingres Query Execution Facility
		It is the query execution engine of Ingres, taking a compiled query plan and interpreting it to produce the desired query results This document discusses the architecture of QEF in detail sufficient to enable a dbms practitioner to understand its major control structures and flow of control.
		The execution algorithms of Ingres query plans are, of course, dictated by the structure of the query plans.
		Query plans consist of query trees corresponding to the separately optimized subqueries identified by OPF and action headers that tie the query trees together.
	opensource.ca.com /projects/ingres/documents/technical/qef (3202 words)

	MER Systems Inc. (Site not responding. Last check: 2007-10-31)
		Sorting and grouping: When a query is sorted by a field or fields which are the keys of an index, the index is used to retrieve the records in order rather than performing a sort.
		The plan clause itself can then be placed at the end of the query, guaranteeing that the plan will always be used by the query in retrieving the result set.
		Thus the PLAN writer must be familiar with the query which defines the view, and tell the optimizer how to retrieve the base tables in the view.
	www.mers.com /DJ1.HTML (2066 words)

	Performance Tips (Site not responding. Last check: 2007-10-31)
		Choosing the right plan to match the query structure and the properties of the data is absolutely critical for good performance.
		This plan will only have to visit 50 tuples because of the index, so it wins despite the fact that each individual fetch is more expensive than reading a whole disk page sequentially.
		In these queries, the time for the top plan node essentially is the time spent computing the new tuples and/or locating the old ones, but it doesn't include the time spent making the changes.
	www.ica.org.ve /guidox/bd/postgres/performance-tips.html (1506 words)

	[No title]
		Thu Aug 14 10:08:31 PDT 1997 Construction of the logical query plans ======================================= This document is valid as of 8/14/97.
		A canonicalized query plan consists of nodes which are subclasses of the Node class.
		As of February, 1997, a construction of a query plan for SelectListNode is the only case where a pointer to a PrefixSet object is passed as an argument, because we may get many results from an underneath plan.
	www-db.stanford.edu /~mchughj/loreimpl/queryproc.txt (1831 words)

	[No title] (Site not responding. Last check: 2007-10-31)
		Supervisor: S. Sudarshan Database queries are typically specified declaratively, and the database system has to choose an appropriate execution plan for the query.
		A query optimizer in a database system is responsible for transforming an SQL query into an execution plan.
		The cost of a query plan depends on many parameters such as predicate selectivities, available memory, and presence of access paths, whose values may not be known at optimization time.
	www.cse.iitb.ac.in /~aru/Thesis/Abstract.txt (452 words)

	BUG: SQL Server Books Online Incorrectly States That the Age Field of a Query Plan Is Incremented by Compilation Cost ... (Site not responding. Last check: 2007-10-31)
		The "Aging Execution Plans" section in the "Execution Plan Caching and Reuse" topic of SQL Server Books Online incorrectly states that each time a query plan that resides in the procedure cache is referenced by a connection, the age field of the query plan object is incremented by the compilation cost factor.
		Each query plan and execution context has an associated cost factor that indicates how expensive the structure is to compile.
		For example, if a query plan has a cost factor of 8, the age factor of the query plan is reset to 8 every time the query plan referenced for reuse.
	www.sunsite.org.uk /sites/ftp.microsoft.com/MISC/KB/en-us/825/728.HTM (269 words)

	查詢: [plan] - 線上英漢字典 (English-Chinese Dictionary)
		A draught or form; properly, a representation drawn on a plane, as a map or a chart; especially, a top view, as of a machine, or the representation or delineation of a horizontal section of anything, as of a building; a graphic representation; a diagram.
		A scheme devised; a method of action or procedure expressed or described in language; a project; as, the plan of a constitution; the plan of an expedition.
		To scheme; to devise; to contrive; to form in design; as, to plan the conquest of a country.
	cdict.giga.net.tw /query/plan (192 words)

	The execution plan in Query Analyzer
		The way that a statement can be physically executed is called an execution plan or a query plan.
		This execution plan is basically a step for step instruction for how the statement must be executed.
		If you select this tab, the execution plan will be calculated and displayed.
	www.cachemonitor.de /cache-monitor/docu/the-execution-plan-in-query-analyzer.html (257 words)

	EXPLAIN(5)
		The execution plan shows how the table(s) referenced by the query will be scanned---by plain sequential scan, index scan, etc.---and if multiple tables are referenced, what join algorithms will be used to bring together the required tuples from each input table.
		The most critical part of the display is the estimated query execution cost, which is the planner's guess at how long it will take to run the query (measured in units of disk page fetches).
		For most queries the total time is what matters, but in contexts such as an EXISTS sub-query the planner will choose the smallest start-up time instead of the smallest total time (since the executor will stop after getting one tuple, anyway).
	h30097.www3.hp.com /docs/iass/OSIS_62/MAN/MAN5/0037____.HTM (440 words)

	Query optimization: articles and papers
		We consider the problem for views and workloads that consist of equality-selection, project and join queries, and show that the complexity of the problem depends crucially on the quality of the estimates that a query optimizer has on the size of the views it is considering to materialize.
		When a query optimizer has good estimates of the sizes of the views, we show that an optimal choice of views may involve a number of views that is exponential in the size of the database schema.
		It is shown how this optimization considerably improves the efficiency of evaluating SQL queries, especially queries that have query graphs with a large number of query blocks (which is a typical situation when queries are defined in terms of multiple views and sub-queries).
	www.sqlsummit.com /Optimization.htm (1021 words)

	The Tukwila Execution Interface (Site not responding. Last check: 2007-10-31)
		A request is simply a physical query plan in the format described later in this document.
		Once a query has been submitted to the execution system, it is expected that the optimizer will hold the socket open for the duration of query execution.
		Each plan and request will get a unique ID. The element also has an attribute for the current user ID to use, and for specifying the root of the entire query plan.
	data.cs.washington.edu /integration/tukwila/tukwila_query.html (1241 words)

	What exactly is a query plan (or a SQL plan for that matter)
		The plan is akin to you being told where in a book your answer is. If you are told it is on page 23, then you would probably "plan" the binary searching algorithm.
		If it had to recompile the plan each time the query was run and you ran this query several tims a second you would be losing significant CPU speed.
		Now if you only run this query a couple times an hour you are not going to benefit as much from having the plan cached.
	www.codecomments.com /message377227.html (1124 words)

	Query plan not using index for some reason. Free discussion
		Query plan not using index for some reason.
		The query is on two tables, both of which have indexes.
		EXPLAIN for the query without the OR clause the planner uses the index.
	www.qaix.com /postgresql-database-development/217-517-query-plan-not-using-index-for-some-reason-read.shtml (788 words)

	Why is Stored Proc plan slower than query plan
		The query is complex and has multiple sub-queries that contain aggregates so I assume that may be a contributing factor.
		I agree that the query plans should be the same.
		Apparently, the reasonn for the difference in query plan was caused by the non-standard handling of NULLs.
	www.mcse.ms /message306009.html (1948 words)

	SQL Server Query Execution Plan Analysis
		Once you run this command, any query you execute in this Query Analyzer sessions will not be run, but a text-based version of the query plan will be displayed.
		In very complex query plans, the plan is divided into many parts, with each part listed one on top of the other on the screen.
		This means you must scroll to the far right of the graphical query plan to see where each step starts.
	www.sql-server-performance.com /tips/query_execution_plan_analysis_p1.aspx (921 words)

	lab2
		Let Q1 be the POPULATION based query which retrieves a couple of tuples and Q2 be the POPULATION based query which retrieve most of the tuples.
		Explain why the index on population is not always used for range queries based on population attribute.
		Derive an algebric condition on the selectivity of range query in terms of record size, block size, key-value size, pointer value size and depth of secondary index to quantify your arguement.
	www-users.cs.umn.edu /~shekhar/5708/labs/lab2.html (899 words)

	[No title] (Site not responding. Last check: 2007-10-31)
		Query optimizer here traverses from leftmost z = 02159 to rightmost z = 04158 and uses h = 'c' and inc = 10 as screening predicates.
		A plan to execute a query where at least one indexable predicate must match the first column of an index (known as matching predicate, matching index).
		In-list is special because it is considered a sequence of equal matching predicates that the query optimizer agrees to bridge in the access plan C1 in (6, 8, 10) and C2 = 5 and C3 = 20 is like C1 = 6 and.
	www.cs.umb.edu /~poneil/dbppp/notes/chap9.doc (3862 words)

	PRB: Access Violation Exception Occurs When Optimized Query Plan Uses Hash Match Team Operator (Site not responding. Last check: 2007-10-31)
		If the query plan uses Hash Team operators during query optimization, an access violation exception may occur in a SELECT statement.
		If the query performs a grouping operation with one or more joins on the same set of columns.
		If you have a query that fails with an access violation exception, verify the query plan to determine if a Hash Match Team operator is involved.
	support.microsoft.com /default.aspx?scid=kb;en-us;818671 (498 words)

	Execution Plan Caching and Reuse
		The algorithms to match new SQL statements to existing, unused execution plans in the cache require that all object references be fully qualified.
		Each query plan and execution context has an associated cost factor that indicates how expensive the structure is to compile.
		The age of our sample query plan is decremented to 0 after 16 scans of the procedure cache, unless another user references the plan.
	msdn.microsoft.com /library/default.asp?url=/library/en-us/architec/8_ar_sa_4azp.asp (972 words)

	Analysing a query-plan
		You suspect an index is being ignored or you are missing an index on a particular column.
		The EXPLAIN command displays the query plan that Postgres uses.
		Complex queries produce complex query plans - pay careful attention to the rows part.
	www.archonet.com /pgdocs/query-plan.html (201 words)

	Query Plan
		Priodata Query Plan is a front-end to the most commonly used V$ views to investigate SQL execution performance in the Oracle Database.
		Query Plan really improves performance of the process of tuning Oracle applications.
		This product is ideal for consultants, DBAs and also application developers, because it automates some queries one must write in order to do a proper tuning of the database.
	www.list32.com /program_Query_Plan_11.htm (302 words)

	[No title]
		A: (4) Many others, especially with aggregates * Since rewrites are not guaranteed to be improvements, could generate alternatives and send all of them to physical query plan generator.
		A: Exercise: Consider physical plan to execute (R NLJ S NLJ T) with no indexes and print the result.
		Query shapes and hash joins --------------------------- Consider hash join with "build" on left and "probe" on right: Algorithm: 1.
	www-db.stanford.edu /~ullman/dbsi/win99-346/query2.txt (462 words)

	dBforums - dropping constraint changes query plan
		analyzying an execution plan for a long-running query, we were able to force the
		thought that it was a good plan, which it wasn't.
		Otherwise post the query and plan and we'd be able to give you better answer.
	www.dbforums.com /t407098.html (866 words)

	Microsoft SQL Server: SQL Query Plan
		We have a couple of queries on our servers that when a specific parameter is passed is queried on the query will go into a state of hanging the server for ever.
		One of the queries is something like give me the invoices for a customer where the salesman is a specific number.
		When I use 47 on the query the query will display that it is going do some sort of parrallelism, when I run the query with any other number it doesn't do that.
	www.experts-exchange.com /Databases/Microsoft_SQL_Server/Q_20330539.html (353 words)

	The 5-A-Day Query Plan By Christina Spence-Maharajh
		And, just as you occasionally miss a multivitamin, you may have days when you just can't send out any queries.
		If your handshake is wimpy - a poorly written query letter - their first impression will be a negative one.
		My husband has a saying that I just love - "Don't talk the talk, if you can't walk the walk." Meaning that it's far easier to plan, prepare and talk about all of your plans of becoming a hugely successful freelance writer, than it is to sit down and really accomplish it.
	www.writersweekly.com /articles/122601-01.html (819 words)

	iAnywhere.com - QUERY_PLAN_ON_OPEN option [compatibility] (Site not responding. Last check: 2007-10-31)
		Controls whether a plan is returned when a cursor is opened.
		In early versions of the software, each time an OPEN was done on a cursor, the server would return in the SQLCA sqlerrmc field a string representing the query plan (limited to 70 bytes).
		For this reason, computing and returning the query plan on an OPEN is needed only for compatibility with old applications.
	www.ianywhere.com /developer/product_manuals/sqlanywhere/0901/en/html/dbdaen9/00000727.htm (107 words)

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