Patent Publication Number: US-8533159-B2

Title: Processing materialized tables in a multi-tenant application system

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application, claims priority under 35 U.S.C. §119(a) from Chinese Patent Application No. 201010244499.2, filed on Jul. 30, 2010, the contents of which are incorporated herein by reference. 
     TECHNICAL FIELD 
     The present invention relates to a multi-tenant application, particularly, to the management of a database in a multi-tenant application, and more particularly, to an apparatus for processing materialized tables in a multi-tenant application system. 
     BACKGROUND 
     A multi-tenant application system provides a multi-tenant application to users of software through multi-tenant (MT) technologies, i.e., running a single instance of a software application on a server of a service provider to provide software application services for a plurality of tenants (e.g., organizations like enterprises), thus reducing the costs of the development, deployment and operation of the software application. 
     A database is a systematic data organization for performing effective and reliable storage, retrieval and processing of the data. A database is composed of tables, in which there are rows of associated data. The access to and operation on the data are accomplished by a Structured Query Language (SQL) query. 
     A basic-database is a typical type of database, which includes business data, for example, a database store of daily sales data of a store, including commodities, sales volumes, sale prices and sale times. 
     Data analysis can be made according to the basic-database used by the SQL query. For example, calculating the total daily sales volume of each commodity from the perspective of the commodity; as time goes by, calculating the total monthly sales volume of each commodity, and calculating the total annual sales volume of each commodity. 
     In the context of the present invention, a basic-database is also called a basic-table BT. 
     A materialized view (MV), also called a materialized table, can be created from a basic-table. The materialized table is also a kind of table in a database, which can store intermediate data that is exported from the basic-table, e.g., the aforesaid total monthly sales volume of a commodity. The materialized table can be used to query, and by using the intermediate data in the materialized table, the amount of calculation required by the complex query can be reduced, and thus the query efficiency is improved. 
     In a massive multi-tenant application system, materialized tables are widely used to improve the efficiency of data query operations. In such a case, a plurality of tenants share one or more basic-tables as well as materialized tables corresponding to the basic-tables, and usually tenant identifiers are used in the basic-tables and the materialized tables to distinguish between the tenants to which the data belongs. 
     In the design of a materialized table in a database, the basic-table and the materialized table maintain data synchronization there between. When operations, such as addition, deletion and modification, are made to the basic-table, the materialized table can only be queried and retrieved from after refreshing and synchronization. During the process of refreshing and synchronization of the materialized table, the materialized table will be locked. At this time, a SQL query of the user cannot act on the materialized table. For example, when the sales volume of the commodity of a new day is added into the basic-table, the corresponding materialized table cannot be used, since the monthly sales volume of the commodity in the materialized table does not yet reflect the sales volume of the commodity of the newly-added day, and if the data in the materialized table is used, the result will be incorrect. After performing operations, such as addition, deletion, and modification, to the basic-table, the materialized table can only be used after its data is synchronized with the data of the modified basic-table. For example, according to the modified basic-table, a materialized table is exported or generated again so that the total monthly sales volume of the commodity of the materialized table includes the total sales volume of the newly-added day. 
     In a multi-tenant application system using materialized tables, different tenants may have different update patterns for a shared basic-table, e.g., performing update operations of data addition, deletion or modification on the basic-table at different times and/or in different frequencies. If there are many tenants sharing the basic-table and the materialized table, then at any time, there may be tenants performing update operations on the common one or more shared basic-tables. Since a materialized table corresponds to a plurality of basic-tables, from the perspective of the materialized table, the update rate of the basic-tables is always very high. As a result, the refreshing probability of the materialized table is high, and the frequency of it being locked is also high. This makes the tenants almost unable to use the materialized table to improve the query efficiency, thus affecting the speed of business operations by the tenants. 
     BRIEF SUMMARY 
     In one embodiment of the present invention, a method for processing materialized tables in a multi-tenant application system, wherein in the multi-tenant application system, a plurality of tenants share one or more basic-tables, the method comprises, according to data access history information of the plurality of tenants, analyzing a similarity of update patterns for the one or more basic-tables by the plurality of tenants. Furthermore, the method comprises, according to the similarity of update patterns analyzed, grouping the plurality of tenants into a plurality of tenant groups. In addition, the method comprises, according to the plurality of tenant groups, constructing, by a processor, tenant group materialized tables from the one or more basic-tables. 
     Other forms of the embodiment of the method described above are in a computer program product and in a system. 
     The foregoing has outlined rather generally the features and technical advantages of one or more embodiments of the present invention in order that the detailed description of the present invention that follows may be better understood. Additional features and advantages of the present invention will be described hereinafter which may form the subject of the claims of the present invention. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       A better understanding of the present invention can be obtained when the following detailed description is considered in conjunction with the following drawings, in which: 
         FIG. 1  illustrates the relationships between basic-tables and a materialized table in accordance with an embodiment of the present invention; 
         FIG. 2  illustrates the architecture of a multi-tenant application system in which embodiments of the present invention can be realized; 
         FIG. 3A  illustrates a system for managing a materialized table in a multi-tenant application according to an embodiment of the present invention; 
         FIG. 3B  illustrates the relationship between the tenant group materialized tables constructed and the basic-tables in accordance with an embodiment of the present invention; 
         FIGS. 4A and 4B  illustrate the data and diagram reflecting the update patterns of the tenants in accordance with an embodiment of the present invention; 
         FIGS. 5A and 5B  illustrate the data and diagram obtained by further processing of the data of  FIG. 4A  in accordance with an embodiment of the present invention; 
         FIGS. 6A and 6B  illustrate the processing of the data and diagram of  FIGS. 4A and 4B  in accordance with an embodiment of the present invention; 
         FIG. 7  illustrates a part of the log contents as the source of the history information in accordance with an embodiment of the present invention; 
         FIG. 8  is a flowchart of a method for processing materialized tables in a multi-tenant application system in accordance with an embodiment of the present invention; and 
         FIG. 9  depicts an embodiment of a hardware configuration of a computer system which is representative of a hardware environment for practicing the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments of the present invention will now be described with reference to the accompanying drawings. In the following description, numerous details are described to enable the present invention to be fully understood. However, it is obvious to those skilled in the art that the realization of the present invention can be without some of these details. In addition, it should be appreciated that the present invention is not limited to the described specific embodiments. In contrast, it is contemplated to implement the present invention by using any combination of the following features and elements, no matter whether they involve different embodiments or not. Therefore, the following aspects, features, embodiments and advantages are illustrative, rather than elements or limitation of the appended claims, unless explicitly stated otherwise in the claims. 
     Referring to  FIG. 1 , it exemplarily illustrates the relationship between basic-tables and a materialized table in accordance with an embodiment of the present invention. 
     The left side of  FIG. 1  illustrates basic-tables BT  101 ,  102 ,  103 , while the right side illustrates a materialized table MV 0   104  corresponding to the basic-tables. 
       FIG. 1  exemplifies three basic-tables, i.e., “EMPLOYEE” (employee)  101 , “SALARY” (salary)  102  and “SALARYITEM” (salary item)  103 . 
     The attributes of the basic-table “EMPLOYEE”  101  include a primary key EMP_ID (employee identification), NAME (name), BAND (band) and AGE (age). 
     The attributes of the basic-table “SALARY”  102  include a primary key SAL_ID (salary identification), foreign key EMP_ID (employee identification) and MONTH (month). 
     The attributes of the basic-table “SALARYITEM”  103  include a primary key SI_ID (salary item identification), foreign key EMP_ID (employee identification), WORKITEM (work item), WORKTIME (work time) and INCOME (income). 
     The three basic-tables can be associated by primary and foreign keys. For example, the basic-table “EMPLOYEE”  101  is associated with the basic-table “SALARY”  102  by the primary key (PK) EMP_ID of the basic-table “EMPLOYEE”  101  and the foreign key (FK) EMP_ID of the basic-table “SALARY”  102 ; similarly, the basic-table “SALARY”  102  is associated with the basic-table “SALARYITEM”  103  by the primary key (PK) SAL_ID of the basic-table “SALARY”  102  and the foreign key (FK) SAL_ID of the basic-table “SALARYITEM”  103 . Thus, the three basic-tables “EMPLOYEE”  101 , “SALARY”  102  and “SALARYITEM”  103  can be associated, and a materialized table  104  can be constructed through such association. 
     The database schema definition language (DDL) is a language for describing real world entities to be stored in the database. A database system usually uses a DDL script to construct a materialized table. 
     The following is an example of a DDL script to create a materialized table MV 0   104  named EMPL_SALARY using the above three basic-tables of EMPLOYEE  101 , SALARY  102  and SALARYITEM  103 . 
     CREATE TABLE EMPL_SALARY AS (SELECT E.NAME, S.MONTH, AMOUNT(I.INCOME), AMOUNT(I.WORKTIME) FROM EMPLOYEE E, SALARY S, SALARYITEM I WHERE E.EMP_ID=S.EMP_ID AND S. SAL_ID=I.SAL_ID) 
     Data Initially Deferred Refresh Deferred 
     The constructed materialized table MV 0   104  is shown as the right side of  FIG. 1 . Materialized table  104  includes the following attributes (not shown): NAME, MONTH, AMOUNT (I.INCOME), AMOUNT (LWORKTIME), wherein AMOUNT (LINCOME) denotes the total income, AMOUNT (I.WORKTIME) denotes the total work time, and therefore, the contents of materialized table  104  contain someone (NAME)&#39;s total income and total work amount in a month (MONTH). 
       FIG. 2  schematically shows the architecture of a multi-tenant application system  200 , in which various embodiments of the present invention can be realized. The architecture shown in  FIG. 2  includes a server  21 , an access router  22 , a database  23  for storing multi-tenant application data, and a repository  24  for storing multi-tenant metadata, where the database  23  includes a basic-table BT and a corresponding materialized table MV shared by the plurality of tenants, T 1 , T 2 , . . . , Tn of the multi-tenant application  25 . 
     The DDL script for constructing the materialized table can also be stored in, e.g., a database  23 . 
     When a tenant Tn in the plurality of tenants T 1 , T 2  . . . Tn of multi-tenant application system  200  send a request relating to accessing database  23  through multi-tenant application  25 , access router  22  routes the tenant&#39;s request to server  21  to execute the requested service according to the metadata in repository  24 . 
     The request relating to accessing the database issued by the tenant can be a query to the contents of database  23 . For a complex SQL query, server  21  determines whether there is a materialized table available for the tenant&#39;s query request according to the identification of the tenant. If there is, server  21  performs the query on the materialized table MV; otherwise, server  21  performs the query on the basic-table BT. If the tenant&#39;s request is only a simple query requiring the basic data in the basic-table, server  21  only needs to perform the query on the basic-table BT shared by tenants. 
     The request relating to accessing the database issued by the tenant may also be to update the contents of database  23 . Server  21  can perform the update operation on the basic-table BT according to the request, e.g., performing operations of addition, deletion or modification on the data in the basic-table. 
     During the process that server  21  performs update operations on the basic-table, the corresponding materialized table MV is locked, and other tenants cannot access the locked materialized table. After the update operation on the basic-table is accomplished, the materialized table will be synchronized with the basic-table. For example, the original materialized table is deleted, and a new materialized table is created or constructed based on the updated basic-table. 
     The operations performed by server  21  are preserved as history information. The data access history of tenants is also a part of the history information. One example of the history information is system log  26 , e.g., the information recorded in log  26  on the tenants&#39; access to the data, including the operation times, tenants involved and operation types. 
       FIG. 3A  illustrates a system  300  for managing a materialized table in a multi-tenant application according to an embodiment of the present invention. 
     System  300  for managing the materialized table in the multi-tenant application shown in  FIG. 3A  includes the same or equivalent components as in the architecture shown in  FIG. 2 , e.g., a server  21 , an access router  22 , a database  23  which includes basic-tables BT shared by a plurality of tenants, T 1 , T 2  . . . Tn of the multi-tenant application system, a repository  24  for storing multi-tenant metadata, etc. Database  23  may further store a materialized table MV corresponding to the basic-tables BT shared by the plurality of tenants T 1 , T 2  . . . Tn. 
     Similarly, the operations performed by server  21  are preserved as history information, e.g., recorded in log  26 . For example, log  26  records the history information of data access by tenants, including the operation times, the tenants involved and the operation types. 
     As described above in conjunction with  FIG. 2 , the materialized table MV is shared by a plurality of tenants, and is associated with one or more basic-tables BT. 
     Compared with  FIG. 2 , system  300  of  FIG. 3A  further comprises an apparatus  301  for managing a materialized table in a multi-tenant application; the apparatus  301  comprises an update pattern analyzer  35 , a tenant grouping means  36  and a materialized table constructor  37 . In one embodiment, the components of apparatus  301  are software components which may reside in an application to be executed by a processor. 
     Therein update pattern analyzer  35  is for, according to the history information of data access of a plurality of tenants T 1 , T 2  . . . Tn, analyzing the similarity degree of the update patterns (referred to as “update pattern” or “tenant&#39;s update pattern” for short herein) for the basic-table BT by the plurality of tenants. 
     In the following will be described specific implementations of update pattern analyzer  35  analyzing the similarity degree of the update patterns in more detail in conjunction with  FIGS. 4A and 4B . 
     Referring again to  FIG. 3A , tenant grouping means  36  is for, according to the similarity degree analyzed by update pattern analyzer  35 , grouping the plurality of tenants T 1 , T 2  . . . Tn into a plurality of tenant groups. 
     For example, tenant grouping means  36  groups the plurality of tenants into two tenant groups, TG 1  and TG 2  (not shown in  FIG. 3A ), where the tenants included in the tenant group TG 1  have similar update patterns to each other; the tenants included in the tenant group TG 2  have similar update patterns to each other. Of course, tenant grouping means  36  may also group the plurality of tenants into more than two tenant groups according to specific conditions. 
     Materialized table constructor  37  is for constructing a tenant group materialized table according to the tenant groups grouped by tenant grouping means  36 . 
     For example, tenant grouping means  36  groups the plurality of tenants into two tenant groups, TG 1  and TG 2 . According to such grouping, materialized table constructor  37  constructs two tenant group materialized tables MV 1  and MV 2  from the basic-tables BT, as shown in  FIG. 3B  in accordance with an embodiment of the present invention. The two tenant group materialized tables MV 1  and MV 2  correspond to the tenant groups TG 1  and TG 2 , respectively. 
     The structures of the tenant group materialized tables MV 1  and MV 2  are the same as that of the materialized table MV, only the contents thereof differ according to the different tenant groups. For example, the tenant group materialized table MV 1  only contains data related to the tenants in the tenant group TG 1 . 
     In the following will be further described specific implementations of materialized table constructor  37  constructing tenant group MVs according to tenant grouping in conjunction with  FIGS. 6A and 6B . 
     Referring again to  FIG. 3A , according to an embodiment of the present invention, the apparatus for managing materialized tables in a multi-tenant application further comprises a materialized table scheduler  38 . 
     Materialized table scheduler  38  is for determining whether to enable or disable a corresponding tenant group materialized table based on the updates to the basic-table by the tenants. 
     According to an embodiment of the present invention, materialized table scheduler  38  determines, according to the determination that currently at least one tenant among the plurality of tenants will make large-scale updates to the basic-table, to disable the tenant group materialized table of the tenant group to which the tenant belongs. That is to say, if materialized table scheduler  38  determines that currently large-scale updates to the basic-table by the tenant will happen, it marks the state of the tenant group materialized table of the tenant group to which the tenant belongs from “enabled” to “disabled.” 
     According to another embodiment of the present invention, after the at least one tenant among the plurality of tenants performs the large-scale updates to the basic-table, materialized table scheduler  38  determines to enable the tenant group materialized table, constructed by materialized table constructor  37 , of the tenant group to which the tenant belongs. That is to say, after the tenant performs the large-scale updates to the basic-table, materialized table scheduler  38  constructs a tenant group materialized table of the tenant group to which the tenant belongs to replace the disabled tenant group materialized table, and marks the state of the newly constructed tenant group materialized table from “disabled” to “enabled.” 
     According to the present invention, access router  22  of multi-tenant application system  300  may, in response to a data access request, e.g., an SQL request, from a tenant, according to the corresponding relationship between the groups and the tenant group materialized tables stored in the multi-tenant metadata, route the SQL request to the tenant group materialized table of the tenant group to which the tenant belongs. 
     Now specific implementations of update pattern analyzer  35  analyzing the similarity degree of the update patterns will be described in more detail in conjunction with  FIGS. 4A and 4B . 
     It is discovered that for some tenant groups, their update patterns have certain similarities. 
     According to an embodiment of the present invention, the similarity degree of the update patterns analyzed by update pattern analyzer  35  includes adjacency in time of performing deletion, insertion or rewriting operations on records of the associated basic-tables of the materialized table. 
     In other words, in the embodiment, the update pattern, i.e., the mode of performing deletion, insertion or rewriting operations on records of the associated basic-tables of the materialized table, includes the timing for performing deletion, insertion or rewriting operations on records of the associated basic-tables of the materialized table. 
     Referring to  FIG. 4A , in conjunction with  FIG. 1 , it schematically illustrates in the form of a table the update patterns of different tenants to the basic-tables BT shown in  FIG. 1  in accordance with an embodiment of the present invention. 
     T 1 , T 2  . . . Tn in the first column of  FIG. 4A  denote different tenants, and 1, 2, . . . 15 in the first row denote different times (or time periods), here assuming that they denote the first day, the second day . . . , the 15 th  day of each month. Each unit, except those in the first row and the first column, denotes the number of times of updates by a tenant to the basic-tables BT (“EMPLOYEE”  101 , “SALARY”  102  or “SALARYITEM”  103 ) at some day. For example, as shown in the second column, on the second day, tenant T 5  performs  320  updates, and tenant T 10  performs  110  updates, and the rest of the tenants do not update on the second day. It can be seen from the table of  FIG. 4A  that, tenant T 7  and tenant T 9  perform large amount of updates on the 9 th  day, and tenants T 4  and T 8  perform large amount of updates on the 12 th  day. 
     The update patterns of tenants T 1 , T 2  . . . T 10  can also be denoted by the diagram of  FIG. 4B  in accordance with an embodiment of the present invention. The horizontal coordinate of  FIG. 4B  denotes time, and the vertical coordinate of  FIG. 4B  denotes the number of times of updates. The diagram of  FIG. 4B , from which the distribution of the tenant updates in terms of time can be observed intuitively, can be derived from the data in the table shown in  FIG. 4A . 
     As can be seen intuitively from  FIG. 4B , the curves to which tenant T 5  and tenant T 10  correspond overlap at time T 2 , which indicates that both tenant T 5  and tenant T 10  perform large amount of updates on the 2 nd  day. Therefore, in terms of update times, the update patterns of tenant T 5  and T 10  are similar, or with higher similarity. 
     Also, the update patterns of tenant T 7  and tenant T 9  have high similarity, the update patterns of tenant T 4  and tenant T 8  have high similarity, and the update patterns of tenant T 1  and tenant T 2  have high similarity. 
     According to an embodiment of the present invention, the data access history information based on which update pattern analyzer  35  analyzes the similarity degree of the update patterns is obtained from the information on the tenants&#39; data access operations recorded in log  26  ( FIGS. 2 and 3 ). 
     For example, the data shown in  FIG. 4A  can be collected from the history information of previous operations on the database (basic-tables, materialized table) by the tenants. 
     In the following will be described in more detail specific implementations of collecting the data from log  26  of the computer system in conjunction with  FIG. 7 . 
     As known by those skilled in the art, according to the data, various means can be used to analyze the similarity degree of the update patterns of the tenants. 
     As described above in conjunction with  FIG. 3A , tenant grouping means  36  of the present invention then, according to the similarity degree of the update patterns for the associated basic-tables of the materialized table by the plurality of tenants, groups the plurality of tenants into a plurality of tenant groups, as shown in  FIG. 6A , in accordance with an embodiment of the present invention. 
     Referring to  FIG. 6A , in conjunction with  FIG. 3A , for example, tenants T 1 -T 10  are grouped into six groups, TG 1 -TG 6 ; tenants T 1  and T 2  are grouped into tenant group TG 1 ; tenants T 5  and T 10  are grouped into tenant group TG 2 ; tenants T 4  and T 8  are grouped into tenant group TG 3 ; tenants T 7  and T 9  are grouped into tenant group TG 4 ; tenant group TG 5  only contains tenant T 3  and tenant group TG 6  only contains tenant TG 6 . The top table of  FIG. 6A  further illustrates that corresponding to tenant groups TG 1 -TG 6 , large-scale updates to the basic-tables happen on the 13 th , 2 nd , 12 th , 9 th , 5 th  and 6 th  days, respectively. 
     According to an embodiment of the present invention, tenant grouping means  36  may further store the information on the corresponding relationships between the tenants and the tenant groups and/or the times of large scale updates as shown in  FIG. 6A  in repository  24  as part of the metadata. The information can be used by materialized table constructor  37  or by access router  22 . 
     As described above in conjunction with  FIG. 3A , materialized table constructor  37  of the present invention may, then, according to the tenant groups grouped by tenant grouping means  36 , construct corresponding tenant group materialized tables. 
     According to an embodiment of the present invention, materialized table constructor  37  may, according to the tenant groups, construct tenant group materialized tables by using a DDL script. 
     For example, materialized table constructer  37  may obtain the pre-defined DDL script, e.g., the DDL script described above in conjunction with  FIG. 1 , and modify the DDL script by using the tenant grouping information from MV grouping means  36  or from the metadata, and then construct tenant group materialized tables for the tenant groups by using the modified DDL script. 
     For example, referring to  FIG. 6B , creating a tenant group materialized table EMPL_SALARY_TG 1  for the tenant group TG 1  including tenant T 1  and T 2  can be realized by the following modified DDL script: 
     CREATE TABLE EMPL_SALARY AS (SELECT E.NAME, S.MONTH, AMOUNT(I.INCOME), AMOUNT(I.WORKTIME) FROM EMPLOYEE E, SALARY S, SALARYITEM I WHERE E.EMP_ID=S.EMP_ID AND S. SAL_ID=I.SAL_ID) AND a.tenantID IN (‘T 1 ’, ‘T 2 ’) AND c.tenantID IN (‘T 1 ’, ‘T 2 ’) 
     Data Initially Deferred Refresh Deferred 
     The above modification to the DDL script is to add the code denoting the member tenants, tenant T 1  and tenant T 2 , of the tenant group TG 1 , “AND a. tenant ID IN (‘T 1 ’, ‘T 2 ’) AND c.tenantID IN (‘T 1 ’, ‘T 2 ’)”, so that the constructed tenant group materialized table EMPL_SALARY_TG 1  only includes the data associated with the members of the tenant group TG 1 , i.e., tenant T 1  and tenant T 2 . 
     For further example, the following is the code implementation of creating a tenant group materialized table EMPL_SALARY_TG 2  for the tenant group TG 2  including tenants T 5  and T 10 . 
     CREATE TABLE EMPL_SALARY AS (SELECT E.NAME, S.MONTH, AMOUNT(I.INCOME), AMOUNT(I.WORKTIME) FROM EMPLOYEE E, SALARY S, SALARYITEM I WHERE E.EMP_ID=S.EMP_ID AND S. SAL_ID=I.SAL_ID) AND a.tenantID IN (‘T 5 ’,‘T 10 ’) AND c.tenantID IN (‘T 5 ’,‘T 10 ’) 
     Data Initially Deferred Refresh Deferred 
     Therein, the code “AND a.tenantID IN (‘T 5 ’, ‘T 10 ’) AND c.tenant ID IN (&#39;T 5 ′, ‘T 10 ’)” denote that the constructed tenant group materialized table EMPL_SALARY_TG 2  only includes data associated with the members of the tenant group TG 2 , i.e., T 5  and T 10 . 
     Similarly, tenant group materialized tables EMPL_SALARY_TG 3 -EMPL_SALARY_TG 6  can be created for the other tenant groups TG 3 -TG 6 , thus creating 6 tenant group materialized tables, EMPL_SALARY_TG 1 -EMPL_SALARY_TG 6 . As shown in  FIG. 6B , the 6 tenant group materialized tables correspond to the 6 tenant groups TG 1  . . . TG 6 , respectively, in accordance with an embodiment of the present invention. As known by those skilled in the art, the constructed tenant group materialized tables EMPL_SALARY_TG 1  . . . EMPL_SALARY_TG 6  have the same structures as that of the materialized table EMPL_SALARY, but the contents are different, with a tenant group materialized table only involving the contents of the tenants in a corresponding tenant group. For example, EMPL_SALARY_TG 1  only contain contents related to tenants T 1  and T 2 . 
     Referring to  FIG. 6B , in conjunction with  FIG. 3A , according to an embodiment of the present invention, materialized table constructor  37  may record the information on the corresponding relationships between the tenant group materialized tables and the tenant groups shown in  FIG. 6B  into repository  24  as part of the metadata. The information can be used by materialized table scheduler  38  or by access router  22 . 
     The table shown in  FIG. 6B  further has a column of data denoted with the title of “state” for denoting the states of the corresponding tenant group MV. If the state is “enabled,” then this indicates that the corresponding tenant group MV has been synchronized with its basic-tables, and is usable. If the state is “disabled,” then this indicates that the corresponding tenant group MV is not usable. 
     According to an embodiment of the present invention, after constructor  37  newly constructs a tenant group materialized table, it sets the state of the newly constructed tenant group materialized table as “enabled,” and stores the state information in repository  24  as part of the metadata. The information can be used by materialized table scheduler  38  or by access router  22 . 
     As described in above in conjunction with  FIG. 3A , materialized table scheduler  38  is for, based on updates to basic-tables by tenants, determining whether to enable or disable corresponding tenant group materialized tables. Materialized table scheduler  38  may, when determining that large scale updates to a basic-table by a tenant will happen, mark the state of the tenant group materialized table of the tenant group to which the tenant belongs from “enabled” to “disabled”; after the tenant performs the large scale updates to the basic-tables, construct, by materialized table constructor  37 , a tenant group materialized table of the tenant group to which the tenant belongs to replace the disabled tenant group materialized table, and the state of the newly constructed tenant group materialized table is marked from “disabled” to “enabled.” The change of the state of the tenant group materialized table caused by materialized table scheduler  38  can also be recorded in repository  24  as part of the metadata. 
     An embodiment of the similarity of the update patterns of the tenants will be described and analyzed below in more detail. According to the embodiment, similarity of the update patterns of the tenant is analyzed by performing normalization on the data of the tenants updating basic-tables, e.g., as shown in  FIGS. 4A-4B . 
     The normalization can be performed according to the following formula, so that after the normalization, the maximum value of the update times of each tenant at a specific time is 1, and the minimum value is 0. 
     
       
         
           
             
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     In the above formula, X ij  denotes that a tenant updates j times on the i th  day; min{x ij } denotes the minimum number of times of daily updates by a tenant within i days excluding the i th  day; max{x ij } denotes the maximum number of times of updates of a tenant within the i days, including the i th  day. 
     Referring to  FIG. 4A , for tenant T 1 , it updates 100 times on the 13 th  day, with a maximum number of times of updates of 100, and at other times, its minimum number of times of daily updates is 0. 
     So, put the above values into the formula: 
     When i=13, x ij =100, max{x ij }=100, min {x ij }=0, 
     so Σx y=(100−0)/(100−0)=1;    
     when i=other values, x ij =0, max{x ij }=100, min {x ij }=0, 
     so Σx ij=(0−0)/(100−0)=0.    
     After the normalization, the maximum value of the refresh times of tenant T 1  is 1, and the minimum value is 0. 
     For the tenant T 2 , it updates 220 times on the 13 th  day, with a maximum number of times of updates of 220, and the minimum number of times of daily updates is 0 at other times. 
     So, put the above values into the formula: 
     When i=13, x ij =220, max{x ij} =220, min{x ij }=0, 
     So Σx ij=(220−0)/(220−0)=1;    
     When i=other values, x ij =0, max{x ij }=220, min{x ij }=0, 
     So Σx ij=(0−0)/(220−0)=0.    
     Performing the same processing on the data of all the tenants in  FIG. 4A  can obtain the data table shown in  FIG. 5A  in accordance with an embodiment of the present invention. After the normalization process, the data table shown in  FIG. 5A  includes two values of 0 and 1, where value 1 denotes that large scale updates happens, and value 0 indicates that no updates happens, or the number of times of the updates is smaller than a predetermined threshold, and thus can be omitted. 
     From the data table, the graph shown in  FIG. 5B  can be derived, where the horizontal coordinate denotes time, and the vertical coordinate denotes the number of times of updates that has been normalized in accordance with an embodiment of the present invention. 
     From  FIG. 4B , the distribution of the tenants&#39; updates in time can be visually observed. For example, referring to  FIG. 5B , the curve denoting the update pattern of tenant T 1  is TG 1 , and the curve denoting the update pattern of tenant T 2  is also TG 1 . 
     In other words, after the normalization, the curve denoting the update pattern of tenant T 1  overlaps the curve denoting the update pattern of tenant T 2 , which indicates that the update patterns of the two tenants are highly similar. Therefore, tenants T 1  and T 2  are put in the same tenant group TG 1 . 
     Now specific implementations are described for collecting these data from the log of the computer system in conjunction with  FIG. 7 . 
     As described above, when the present invention is implemented, information about the tenants&#39; data access operations can be obtained from log  26  of the computer system for analyzing the similarity of the update patterns of the tenants. 
     It is a common technique for those skilled in the art to use the information in log  26  as the history information to analyze the operations of the computer user. 
     According to an embodiment of the present invention, update pattern analyzer  35  ( FIG. 3A ) first collects information about the tenant&#39;s data access operations from log  26  ( FIG. 3A ), to obtain part of the log contents as shown in  FIG. 7  in accordance with an embodiment of the present invention. Referring to  FIG. 7 , in conjunction with  FIGS. 1 and 3A , the log data shown in  FIG. 7  records details of the tenants performing update operations on the database, including the time  71  when the operation happens (e.g., “2009-11-13 16:23:51, 640”), tenant  72  (e.g., “{conn-100001-T1}”), and operation  73  (e.g., “insert salary values”), where the type of the operation “insert salary values” is data insertion, which is an operation to perform updates to the basic-table (e.g., the basic-table of “SALARY”  102  shown in  FIG. 1 ). 
     According to an embodiment of the present invention, a data table as shown in  FIG. 4A  can be constructed according to the above collected log data, for analyzing the similarity of the tenants&#39; update patterns. 
     Various implementations of apparatus  301  ( FIG. 3A ) for managing a materialized table in a multi-tenant application of the present invention have been described through the above embodiments. Under the same inventive concept, the present invention also provides a method for processing materialized tables in a multi-tenant application system. 
       FIG. 8  is a flowchart of a method  800  for processing materialized tables in a multi-tenant application system as shown in  FIG. 3A  in accordance with an embodiment of the present invention. 
     Referring to  FIG. 8 , in conjunction with  FIG. 3A , in step  801 , according to the plurality of tenants&#39; data access history information, the similarity of the update patterns for the one or more basic-tables by the plurality of tenants is analyzed. 
     In step  802 , according to the similarity analyzed by update pattern analyzer  35 , the plurality of tenants are grouped into a plurality of tenant groups. 
     In step  803 , according to the tenant groups grouped by tenant grouping means  36 , the tenant group materialized tables are constructed from the one or more basic-tables. 
     In some implementations, method  800  may include other and/or additional steps that, for clarity, are not depicted. Further, in some implementations, method  800  may be executed in a different order presented and that the order presented in the discussion of  FIG. 8  is illustrative. Additionally, in some implementations, certain steps in method  800  may be executed in a substantially simultaneous manner or may be omitted. 
     According to an embodiment of the present invention, the method is further for, based on updates to the one or more basic-tables by a tenant, determining whether to enable or disable the corresponding tenant group materialized table. 
     According to an embodiment of the present invention, the method is further for, based on the determination that currently at least one tenant in the plurality of tenants will perform large scale updates to a basic-table, disabling the tenant group materialized table of the tenant group to which the tenant belongs. 
     According to an embodiment of the present invention, the method is further for, after the at least one tenant in the plurality of tenants perform large scale updates to a basic-table, enabling the tenant group materialized table, constructed by materialized table constructor  37 , of the tenant group to which the tenant belongs. 
     In the various embodiments of the above method, the similarity degree of the update patterns includes adjacency in time of performing deletion, insertion or rewriting operations on records of the associated basic-tables of the materialized table. 
     According to an embodiment of the present invention, in the various embodiments of the above method, a DDL script can be used to construct a tenant group materialized table corresponding to a tenant group. 
     According to an embodiment of the present invention, in the various embodiments of the above method, at least one of the following is stored: the corresponding relationships between tenants and tenant groups; the large-scale update times of tenants; the information about tenant group materialized tables being enabled or disabled. For example, they are stored as part of the multi-tenant metadata of the multi-tenant application system. 
     According to an embodiment of the present invention, in the various embodiments of the above method, the data access history information is the information of the data access operations of the tenants recorded in log  26  of the multi-tenant application system. 
     Apparatus  301  and its various embodiments described above can be used to illustrate and realize various embodiments of method  800  for processing materialized tables in a multi-tenant application system of the present invention. For simplicity, in the above description of the various embodiments of method  800 , part of the contents repeating the above description of the corresponding apparatus  301  are omitted. Therefore, details of the apparatus can be learned by referring to the above description of the corresponding method. 
     The above description and illustration of apparatus  301  and method  800  for processing materialized tables in a multi-tenant application system and their embodiments are only exemplary, rather than limitation to the present invention. In other embodiments of the present invention, the apparatus may have more, less or different modules, and the connection or inclusion relationships between the modules can be different from that is described or illustrated. 
       FIG. 9  depicts an embodiment of a hardware configuration of a computer system  900  which is representative of a hardware environment for practicing the present invention. Referring to  FIG. 9 , computer system  900  has a processor  901  coupled to various other components by system bus  902 . An operating system  903  may run on processor  901  and provide control and coordinate the functions of the various components of  FIG. 9 . An application  904  in accordance with the principles of the present invention may run in conjunction with operating system  903  and provide calls to operating system  903  where the calls implement the various functions or services to be performed by application  904 . Application  904  may include, for example, an application for processing materialized tables in a multi-tenant application system as discussed above. 
     Referring again to  FIG. 9 , read-only memory (“ROM”)  905  may be coupled to system bus  902  and include a basic input/output system (“BIOS”) that controls certain basic functions of computer device  900 . Random access memory (“RAM”)  906  and disk adapter  907  may also be coupled to system bus  902 . It should be noted that software components including operating system  903  and application  904  may be loaded into RAM  906 , which may be computer system&#39;s  900  main memory for execution. Disk adapter  907  may be an integrated drive electronics (“IDE”) adapter that communicates with a disk unit  908 , e.g., disk drive. 
     Computer system  900  may further include a communications adapter  909  coupled to bus  902 . Communications adapter  909  may interconnect bus  902  with an outside network (not shown) thereby allowing computer system  900  to communicate with other similar devices. 
     I/O devices may also be connected to computer system  900  via a user interface adapter  910  and a display adapter  911 . Keyboard  912 , mouse  913  and speaker  914  may all be interconnected to bus  902  through user interface adapter  910 . Data may be inputted to computer system  900  through any of these devices. A display monitor  915  may be connected to system bus  902  by display adapter  911 . In this manner, a user is capable of inputting to computer system  900  through keyboard  912  or mouse  913  and receiving output from computer system  900  via display  915  or speaker  914 . 
     As will be appreciated by one skilled in the art, aspects of the present invention may be embodied as a system, method or computer program product. Accordingly, aspects of the present invention may take the form of an entirely hardware embodiment, an entirely software embodiment (including firmware, resident software, micro-code, etc.) or an embodiment combining software and hardware aspects that may all generally be referred to herein as a “circuit,” ‘module” or “system.” Furthermore, aspects of the present invention may take the form of a computer program product embodied in one or more computer readable medium(s) having computer readable program code embodied thereon. 
     Any combination of one or more computer readable medium(s) may be utilized. The computer readable medium may be a computer readable signal medium or a computer readable storage medium. A computer readable storage medium includes an electronic, magnetic, optical, electromagnetic, or semiconductor system, apparatus, or device, or any suitable combination of the foregoing. More specific examples (a non-exhaustive list) of the computer readable storage medium would include the following: an electrical connection having one or more wires, a portable computer diskette, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or flash memory), a portable compact disc read-only memory (CD-ROM), an optical storage device, a magnetic storage device, or any suitable combination of the foregoing. In the context of this document, a computer readable storage medium may be any tangible medium that can contain, or store a program for use by or in connection with an instruction execution system, apparatus, or device. 
     A computer readable signal medium may include a propagated data signal with computer readable program code embodied therein, for example, in baseband or as part of a carrier wave. Such a propagated signal may take any of a variety of forms, including, but not limited to, electro-magnetic, optical, or any suitable combination thereof. A computer readable signal medium may be any computer readable medium that is not a computer readable storage medium and that can communicate, propagate, or transport a program for use by or in connection with an instruction execution system, apparatus or device. 
     Program code embodied on a computer readable medium may be transmitted using any appropriate medium, including but not limited to wireless, wireline, optical fiber cable, RF, etc., or any suitable combination of the foregoing. 
     Computer program code for carrying out operations for aspects of the present invention may be written in any combination of one or more programming languages, including an object oriented programming language such as Java, Smalltalk, C++ or the like and conventional procedural programming languages, such as the C programming language or similar programming languages. The program code may execute entirely on the user&#39;s computer, partly on the user&#39;s computer, as a stand-alone software package, partly on the user&#39;s computer and partly on a remote computer or entirely on the remote computer or server. In the latter scenario, the remote computer may be connected to the user&#39;s computer through any type of network; including a local area network (LAN) or a wide area network (WAN), or the connection may be made to an external computer (for example, through the Internet using an Internet Service Provider). 
     Aspects of the present invention are described above with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems) and computer program products according to embodiments of the present invention. It will be understood that each block of the flowchart illustrations and/or block diagrams, and combinations of blocks in the flowchart illustrations and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, or other programmable data processing apparatus to product a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the function/acts specified in the flowchart and/or block diagram block or blocks. 
     These computer program instructions may also be stored in a computer readable medium that can direct a computer, other programmable data processing apparatus, or other devices to function in a particular manner, such that the instructions stored in the computer readable medium produce an article of manufacture including instructions which implement the function/act specified in the flowchart and/or block diagram block or blocks. 
     The computer program instructions may also be loaded onto a computer, other programmable data processing apparatus, or other devices to cause a series of operational steps to be performed on the computer, other programmable apparatus or other devices to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide processes for implementing the function/acts specified in the flowchart and/or block diagram block or blocks. 
     Although the present invention has been illustrated and described with reference to preferred embodiments, those skilled in the art will understand that various changes both in form and details may be made thereto without departing from the spirit and scope of the present invention.