Abstract:
Techniques and mechanisms for analyzing a plurality of database queries within a database environment. A first statistical evaluation of a first query plan is determined for a first database query with at least one computing device within the database environment. A second statistical evaluation for a second query plan is determined for a second database query. The first statistical evaluation and the second statistical evaluation are compared to determine whether the first query plan matches the second query plan with at least one computing device within the database environment. An indication is stored in a repository of the database environment that the first query matches the second query if the first hash value matches the second hash value. A function that provides the first query plan is determined. If the second query plan is provided by the function that provides the first query plan, data objects referenced by the first query plan and the second query plan if the function provides both the first query plan and the second query plan to determine if the first query plan and the second query plan are syntactically different versions of equivalent database queries. Query statistics are stored in the statistical repository if the first query plan and the second query plan are syntactically different versions of equivalent database queries.

Description:
CLAIM OF PRIORITY 
       [0001]    This patent application is related to, and claims priority to, U.S. Provisional Patent Application No. 61/888,966 entitled “Analyzing an Automatic Workload Repository,” filed Oct. 9, 2013, the entire contents of which are incorporated herein by reference. 
     
    
     TECHNICAL FIELD 
       [0002]    Embodiments relate to techniques for analytics within a database environment. More particularly, embodiments relate to techniques and mechanisms for analyzing database query activities and managing associated data. 
       BACKGROUND 
       [0003]    To effectively manage a database environment, various statistics are gathered. Many database platforms generate different types of statistics for systems, sessions, individual Structured Query Language (SQL) statements, etc. These statistics can be used for system management, reporting, diagnostics, etc. One technique for analyzing performance is to determine changes in statistics over time. This requires gather of historical data. However, gathering of these statistics from multiple databases, or even from a single database, can be difficult because different databases or different SQL statements may be slightly different even if having the same functional result. Thus, it can be difficult to get a true picture of these statistics. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0004]    Embodiments of the invention are illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings in which like reference numerals refer to similar elements. 
           [0005]      FIG. 1  is a conceptual illustration of one embodiment of a technique and components of a tool to provide analysis for database queries. 
           [0006]      FIG. 2  is an example of the type of information that can be included in a result file used for managing and analyzing database queries. 
           [0007]      FIG. 3  is a block diagram of one environment wherein an on-demand database service might be used. 
           [0008]      FIG. 4  is a block diagram of one embodiment of elements of environment of  FIG. 3  and various possible interconnections between these elements. 
       
    
    
     DETAILED DESCRIPTION 
       [0009]    In the following description, numerous specific details are set forth. However, embodiments of the invention may be practiced without these specific details. In other instances, well-known circuits, structures and techniques have not been shown in detail in order not to obscure the understanding of this description. 
         [0010]    Databases have provided many performance gathering and reporting tools over the years. One such tool is an Automatic Workload Repository (AWR) available in ORACLE® databases. An AWR is used by a database system to collect various database statistics. such as wait events used to identify performance problems, time model statistics indicating the amount of DB time associated with a process, a active session history (ASH) statistics, object usage statistics, etc. Normally AWR information is unique to a specific database and database environment. Comparing AWR data from different databases is hard because each database, query, report, etc. has a different SQL ID, query format, different schema, etc. These shortcomings apply to other query statistical information as well. 
         [0011]    In one implementation, an intelligent tool bridges the problems described above. In one implementation, the intelligent tool can access and compare AWRs (or other statistical information) from different databases. This is not inherently easy to do, because different databases may have different object types and schemas. To compare AWRs, for example, in one implementation, the tool evaluates input files, maps SQL IDs to SQL text, maps SQL IDs to difference parameters and uses the SQL text and parameters as comparison input since SQL IDs may not be the same over two distinct databases. 
         [0012]    In one embodiment, by analyzing the extra data (e.g., SQL text and other parameters) the tool can determine which queries are like queries in the different database. Once it has done this analysis, in one implementation, the tool creates output files. These output files can be stored in a database, a statistics repository, etc. In one embodiment, the techniques described herein can be applied to all database queries and search plans. 
         [0013]      FIG. 1  is a conceptual illustration of one embodiment of a technique and components of a tool to provide analysis for database queries. Using the techniques and components described herein, if a particular query changes across a release, for example, the tool will be able to detect this change and provide an accurate analysis. Unlike, for example, simpler diff packages that are unable to relate SQLID changes to SQLTEXT. 
         [0014]    Also, the intelligent tool can help avoid needless lookups to the SQLTEXT anchor provided in the statistical reports because it resolves that on its own automatically. In other words, the tool can do head-to-head query comparisons regardless of the difference in software versions. In one implementation, the tool can relate queries to other queries and provide a “diff” of how the query has changes with software updates, query updates, etc. In one implementation, the intelligent tool can be used to compare data in a database when one or more databases are refreshed and the existing snapshots lost. 
         [0015]    In one embodiment, two or more input files are received,  110 . These files can be, for example, AWR files; however, other file formats (e.g., DB2) can also be supported. The AWR files provide individual SQL statements and cumulative and delta values for various query statistics at all levels except the session level. The delta values represent changes for each statistic over a time period. Some or all of this information can be used by the tool. 
         [0016]    Search identifiers and/or sources are mapped to search text,  120 . In one embodiment, SQL identifiers (II)s) are mapped to SQL text. In one embodiment, V$SQL can be utilized in the mapping. V$SQL lists statistics on shared SQL area without the GROUP BY clause and contains one row for each child of the original SQL text entered. Statistics displayed in V$SQL are normally updated at the end A query execution. However, for long running queries, they are updated every 5 seconds. This makes it easy to see the impact of long running SQL statements while they are still in progress. V$SQL further includes SQL text and SQL statements for the corresponding queries. 
         [0017]    The search identifiers are mapped to difference parameters,  130 . The various parameters to be compared are mapped, for example, redo size, logical reads, block changes, physical reads, physical writes, user calls, parses, hard parses, sorts, logons, executes, transactions. In one embodiment, the functions and/or procedure calls from which the queries originate may be utilized to for comparison/analysis purposes. Different and/or additional parameters can also be compared. By utilizing the mapping/conversions described herein, queries for different databases and/or different database versions can be analyzed, which was not possible using traditional techniques. 
         [0018]    The comparison(s) can then be performed utilizing the parameters and SQL text identified and mapped above,  140 . In one embodiment, a difference is determined between queries for the relevant parameters and a percentage difference can be provided. Using the percentage difference, queries can be considered matches even when there is no exact match (e.g., slight syntactical differences). 
         [0019]    The differences are stored in a difference file,  150 . One example of the type of information that can be stored in the difference file is provided in  FIG. 2 , which provides profile difference information  210  and/or SQL text difference information  220 . Additional and/or different parameters and/or SQL ext strings can also be included with statistical and analytical information. 
         [0020]      FIG. 3  illustrates a block diagram of an environment  310  wherein an on-demand database service might be used. Environment  310  may include user systems  312 , network  314 , system  316 , processor system  317 , application platform  318 , network interface  320 , tenant data storage  322 , system data storage  324 , program code  326 , and process space  328 . In other embodiments, environment  310  may not have all of the components listed and/or may have other elements instead of, or in addition to, those listed above. 
         [0021]    Environment  310  is an environment in which an on-demand database service exists. User system  312  may be any machine or system that is used by a user to access a database user system. For example, any of user systems  312  can be a handheld computing device, a mobile phone, a laptop computer, a work station, and/or a network of computing devices. As illustrated in herein  FIG. 3  (and in more detail in  FIG. 4 ) user systems  312  might interact via a network  314  with an on-demand database service, which is system  316 . 
         [0022]    An on-demand database service, such as system  316 , is a database system that is made available to outside users that do not need to necessarily be concerned with building and/or maintaining the database system, but instead may be available for their use when the users need the database system (e.g., on the demand of the users). Some on-demand database services may store information from one or more tenants stored into tables of a common database image to form a multi-tenant database system (MTS). Accordingly, “on-demand database service  316 ” and “system  316 ” will be used interchangeably herein. A database image may include one or more database objects. A relational database management system (RDMS) or the equivalent may execute storage and retrieval of information against the database object(s). Application platform  318  may be a framework that allows the applications of system  316  to run, such as the hardware and/or software, e.g., the operating system. In an embodiment, on-demand database service  316  may include an application platform  318  that enables creation, managing and executing one or more applications developed by the provider of the on-demand database service, users accessing the on-demand database service via user systems  312 , or third party application developers accessing the on-demand database service via user systems  312 . 
         [0023]    The users of user systems  312  may differ in their respective capacities, and the capacity of a particular user system  312  might be entirely determined by permissions (permission levels) for the current user. For example, where a salesperson is using a particular user system  312  to interact with system  316 , that user system has the capacities allotted to that salesperson. However, while an administrator is using that user system to interact with system  316 , that user system has the capacities allotted to that administrator. In systems with a hierarchical role model, users at one permission level may have access to applications, data, and database information accessible by a lower permission level user, but may not have access to certain applications, database information, and data accessible by a user at a higher permission level. Thus, different users will have different capabilities with regard to accessing and modifying application and database information, depending on a user&#39;s security or permission level. 
         [0024]    Network  314  is any network or combination of networks of devices that communicate with one another. For example, network  314  can be any one or any combination of a LAN (local area network), WAN (wide area network), telephone network, wireless network, point-to-point network, star network, token ring network, hub network, or other appropriate configuration. As the most common type of computer network in current use is a TCP/IP (Transfer Control Protocol and Internet Protocol) network, such as the global internetwork of networks often referred to as the “Internet” with a capital “I,” that network will be used in many of the examples herein. However, it should be understood that the networks that one or more implementations might use are not so limited, although TCP/IP is a frequently implemented protocol. 
         [0025]    User systems  312  might communicate with system  316  using TCP/IP and, at a higher network level, use other common Internet protocols to communicate, such as HTTP, FTP, AFS, WAP, etc. In an example where HTTP is used, user system  312  might include an HTTP client commonly referred to as a “browser” for sending and receiving HTTP messages to and from an HTTP server at system  316 . Such an HTTP server might be implemented as the sole network interface between system  316  and network  314 , but other techniques might be used as well or instead. In some implementations, the interface between system  316  and network  314  includes load sharing functionality, such as round-robin HTTP request distributors to balance loads and distribute incoming HTTP requests evenly over a plurality of servers. At least as for the users that are accessing that server, each of the plurality of servers has access to the MTS&#39; data; however, other alternative configurations may be used instead. 
         [0026]    In one embodiment, system  316 , shown in  FIG. 3 , implements a web-based customer relationship management (CRM) system. For example, in one embodiment, system  316  includes application servers configured to implement and execute CRM software applications as well as provide related data, code, forms, webpages and other information to and from user systems  312  and to store to, and retrieve from, a database system related data, objects, and Webpage content. With a multi-tenant system, data for multiple tenants may be stored in the same physical database object, however, tenant data typically is arranged so that data of one tenant is kept logically separate from that of other tenants so that one tenant does not have access to another tenant&#39;s data, unless such data is expressly shared. In certain embodiments, system  316  implements applications other than, or in addition to, a CRM application. For example, system  316  may provide tenant access to multiple hosted (standard and custom) applications, including a CRM application. User (or third party developer) applications, which may or may not include CRM, may be supported by the application platform  318 , which manages creation, storage of the applications into one or more database objects and executing of the applications in a virtual machine in the process space of the system  316 . 
         [0027]    One arrangement for elements of system  316  is shown in  FIG. 3 , including a network interface  320 , application platform  318 , tenant data storage  322  for tenant data  323 , system data storage  324  for system data  325  accessible to system  316  and possibly multiple tenants, program code  326  for implementing various functions of system  316 , and a process space  328  for executing MTS system processes and tenant-specific processes, such as running applications as part of an application hosting service. Additional processes that may execute on system  316  include database indexing processes. 
         [0028]    Several elements in the system shown in  FIG. 3  include conventional, well-known elements that are explained only briefly here. For example, each user system  312  could include a desktop personal computer, workstation, laptop, PDA, cell phone, or any wireless access protocol (WAP) enabled device or any other computing device capable of interfacing directly or indirectly to the Internet or other network connection. User system  312  typically runs an HTTP client, e.g., a browsing program, such as Microsoft&#39;s Internet Explorer browser, Netscape&#39;s Navigator browser, Opera&#39;s browser, or a WAP-enabled browser in the case of a cell phone, PDA or other wireless device, or the like, allowing a user (e.g., subscriber of the multi-tenant database system) of user system  312  to access, process and view information, pages and applications available to it from system  316  over network  314 . Each user system  312  also typically includes one or more user interface devices, such as a keyboard, a mouse, trackball, touch pad, touch screen, pen or the like, for interacting with a graphical user interface (GUI) provided by the browser on a display (e.g., a monitor screen, LCD display, etc.) in conjunction with pages, forms, applications and other information provided by system  316  or other systems or servers. For example, the user interface device can be used to access data and applications hosted by system  316 , and to perform searches on stored data, and otherwise allow a user to interact with various GUI pages that may be presented to a user. As discussed above, embodiments are suitable for use with the Internet, which refers to a specific global internetwork of networks. However, it should be understood that other networks can be used instead of the Internet, such as an intranet, an extranet, a virtual private network (VPN), a non-TCP/IP based network, any LAN or WAN or the like. 
         [0029]    According to one embodiment, each user system  312  and all of its components are operator configurable using applications, such as a browser, including computer code run using a central processing unit such as an Intel Pentium® processor or the like. Similarly, system  316  (and additional instances of an MTS, where more than one is present) and all of their components might be operator configurable using application(s) including computer code to run using a central processing unit such as processor system  317 , which may include an Intel Pentium® processor or the like, and/or multiple processor units. A computer program product embodiment includes a machine-readable storage medium (media) having instructions stored thereon/in which can be used to program a computer to perform any of the processes of the embodiments described herein. Computer code for operating and configuring system  316  to intercommunicate and to process webpages, applications and other data and media content as described herein are preferably downloaded and stored on a hard disk, but the entire program code, or portions thereof, may also be stored in any other volatile or non-volatile memory medium or device as is well known, such as a ROM or RAM, or provided on any media capable of storing program code, such as any type of rotating media including floppy disks, optical discs, digital versatile disk (DVD), compact disk (CD), microdrive, and magneto-optical disks, and magnetic or optical cards, nanosystems (including molecular memory ICs), or any type of media or device suitable for storing instructions and/or data. Additionally, the entire program code, or portions thereof, may be transmitted and downloaded from a software source over a transmission medium, e.g., over the Internet, or from another server, as is well known, or transmitted over any other conventional network connection as is well known (e.g., extranet, VPN, LAN, etc.) using any communication medium and protocols (e.g., TCP/IP, HTTP, HTTPS, Ethernet, etc.) as are well known. It will also be appreciated that computer code for implementing embodiments can be implemented in any programming language that can be executed on a client system and/or server or server system such as, for example, C, C++, HTML, any other markup language, Java™, JavaScript, ActiveX, any other scripting language, such as VBScript, and many other programming languages as are well known may be used. (Java™ is a trademark of Sun Microsystems, Inc.). 
         [0030]    According to one embodiment, each system  316  is configured to provide webpages, forms, applications, data and media content to user (client) systems  312  to support the access by user systems  312  as tenants of system  316 . As such, system  316  provides security mechanisms to keep each tenant&#39;s data separate unless the data is shared. If more than one MTS is used, they may be located in close proximity to one another (e.g., in a server farm located in a single building or campus), or they may be distributed at locations remote from one another (e.g., one or more servers located in city A and one or more servers located in city B). As used herein, each MTS could include one or more logically and/or physically connected servers distributed locally or across one or more geographic locations. Additionally, the term “server” is meant to include a computer system, including processing hardware and process space(s), and an associated storage system and database application (e.g., OODBMS or RDBMS) as is well known in the art. It should also be understood that “server system” and “server” are often used interchangeably herein. Similarly, the database object described herein can be implemented as single databases, a distributed database, a collection of distributed databases, a database with redundant online or offline backups or other redundancies, etc., and might include a distributed database or storage network and associated processing intelligence. 
         [0031]      FIG. 4  also illustrates environment  310 . However, in  FIG. 4  elements of system  316  and various interconnections in an embodiment are further illustrated.  FIG. 4  shows that user system  312  may include processor system  312 A, memory system  312 B, input system  312 C, and output system  312 D.  FIG. 4  shows network  314  and system  316 .  FIG. 4  also shows that system  316  may include tenant data storage  322 , tenant data  323 , system data storage  324 , system data  325 , User Interface (UI)  430 , Application Program Interface (API)  432 , PL/SOQL  434 , save routines  436 , application setup mechanism  438 , applications servers  400   1 - 400   N , system process space  402 , tenant process spaces  404 , tenant management process space  410 , tenant storage area  412 , tenant data  414 , and application metadata  416 . In other embodiments, environment  310  may not have the same elements as those listed above and/or may have other elements instead of, or in addition to, those listed above. 
         [0032]    User system  312 , network  314 , system  316 , tenant data storage  322 , and system data storage  324  were discussed above in  FIG. 3 . Regarding user system  312 , processor system  312 A may be any combination of one or more processors. Memory system  312 B may be any combination of one or more memory devices, short term, and/or long term memory. Input system  312 C may be any combination of input devices, such as one or more keyboards, mice, trackballs, scanners, cameras, and/or interfaces to networks. Output system  312 D may be any combination of output devices, such as one or more monitors, printers, and/or interfaces to networks. As shown by  FIG. 4 , system  316  may include a network interface  320  (of  FIG. 3 ) implemented as a set of HTTP application servers  400 , an application platform  318 , tenant data storage  322 , and system data storage  324 . Also shown is system process space  402 , including individual tenant process spaces  404  and a tenant management process space  410 . Each application server  400  may be configured to tenant data storage  322  and the tenant data  323  therein, and system data storage  324  and the system data  325  therein to serve requests of user systems  312 . The tenant data  323  might be divided into individual tenant storage areas  412 , which can be either a physical arrangement and/or a logical arrangement of data. Within each tenant storage area  412 , tenant data  414  and application metadata  416  might be similarly allocated for each user. For example, a copy of a user&#39;s most recently used (MRU) items might be stored to tenant data  414 . Similarly, a copy of MRU items for an entire organization that is a tenant might be stored to tenant storage area  412 . A UI  430  provides a user interface and an API  432  provides an application programmer interface to system  316  resident processes to users and/or developers at user systems  312 . The tenant data and the system data may be stored in various databases, such as one or more Oracle™ databases. 
         [0033]    Application platform  318  includes an application setup mechanism  438  that supports application developers&#39; creation and management of applications, which may be saved as metadata into tenant data storage  322  by save routines  436  for execution by subscribers as one or more tenant process spaces  404  managed by tenant management process space  410  for example. Invocations to such applications may be coded using PL/SOQL  434  that provides a programming language style interface extension to API  432 . A detailed description of some PL/SOQL language embodiments is discussed in commonly owned U.S. Pat. No. 7,730,478 entitled, “Method and System for Allowing Access to Developed Applicants via a Multi-Tenant Database On-Demand Database Service”, issued Jun. 1, 2010 to Craig Weissman, which is incorporated in its entirety herein for all purposes. Invocations to applications may be detected by one or more system processes, which manage retrieving application metadata  416  for the subscriber making the invocation and executing the metadata as an application in a virtual machine. 
         [0034]    Each application server  400  may be communicably coupled to database systems, e.g., having access to system data  325  and tenant data  323 , via a different network connection. For example, one application server  400   1  might be coupled via the network  314  (e.g., the Internet), another application server  400   N - 1  might be coupled via a direct network link, and another application server  400   N  might be coupled by yet a different network connection. Transfer Control Protocol and Internet Protocol (TCP/IP) are typical protocols for communicating between application servers  400  and the database system. However, it will be apparent to one skilled in the art that other transport protocols may be used to optimize the system depending on the network interconnect used. 
         [0035]    In certain embodiments, each application server  400  is configured to handle requests for any user associated with any organization that is a tenant. Because it is desirable to be able to add and remove application servers from the server pool at any time for any reason, there is preferably no server affinity for a user and/or organization to a specific application server  400 . In one embodiment, therefore, an interface system implementing a load balancing function (e.g., an F5 Big-IP load balancer) is communicably coupled between the application servers  400  and the user systems  312  to distribute requests to the application servers  400 . In one embodiment, the load balancer uses a least connections algorithm to route user requests to the application servers  400 . Other examples of load balancing algorithms, such as round robin and observed response time, also can be used. For example, in certain embodiments, three consecutive requests from the same user could hit three different application servers  400 , and three requests from different users could hit the same application server  400 . In this manner, system  316  is multi-tenant, wherein system  316  handles storage of, and access to, different objects, data and applications across disparate users and organizations. 
         [0036]    As an example of storage, one tenant might be a company that employs a sales force where each salesperson uses system  316  to manage their sales process. Thus, a user might maintain contact data, leads data, customer follow-up data, performance data, goals and progress data, etc., all applicable to that user&#39;s personal sales process (e.g., in tenant data storage  322 ). In an example of a MTS arrangement, since all of the data and the applications to access, view, modify, report, transmit, calculate, etc., can be maintained and accessed by a user system having nothing more than network access, the user can manage his or her sales efforts and cycles from any of many different user systems. For example, if a salesperson is visiting a customer and the customer has Internet access in their lobby, the salesperson can obtain critical updates as to that customer while waiting for the customer to arrive in the lobby. 
         [0037]    While each user&#39;s data might be separate from other users&#39; data regardless of the employers of each user, some data might be organization-wide data shared or accessible by a plurality of users or all of the users for a given organization that is a tenant. Thus, there might be some data structures managed by system  316  that are allocated at the tenant level while other data structures might be managed at the user level. Because an MTS might support multiple tenants including possible competitors, the MTS should have security protocols that keep data, applications, and application use separate. Also, because many tenants may opt for access to an MTS rather than maintain their own system, redundancy, up-time, and backup are additional functions that may be implemented in the MTS. In addition to user-specific data and tenant specific data, system  316  might also maintain system level data usable by multiple tenants or other data. Such system level data might include industry reports, news, postings, and the like that are sharable among tenants. 
         [0038]    In certain embodiments, user systems  312  (which may be client systems) communicate with application servers  400  to request and update system-level and tenant-level data from system  316  that may require sending one or more queries to tenant data storage  322  and/or system data storage  324 . System  316  (e.g., an application server  400  in system  316 ) automatically generates one or more SQL statements (e.g., one or more SQL queries) that are designed to access the desired information. System data storage  324  may generate query plans to access the requested data from the database. 
         [0039]    Each database can generally be viewed as a collection of objects, such as a set of logical tables, containing data fitted into predefined categories. A “table” is one representation of a data object, and may be used herein to simplify the conceptual description of objects and custom objects. It should be understood that “table” and “object” may be used interchangeably herein. Each table generally contains one or more data categories logically arranged as columns or fields in a viewable schema. Each row or record of a table contains an instance of data for each category defined by the fields. For example, a CRM database may include a table that describes a customer with fields for basic contact information such as name, address, phone number, fax number, etc. Another table might describe a purchase order, including fields for information such as customer, product, sale price, date, etc. In some multi-tenant database systems, standard entity tables might be provided for use by all tenants. For CRM database applications, such standard entities might include tables for Account, Contact, Lead, and Opportunity data, each containing pre-defined fields. It should be understood that the word “entity” may also be used interchangeably herein with “object” and “table”. 
         [0040]    In some multi-tenant database systems, tenants may be allowed to create and store custom objects, or they may be allowed to customize standard entities or objects, for example by creating custom fields for standard objects, including custom index fields. U.S. patent application Ser. No. 10/817,161, filed Apr. 2, 2004, entitled “Custom Entities and Fields in a Multi-Tenant Database System”, and which is hereby incorporated herein by reference, teaches systems and methods for creating custom objects as well as customizing standard objects in a multi-tenant database system. In certain embodiments, for example, all custom entity data rows are stored in a single multi-tenant physical table, which may contain multiple logical tables per organization. It is transparent to customers that their multiple “tables” are in fact stored in one large table or that their data may be stored in the same table as the data of other customers. 
         [0041]    Any of the above embodiments may be used alone or together with one another in any combination. Embodiments encompassed within this specification may also include embodiments that are only partially mentioned or alluded to or are not mentioned or alluded to at all in this brief summary or in the abstract. Although various embodiments may have been motivated by various deficiencies with the prior art, which may be discussed or alluded to in one or more places in the specification, the embodiments do not necessarily address any of these deficiencies. In other words, different embodiments may address different deficiencies that may be discussed in the specification. Some embodiments may only partially address some deficiencies or just one deficiency that may be discussed in the specification, and some embodiments may not address any of these deficiencies. 
         [0042]    Reference in the specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the invention. The appearances of the phrase “in one embodiment” in various places in the specification are not necessarily all referring to the same embodiment. 
         [0043]    While the invention has been described in terms of several embodiments, those skilled in the art will recognize that the invention is not limited to the embodiments described, but can be practiced with modification and alteration within the spirit and scope of the appended claims. The description is thus to be regarded as illustrative instead of limiting.