摘要:
A method for determining the sensitivity of the fatigue life of a structural component with respect to specific design parameters includes obtaining the stress profile for a structural component under random process establishing a relationship between the stress profile and the fatigue life of the structural component, developing the sensitivity of the fatigue life with respect to design parameters, optimizing the design of the structural component based upon the design parameters to which the fatigue life is most sensitive.
摘要:
Under a type of query transformation referred to herein as join factorization, the branches of an UNION/UNION ALL query that join a common table are combined to reduce accesses to the common table. The transformation can be expressed as (T1 join T2) union all (T1 join T3)=T1 join (T2 union all T3), where T1, T2 and T3 are three tables. A given query may be rewritten in many alternate ways using join factorization. Evaluating each alternative can be expensive. Therefore, the alternatives are generated and evaluated in a way that minimizes the cost of evaluating the alternatives.
摘要翻译:在这里称为连接因式分解的一种类型的查询变换中,加入公共表的UNION / UNION ALL查询的分支被组合以减少对公共表的访问。 转换可以表示为(T1连接T2)联合全部(T1连接T3)= T1连接(T2联合全T3),其中T1,T2和T3是三个表。 给定的查询可以使用连接因式分解以许多替代方式重写。 评估每个替代品可能是昂贵的。 因此,以最小化评估替代品的成本的方式生成和评估替代方案。
摘要:
A method and apparatus for merging synopses to determine a database statistic, e.g., a number of distinct values (NDV), is disclosed. The merging can be used to determine an initial database statistic or to perform incremental statistics maintenance. For example, each synopsis can pertain to a different partition, such that merging the synopses generates a global statistic. When performing incremental maintenance, only those synopses whose partitions have changed need to be updated. Each synopsis contains domain values that summarize the statistic. However, the synopses may initially contain domain values that are not compatible with each other. Prior to merging the synopses the domain values in each synopsis is made compatible with the domain values in the other synopses. The adjustment is made such that each synopsis represents the same range of domain values, in one embodiment. After “compatible synopses” are formed, the synopses are merged by taking the union of the compatible synopses.
摘要:
Approaches, techniques, and mechanisms are disclosed for maintaining a set of baseline query plans for a database command. Except in rare circumstances, a database server may only execute a command according to a baseline plan, even if the database server predicts that a different plan has a lower cost. The set of baseline plans are plans that, for one reason or another, have been determined to provide acceptable actual performance in at least one execution context. When the database server receives a request to execute a particular command, the database server, if possible, always executes the command according to the lowest predicted cost baseline plan. The database server may evolve the plan baseline to include additional plans by generating and testing new plans in response to new requests to execute the database command, or as part of a query optimization or tuning process.
摘要:
A method and apparatus for approximating a database statistic, such as the number of distinct values (NDV) is provided. To approximate the NDV for a portion of a table, a synopsis of distinct values is constructed. Each value in the portion is mapped to a domain of values. The mapping function is implemented with a uniform hash function, in one embodiment. If the resultant domain value does not exist in the synopsis, the domain value is added to the synopsis. If the synopsis reaches its capacity, a portion of the domain values are discarded from the synopsis. The statistic is approximated based on the number (N) of domain values in the synopsis and the portion of the domain that is represented in the synopsis relative to the size of the domain.
摘要:
Under a type of query transformation referred to herein as join factorization, the branches of an UNION/UNION ALL query that join a common table are combined to reduce accesses to the common table. The transformation can be expressed as (T1 join T2) union all (T1 join T3)=T1 join (T2 union all T3), where T1, T2 and T3 are three tables. A given query may be rewritten in many alternate ways using join factorization. Evaluating each alternative can be expensive. Therefore, the alternatives are generated and evaluated in a way that minimizes the cost of evaluating the alternatives.
摘要翻译:在这里称为连接因式分解的一种类型的查询变换中,加入公共表的UNION / UNION ALL查询的分支被组合以减少对公共表的访问。 转换可以表示为(T 1连接T 2)联合全部(T 1连接T 3)= T 1连接(T 2并联全部T 3),其中T 1,T 2和T 3是三个表。 给定的查询可以使用连接因式分解以许多替代方式重写。 评估每个替代品可能是昂贵的。 因此,以最小化评估替代品的成本的方式生成和评估替代方案。
摘要:
The present invention involves the creation of defined chromosomal deficiencies, inversions and duplications using Cre recombinase in ES cells transmitted into the mouse germ line. These chromosomal reconstructions can extend up to 3-4 cM. Chromosomal rearrangements are the major cause of inherited human disease and fetal loss. Additionally, translocations and deletions are recognized as major genetic changes that are causally involved in neoplasia. Chromosomal variants such as deletions and inversions are exploited commonly as genetic tools in organisms such as Drosophila. Mice with defined regions of segmental haploidy are useful for genetic screening and allow accurate models of human chromosomal diseases to be generated.
摘要:
The present invention involves the creation of defined chromosomal deficiencies, inversions and duplications using Cre recombinase in ES cells transmitted into the mouse germ line. These chromosomal reconstructions can extend up to 3-4 cM. Chromosomal rearrangements are the major cause of inherited human disease and fetal loss. Additionally, translocations and deletions are recognized as major genetic changes that are causally involved in neoplasia. Chromosomal variants such as deletions and inversions are exploited commonly as genetic tools in organisms such as Drosophila. Mice with defined regions of segmental haploidy are useful for genetic screening and allow accurate models of human chromosomal diseases to be generated.
摘要:
Approaches, techniques, and mechanisms are disclosed for maintaining a history of query plans executed for a database command, along with information related to each query plan. A database server receives a request to execute a particular command. The database server determines a plan for executing the particular command. The database server adds first information to a plan history associated with the particular command. The plan history comprises information related to a plurality of plans that have been generated for the particular command. The first information may include, for example, properties of the plan (including an outline of the plan) as well as statistics collected during execution of the plan. The database server may implement techniques for periodically refreshing information in a plan history. The database server may also implement techniques for purging old or less important plans.
摘要:
A method and apparatus for approximating a database statistic, such as the number of distinct values (NDV) is provided. To approximate the NDV for a portion of a table, a synopsis of distinct values is constructed. Each value in the portion is mapped to a domain of values. The mapping function is implemented with a uniform hash function, in one embodiment. If the resultant domain value does not exist in the synopsis, the domain value is added to the synopsis. If the synopsis reaches its capacity, a portion of the domain values are discarded from the synopsis. The statistic is approximated based on the number (N) of domain values in the synopsis and the portion of the domain that is represented in the synopsis relative to the size of the domain.