CN103218439A - Virtual attribute query optimization method of object-oriented proxy database - Google Patents
Virtual attribute query optimization method of object-oriented proxy database Download PDFInfo
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Abstract
The invention discloses a virtual attribute query optimization method of an object-oriented proxy database. According to the method, an optimization scheme based on expression upgrading is proposed. In the optimization scheme based on the expression upgrading, a cost estimating function is proposed after cost estimation is carried out on query of source classes corresponding to different proxy classes according to distinct characteristics of the proxy classes. Scanning cost of the source classes and the proxy classes can be well measured by means of the cost estimating function, and further the fact that whether to carry out the expression upgrading or not is determined. After requirements are met, query of the proxy classes is upgraded to query of the source classes by means of a processing mode similar to a view processing mode, and therefore the number of times of expression changing-over calculation is reduced and the purpose of optimization is achieved. The practicality of the object-oriented proxy database can be greatly improved by means of the optimization of virtual attribute query.
Description
Technical field
The present invention relates to the data base querying process field, especially relate to a kind of empty attribute query optimization method of object-oriented proxy database.
Background technology
Along with the development of infotech, database technology is also progressive constantly.The traditional database that with the relevant database is representative is because of its complete theory and effective implementation method, obtained significant progress and extensively effectively uses.New field such as Geographic Information System, knowledge base system and multimedia information system etc. have proposed new demand to database, need efficiently to handle complex data type.It is the important directions of database technology research and application that database technology combines with object-oriented method, object oriented programming model occurred thereupon, has introduced key concepts such as object and object identity.In OODBS, database is an object set, and object is made up of data and method.
OODBS is supported unconventional data type preferably, but lacks common model and formalized description, and the degree of ripeness deficiency is difficult to use and promote in reality technically.As the expansion of object oriented programming model, the object broker model derives from procuratorial notion in the life.In the object broker model, the processing of object information mainly is to construct an agent object as its view, and agent object can be inherited the part or all of attribute of source object, is called empty attribute, also can expand new attribute simultaneously, is called real attribute.All objects of sharing same attribute and method constitute an object class, and all agent objects constitute proxy class.In actual storage, only store the value of real attribute, an empty attribute memory module information, its value of actual storage not, but obtain the value of corresponding real attribute by pointer.
Object broker database according to the object broker model is realized because of its special memory mechanism, adopts the mode of switching expression formula, stores the related of empty attribute and real attribute, by this evaluation of expression being obtained in real time the value of empty attribute.In the object broker data base querying execute phase, empty attribute obtain the very big efficient that has influenced inquiry, optimize the promoted the use of significant meaning of the search efficiency of empty attribute for the object broker database.
Summary of the invention
Above-mentioned technical matters of the present invention is mainly solved by following technical proposals:
A kind of empty attribute query optimization method of object-oriented proxy database is characterized in that, based on to give a definition: in the object broker database, proxy class is similar to special view, but the view of identity relation type database not; Proxy class can be inherited the attribute and the method for source class, can expand corresponding attribute again simultaneously; During inquiry on handling proxy class, can use for reference the method that relevant database is handled view, the query expression that is about on the proxy class rises on the class of source, and this process is referred to as expression formula and promotes; When creating proxy class, agent rule partly need be extracted, agent rule is identical with the form of creating view, adopts the mode of system creation view, and the form of proxy class with view is registered in the system; Described expression formula promotes and may further comprise the steps:
Step 1 is set up proxy class tabulation DeputyList, and the scope tabular table that scan for inquiries relates to judges whether current class is proxy class, if current class is a proxy class, and does not relate to such real attribute in inquiry, then joins among the DeputyList; If current class is not a proxy class, then need not to carry out expression formula and promote, finish whole steps;
Step 2, for each proxy class among the DeputyList that generates in the step 1, the cost that establishing its inquiry needs is cost1, and the inquiry cost of establishing simultaneously on the corresponding source class in proxy class lifting back is cost2, if cost1〉cost2, then this proxy class of mark is for promoting; If cost1＜=cost2, the cost that then promotes after the expression formula is not less than the cost that does not promote, and this proxy class of mark is not for promoting;
Step 3 for being labeled as the proxy class that can promote among the DeputyList, adopts the mode of query rewrite, and the place that this proxy class is occurred rewrites, and comes rewritten query with source class and agent rule, thereby realizes that expression formula promotes;
Step 4, query expression is promoted to the source class after, if this source class is a proxy class, go to step 2.If this source class is not a proxy class, then finish whole process.
At the empty attribute query optimization method of above-mentioned a kind of object-oriented proxy database, in the described step 2, in step 2, cost computation process is as follows:
The object broker model is by object broker algebra definition proxy class; Object broker algebraically mainly is made of SELECT, PROJECT, EXTEND, UNION, six kinds of basic operations of JOIN, GROUP, combination according to these six kinds of basic operations, four kinds of basic proxy class types in the object broker database, have been defined, be respectively four kinds of SELECT, UNION, JOIN, GROUP, because in the object broker database, index scanning has singularity, and in order to combine with traditional database, the spy introduces the cost under the sequential scanning;
Step 2.1, proxy class has adopted storage real attribute value when storage, and empty attribute is only stored the strategy of source object and agent object bidirectional pointer.When the scanning proxy class, can not directly obtain the value of empty attribute.The cost of obtaining empty property value is divided into the scanning proxy class, search source object and agent object bidirectional pointer table (pg_bipointer) and obtain source object three parts according to the source object object identity, and it is expressed shown in formula one:
PCost=N (D)+MAPCost+PF (S) formula one
Wherein, definition N (D) is the shared disk number of proxy class D, and MAPCost is the cost of scanning pg_bipointer table, and PF (S) is for obtaining the cost of source object.
Step 2.2, in the SELECT proxy class, the inquiry on the proxy class risen to the source class after, the cost that scanning relates to is mainly the cost of scan source table, it is expressed shown in formula two:
FCost1=N (S) formula two
Wherein, definition N (S) is the shared disk number of source class S.
Step 2.3, in the UNION proxy class, the inquiry on the proxy class risen to the source class after, must realize the UNION operation of two subqueries during scanning, therefore the cost after promoting is mainly the cost of two subqueries and UNION operation, and it is expressed shown in formula three:
FCost2=N (S1)+N (S2)+P (S1)+P (S2) formula three
Wherein, definition N (S1)=shared disk number of source class S1, N (S2) is the shared disk number of source class S2, and P (S1) is a source class S1 number of tuples, and P (S2) is a source class S2 number of tuples.
Step 2.4, in the JOIN proxy class, the inquiry on the proxy class risen to the source class after, must realize the JOIN operation of class during scanning, and JOIN to operate in the database be operation very consuming time, when this proxy class occurring, generally do not promote operation.It carries out cost formula after expression formula promotes shown in formula four:
FCost3=N (S1)+N (S2)+P (S1) * P (S2) formula four
Wherein, definition N (S1)=shared disk number of source class S1, N (S2) is the shared disk number of source class S2, and P (S1) is a source class S1 number of tuples, and P (S2) is a source class S2 number of tuples.
Step 2.5, in the GROUP proxy class, the inquiry on the proxy class risen to the source class after, need carry out aggregation operator during inquiry, but no matter whether promote, all need to carry out aggregation operator during inquiry.Therefore after promoting expression formula, carry out cost when calculating, mainly consider that its cost formula is shown in formula five to the scanning of source class and the source class cost by certain property groupings:
FCost4=N (S)+V (S1) formula five
Wherein, definition N (S) is the shared disk number of source class S, and V (S1) is the cost of source class S by certain property groupings.
Step 2.6 compares PCost and FCost, if PCost is bigger, then promotes the expression formula operation.
Therefore, the present invention has following advantage: 1. for the inquiry effect of having greatly improved of proxy class, specify as follows: at the characteristics and the situation of different proxy class, adopt the mode of cost estimated, expression formula is promoted front and back carry out cost calculating respectively, the proxy class that selection satisfies condition promotes, thereby guarantees that the efficient that expression formula promotes inquiry has castering action; 2. realize having very big directive function for system, specify as follows: at the characteristics of proxy class, during the definition agent rule, adopt the processing mode of view in the traditional database, in lifting process, proxy class is carried out query rewrite, for the inquiry of proxy class provides a mode more efficiently; 3. time complexity is low, and the search efficiency of object broker database is had bigger raising, for the popularization of object broker database great meaning is arranged.
Description of drawings
Fig. 1 is proxy class definition form.
Fig. 2 is the agent rule form of SELECT proxy class.
Fig. 3 is a method flow synoptic diagram of the present invention.
Embodiment
Below by embodiment, and in conjunction with the accompanying drawings, technical scheme of the present invention is described in further detail.
Embodiment:
The present invention is to provide the search efficiency that improves empty attribute based on the mode that promotes expression formula, specifically is to adopt the method that may further comprise the steps:
In the object broker database, proxy class is similar to special view, but the view of identity relation type database not.Proxy class can derived class attribute and method, can expand corresponding attribute again simultaneously.During inquiry on handling proxy class, can use for reference the method that relevant database is handled view, the query expression that is about on the proxy class rises on the class of source, and this process is referred to as expression formula and promotes.When creating proxy class, proxy class definition form as shown in Figure 1, agent rule partly need be extracted, with the SELECT proxy class is example, as shown in Figure 2, agent rule is identical with the form of creating view, adopts the mode of system creation view, and the form of proxy class with view is registered in the system.
The step that promotes expression formula comprises following substep:
Step 1 is set up proxy class tabulation DeputyList, and the scope tabular table that scan for inquiries relates to judges whether current class is proxy class, if current class is a proxy class, and does not relate to such real attribute in inquiry, then joins among the DeputyList.If current class is not a proxy class, then need not to carry out expression formula and promote.
Step 2, for each proxy class among the DeputyList, the cost cost1 that inquiry needs directly transforms proxy class to inquiring about on the class of source, if the cost cost2 that inquiry needs is cost1〉cost2, then this proxy class of mark is for promoting.If cost1＜=cost2, the cost that then promotes after the expression formula is not less than the cost that does not promote, and this proxy class of mark is not for promoting.
Step 3 for being labeled as the proxy class that can promote among the DeputyList, adopts the mode of query rewrite, and the place that this proxy class is occurred rewrites, and comes rewritten query with source class and agent rule, thereby realizes that expression formula promotes.
Step 4, query expression is promoted to the source class after, if this source class is a proxy class, go to step 2.If this source class is not a proxy class, then finish whole process.
Cost estimated part in the step 2 is elaborated with a concrete example:
The SELECT proxy class is only to allow to select from a class source object to act on behalf of.Source object and agent object are one to one.With an instantiation boosting algorithm is described.
CREATE CLASS basicA (a int, b int, c int); Index is arranged on a
CREATE?SELECTDEPUTYCLASS?deputyB(d?int)?as?(select?a+2?as?newa,?b?from?basicA?where?a?>3?and?b?>4);
Query statement: SELECT newa, b FROM deputyB WHERE newa＜10;
In the query compiler stage, comprise proxy class deputyB in the object table.Carry out cost estimation now, judge whether to carry out expression formula and promote.
The direct cost that deputyB is scanned: scanning pattern is divided into sequential scanning and tape index scanning, and cost is respectively cost1, and cost2 selects the less scanning pattern cost3=min(cost1 of cost, cost2).Owing to comprise empty attribute in the alternative condition, therefore can switch expression formula and calculate, cost comprises the inquiry of system's table and the I/O operation of getting real attribute, is designated as cost4.Wherein, less can the ignoring of CPU cost of expression solution symbol.When the objective attribute target attribute row comprised empty attribute, similar with the processing procedure that comprises empty attribute in the alternative condition, cost was cost5.Total cost sumcost1=cost3+cost4+cost5.
Be converted into the cost that basicA scans: index is arranged on a, scanning that may the select tape index, path that also may selecting sequence scanning, cost is respectively cost6 and cost7, and the scanning cost is cost8=min(cost6, cost7).When condition judgment and project, because the value of tuple is real attribute, be in esse, only relate to the CPU cost.Total cost sumcost2=cost8.
Query rewrite part in the step 3 is elaborated with a concrete example:
As sumcost1＜sumcost2, expression formula is risen on the class of source, use for reference the PostgreSQL database to the process that view query rewrites, be converted into:
Original query tree after analyzed device is explained, expression mode in logic:
SELECT?deputyB.newa,?deputyB.b?FROM?deputyB?WHERE?deputyB.newa<10;
Query tree after expression formula promotes, expression mode in logic:
SELECT?deputyB.newa,?deputyB.b?FROM?(SELECT?a+2?as?newa,?b?FROM?basicA?where?a>3?and?b>4)?deputyB?WHERE?deputyB.newa?<?10;
Inquiry on the deputyB is converted into inquiry to basicA.
Its excess-three kind proxy class situation and SELECT proxy class situation are similar, can be with reference to the processing mode of SELECT.
Specific embodiment described herein only is that the present invention's spirit is illustrated.The technician of the technical field of the invention can make various modifications or replenishes or adopt similar mode to substitute described specific embodiment, but can't depart from spirit of the present invention or surmount the defined scope of appended claims.
Claims (2)
1. the empty attribute query optimization method of an object-oriented proxy database is characterized in that, based on to give a definition: in the object broker database, proxy class is similar to special view, but the view of identity relation type database not; Proxy class can be inherited the attribute and the method for source class, can expand corresponding attribute again simultaneously; During inquiry on handling proxy class, can use for reference the method that relevant database is handled view, the query expression that is about on the proxy class rises on the class of source, and this process is referred to as expression formula and promotes; When creating proxy class, agent rule partly need be extracted, agent rule is identical with the form of creating view, adopts the mode of system creation view, and the form of proxy class with view is registered in the system; Described expression formula promotes and may further comprise the steps:
Step 1 is set up proxy class tabulation DeputyList, and the scope tabular table that scan for inquiries relates to judges whether current class is proxy class, if current class is a proxy class, and does not relate to such real attribute in inquiry, then joins among the DeputyList; If current class is not a proxy class, then need not to carry out expression formula and promote, finish whole steps;
Step 2, for each proxy class among the DeputyList that generates in the step 1, the cost that establishing its inquiry needs is cost1, and the inquiry cost of establishing simultaneously on the corresponding source class in proxy class lifting back is cost2, if cost1〉cost2, then this proxy class of mark is for promoting; If cost1＜=cost2, the cost that then promotes after the expression formula is not less than the cost that does not promote, and this proxy class of mark is not for promoting;
Step 3 for being labeled as the proxy class that can promote among the DeputyList, adopts the mode of query rewrite, and the place that this proxy class is occurred rewrites, and comes rewritten query with source class and agent rule, thereby realizes that expression formula promotes;
Step 4, query expression is promoted to the source class after, if this source class is a proxy class, go to step 2, if this source class is not a proxy class, then finish whole process.
2. according to claim 1, it is characterized in that in the described step 2, in step 2, cost computation process is as follows:
The object broker model is by object broker algebra definition proxy class; Object broker algebraically mainly is made of SELECT, PROJECT, EXTEND, UNION, six kinds of basic operations of JOIN, GROUP, combination according to these six kinds of basic operations, four kinds of basic proxy class types in the object broker database, have been defined, be respectively four kinds of SELECT, UNION, JOIN, GROUP, because in the object broker database, index scanning has singularity, and in order to combine with traditional database, the spy introduces the cost under the sequential scanning;
Step 2.1, proxy class is when storage, adopted storage real attribute value, empty attribute is only stored the strategy of source object and agent object bidirectional pointer, when the scanning proxy class, can not directly obtain the value of empty attribute, the cost of obtaining empty property value is divided into the scanning proxy class, search source object and agent object bidirectional pointer table (pg_bipointer) and obtain source object three parts according to the source object object identity, and it is expressed shown in formula one:
PCost=N (D)+MAPCost+PF (S) formula one
Wherein, definition N (D) is the shared disk number of proxy class D, and MAPCost is the cost of scanning pg_bipointer table, and PF (S) is for obtaining the cost of source object;
Step 2.2, in the SELECT proxy class, the inquiry on the proxy class risen to the source class after, the cost that scanning relates to is mainly the cost of scan source table, it is expressed shown in formula two:
FCost1=N (S) formula two
Wherein, definition N (S) is the shared disk number of source class S;
Step 2.3, in the UNION proxy class, the inquiry on the proxy class risen to the source class after, must realize the UNION operation of two subqueries during scanning, therefore the cost after promoting is mainly the cost of two subqueries and UNION operation, and it is expressed shown in formula three:
FCost2=N (S1)+N (S2)+P (S1)+P (S2) formula three
Wherein, definition N (S1)=shared disk number of source class S1, N (S2) is the shared disk number of source class S2, and P (S1) is a source class S1 number of tuples, and P (S2) is a source class S2 number of tuples;
Step 2.4, in the JOIN proxy class, after inquiry on the proxy class risen to the source class, must realize the JOIN operation of class during scanning, and JOIN to operate in the database be operation very consuming time, when this proxy class occurring, generally do not promote operation, it carries out cost formula after expression formula promotes shown in formula four:
FCost3=N (S1)+N (S2)+P (S1) * P (S2) formula four
Wherein, definition N (S1)=shared disk number of source class S1, N (S2) is the shared disk number of source class S2, and P (S1) is a source class S1 number of tuples, and P (S2) is a source class S2 number of tuples;
Step 2.5, in the GROUP proxy class, after inquiry on the proxy class risen to the source class, need carry out aggregation operator during inquiry, but no matter whether promote, all need to carry out aggregation operator during inquiry, when therefore after promoting expression formula, carrying out cost calculating, the cost that main consideration is pressed certain property groupings to the scanning and the source class of source class, its cost formula is shown in formula five:
FCost4=N (S)+V (S1) formula five
Wherein, definition N (S) is the shared disk number of source class S, and V (S1) is the cost of source class S by certain property groupings;
Step 2.6 compares PCost and FCost, if PCost is bigger, then promotes the expression formula operation.
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| CN111797114A (en) * | 2020-06-24 | 2020-10-20 | 武汉大学 | Multi-path cross-class query and optimization method in object proxy database |
| CN112380192A (en) * | 2020-12-03 | 2021-02-19 | 广州海量数据库技术有限公司 | Method and system for realizing object-oriented framework in database |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN107480199A (en) * | 2017-07-17 | 2017-12-15 | 深圳先进技术研究院 | Query Reconstruction method, apparatus, equipment and the storage medium of database |
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| CN110162642A (en) * | 2019-05-21 | 2019-08-23 | 武汉大学 | Patent knowledge map construction method based on object broker database |
| CN111797114A (en) * | 2020-06-24 | 2020-10-20 | 武汉大学 | Multi-path cross-class query and optimization method in object proxy database |
| CN111797114B (en) * | 2020-06-24 | 2021-08-31 | 武汉大学 | Multi-path cross-class query and optimization method in object proxy database |
| CN112380192A (en) * | 2020-12-03 | 2021-02-19 | 广州海量数据库技术有限公司 | Method and system for realizing object-oriented framework in database |
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