
	Where results make sense

Topic: Query optimizer

Related Topics

SQL

In the News (Sat 26 Dec 09)

Northern Trust

Marvin Harrison

Peter Chernin

Gary Locke

Match Play

Penelope Cruz

Mickey Rourke

AR Rahman

Danny Boyle

Hugh Jackman

	Query optimizer - Wikipedia, the free encyclopedia
		The query optimizer is the component of a database management system that attempts to determine the most efficient way to execute a query.
		The optimizer considers the possible query plans for a given input query, and attempts to determine which of those plans will be the most efficient.
		In this manner, a query plan is eventually produced that joins all the queries in the relation.
	en.wikipedia.org /wiki/Query_optimizer (685 words)

	Query plan - Wikipedia, the free encyclopedia
		A query plan (or query execution plan) is an 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 some of the different, correct possible plans for executing the query and returns what it considers the best alternative.
		In some databases the query plan can be reviewed, problems found, and then the query optimizer given hints on how to improve it.
	en.wikipedia.org /wiki/Query_plan (623 words)

	Microsoft SQL Server 7.0 Query Processor (Microsoft SQL Server 7 Technical Articles) (Site not responding. Last check: 2007-11-04)
		Query optimization is the process of choosing the fastest execution plan.
		Query execution is the process of executing the plan chosen during query optimization.
		A syntax-based query optimizer creates a procedural plan for obtaining the answer to a SQL query, but the particular plan it chooses is dependent on the exact syntax of the query and the order of clauses within the query.
	msdn.microsoft.com /library/techart/queryproc.htm (7386 words)

	SQL - Wikipedia, the free encyclopedia (via CobWeb/3.1 planetlab2.georgetown.edu) (Site not responding. Last check: 2007-11-04)
		Structured English Query Language ("SEQUEL") was designed to manipulate and retrieve data stored in System R. The acronym SEQUEL was later condensed to SQL because the word 'SEQUEL' was held as a trademark by the Hawker-Siddeley aircraft company of the UK.
		However, it also makes it possible for SQL source code to be produced (and optimized) by software, leading to the development of a number of natural language database query languages, as well as 'drag and drop' database programming packages with 'object oriented' interfaces.
		Translating the query into an efficient query plan is left to the database system, more specifically to the query optimizer.
	en.wikipedia.org.cob-web.org:8888 /wiki/SQL (2300 words)

	SQL Anywhere Cost Based Query Optimizer - Sybase Inc
		Over time, as the optimizer learns more about the characteristics of the data in the database, the SQL Anywhere optimizer may choose a different access plan for execution because its estimates are more exact (see Section 4.2) or because the data distribution has changed due to update operations.
		After the first query has run, and all the rows in the result have been retrieved, the SQL Anywhere optimizer analyzes its processing in an effort to learn about the characteristics of the `state' column in the employee table.
		If the optimizer needs to estimate the selectivity of a predicate that includes a non-indexed column for which no prior statistics are available, it estimates the number of records satisfying the selection condition using a set of default selectivity estimates based on a uniform distribution of random data.
	www.sybase.com /detail?id=1003010 (4414 words)

	14 The Query Optimizer
		To specify the goal of the query optimizer for an individual SQL statement, use one of the hints in Table 14-3.
		The query optimizer determines which execution plan is most efficient by considering available access paths and by factoring in information based on statistics for the schema objects (tables or indexes) accessed by the SQL statement.
		The optimizer estimates the cost of each plan based on statistics in the data dictionary for the data distribution and storage characteristics of the tables, indexes, and partitions accessed by the statement.
	www.stanford.edu /dept/itss/docs/oracle/10g/server.101/b10752/optimops.htm (9784 words)

	Columbia Query Optimizer
		The Columbia Query Optimization Project is a joint research project of David Maier from the Oregon Graduate Institute and Leonard Shapiro from Portland State University.
		Since the behaviour of the optimizer is complicated, it is difficult to debug or verify the process of optimization.
		In query optimization, the problem is to find the cheapest plan for a given query, subject to a certain context.
	web.cecs.pdx.edu /~len/Columbia (2701 words)

	LEO: An autonomic query optimizer for DB2
		By monitoring queries as they execute, the autonomic optimizer compares the optimizer's estimates with actual cardinalities at each step in a QEP, and computes adjustments to its estimates that may be used during future optimizations of similar queries.
		Despite this, the optimizer assumes that the statistics reflect the current state of the database, that is, that the database characteristics are relatively stable, and it relies upon the user to know when any table has changed enough to warrant the expensive recollection of statistics.
		Feedback gives the greatest improvement to the modeling of queries that are either repetitive or are similar to earlier queries, that is, queries for which the optimizer's model exploits the same statistical information.
	www.research.ibm.com /journal/sj/421/markl.html (4670 words)

	Information about query performance in an Access database
		This means that the Optimizer assigns a time cost to each query task and then chooses the least expensive list of tasks to perform that generates the intended result set.
		A query is flagged for compiling when you save any changes to the query (or its underlying tables) and when the database is compacted.
		Because the query performance analysis is closely tied to the Jet database engine, the Performance Analyzer suggests adding indexes only when the indexes will actually be used by the Jet database engine to optimize the query.
	support.microsoft.com /?kbid=209126 (1954 words)

	Query Optimization > The MySQL Query Optimizer
		The MySQL query optimizer has several goals, but its primary aims are to use indexes whenever possible and to use the most restrictive index in order to eliminate as many rows as possible as soon as possible.
		The optimizer will also do a quick check of the index to estimate how many entries will be used when determining whether the index should be used for constant comparisons.
		If you run a query only once each of two different ways, you'll often find that the second query is faster just because information from the first query is still cached and need not actually be read from the disk.
	www.samspublishing.com /articles/article.asp?p=377069&seqNum=2&rl=1 (3231 words)

	Sql server query optimizer (Site not responding. Last check: 2007-11-04)
		The disadvantage was that the optimizer did not take this reduction into account during the query optimization phase.
		With the release of SQL Server 7.0, views were combined with constraints to allow the query optimizer to remove irrelevant tables from the query plan (ie...
		Query hints, on the other hand, are more of a directive rather than a suggestion.
	5860.m9dsfb.info (751 words)

	Analytical and Empirical Tools for Advanced Query Optimizer Engineering
		Optimizers are hard to build because for any given query, there can be a prohibitively large number of plans to choose from.
		Typically, the complexity of optimization is handled by dividing optimization into two phases: a heuristic phase (called query rewriting) that narrows the space of plans to consider, and a cost-based phase that compares the relative merits of plans that lie in the narrowed space.
		Typically, the goal of such extensions is to reuse the relational query optimizer as much as possible, both to save in development costs and to exploit the maturity of relational optimizer technology.
	www.cs.ucla.edu /csd/IDM99/Proceedings/Summaries/Zdonik.htm (1235 words)

	Query Optimization > Using Indexing (Site not responding. Last check: 2007-11-04)
		Those are the kinds of issues that this chapter focuses on, with the goal of assisting you in optimizing the performance of your database system so that it processes your queries as quickly as possible.
		In a single-table query, the number of values you need to examine per column is the number of rows in the table.
		Under these circumstances, the index might never be used at all, because the query optimizer generally skips an index in favor of a full table scan if it determines that a value occurs in a large percentage of a table's rows.
	www.samspublishing.com /articles/article.asp?p=377069&seqNum=2&rl=1 (3717 words)

	MySQL 5.0 Reference Manual :: 7.5.3 Controlling Query Optimizer Performance
		The task of the query optimizer is to find an optimal plan for executing an SQL query.
		However, when larger queries are submitted, the time spent in query optimization may easily become the major bottleneck in the server's performance.
		The general idea is that the fewer plans that are investigated by the optimizer, the less time it spends in compiling a query.
	dev.mysql.com /doc/refman/5.0/en/controlling-optimizer.html (532 words)

	Teradata Magazine \| It's in the data: Why collecting statistics will make the most of your system...
		If there are multiple tables to be joined in a query, the optimizer can produce better join plans if you have PI statistics for each table.
		The reason for this is that when there are no statistics on a skewed column, the optimizer chooses to take a conservative course by assuming that a certain percentage of the data values will qualify for the query.
		In conclusion, the more statistics available to the Teradata optimizer, and the more accurate and up-to-date those statistics are, the better able the optimizer will be to select the most efficient access methods for retrieving data.
	www.teradata.com /t/page/115444 (1341 words)

	K2 - Query Optimizer (Site not responding. Last check: 2007-11-04)
		K2 has a flexible, extensible query optimizer which uses both rewrite rules and a cost model.
		After a query has been translated into an abstract syntax tree, which K2 uses to represent queries internally, it is manipulated by applying a series of rewrite rules.
		First, a collection of rules is applied which simplifies the query, by taking pieces expressed using certain kinds of tree nodes and replacing them with others.
	db.cis.upenn.edu /K2/optimizer.html (315 words)

	Genetic Query Optimizer
		The number of alternative plans to answer a query grows exponentially with the number of joins included in it.
		Further optimization effort is caused by the support of a variety of
		Performance difficulties in exploring the space of possible query plans created the demand for a new optimization technique to be developed.
	jamesthornton.com /postgres/7.4/geqo.html (260 words)

	Query Optimizer (Site not responding. Last check: 2007-11-04)
		The optimizer is in general a System R style optimizer, as described in "Access Path Selection in a Relational Database Management System", Proceedings of the ACM-SIGMOD International Conference on Management of Data, June 1979.
		See the text for a more detailed description of query optimization and the associated cost formulas.
		Note that the optimizer may have had some changes since these plans were generated, so your results may not be identical.
	www.cs.wisc.edu /~dbbook/openAccess/Minibase/optimizer/optimizer.html (222 words)

	A Region Based Query Optimizer Through Cascades Query Optimizer Framework - Ozcan, Nural, Koksal, Altinel, Dogac ...
		Abstract: The Cascades Query Optimizer Framework is a tool to help the database implementor (DBI) in constructing a query optimizer for a DBMS.
		It is data model independent and allows to code a query optimizer by providing the implementations of the subclasses of predefined interface classes.
		When the implementations of the required classes are provided properly, the generated optimizer produces the optimum execution plans for the queries.
	citeseer.ist.psu.edu /245905.html (445 words)

	Web Query Optimizer - Zadorozhny (ResearchIndex)
		Abstract: We demonstrate a Web Query Optimizer (WQO) within an architecture of mediators and wrappers, for WebSources of limited capability in a wide area environment.
		The WQO has several innovative features including a CBR (capability based rewriting) Tool, an enhanced randomized relational optimizer extended to a Web environment, and a WebWrapper cost model that can provide relevant metrics for accessing WebSources.
		Efficient Evaluation of Queries in a Mediator for..
	citeseer.ist.psu.edu /417160.html (381 words)

	EDB631: Performance and Tuning: Adaptive Server Enterprise Query Optimizer - Sybase Inc
		Study various techniques for writing high-performance queries that allow the optimizer to use the most efficient query plan, and learn how to diagnose and correct performance problems with existing queries.
		Gain proficiency in interpreting and modifying optimizer statistics to improve query performance and using simulated statistics for “what if” analysis.
		The Adaptive Server Query Optimizer, showplan and other Sybase utilities, optimizing joins, optimizer statistics, abstract plans, tuning insert, update, and delete operations, parallel query plans, using indexes to reduce I/O, and Stored Procedures.
	www.sybase.com /detail?id=1017141 (239 words)

	References for Columbia Query Optimizer
		Keith Billings, A TPCD Model for Database Query Optimization in Cascades, M.S. Thesis, Portland State University, Spring 1997.
		Gassner, G. Lohman and K. Schiefer, Query Optimization in IBM's DB2 Family of DBMSs, IEEE Data Engineering Bulletin, 16(4), December 1993.
		Ono and G. Lohman, Measuring the Complexity of Join Enumeration in Query Optimization, Proc.
	www.cs.pdx.edu /~len/Columbia/References.html (475 words)

	query optimizer (Site not responding. Last check: 2007-11-04)
		I got this simple dynamic query - just a select...where using the exact
		My guess is the query optimizer decides to change the execution plan because
		By the way, total db size is about 60 GB+ now, the table size is near 15 GB.
	www.lazydba.com /sql/1__6325.html (106 words)

Try your search on: Qwika (all wikis)