Patent Publication Number: US-6904431-B2

Title: Algorithm for dynamic selection of data locking granularity

Description:
FIELD OF THE INVENTION 
   The present invention pertains to database technology. More particularly, the present invention relates to improving database concurrency while minimizing a possibility of a deadlock. 
   BACKGROUND OF THE INVENTION 
   Present technology allows multiple users to access one set of data via a network. Capability to access simultaneously large bodies of message data improves the efficiency of this technological development. 
   In order to maintain data integrity, no two users may modify data, for example message data in an email system, at the same time. The present technology utilizes locks to serialize data access to one user at a time. To promote the most concurrent access to message data, locks are placed with the finest granularity practical. The difficulty with placing extremely fine grained locks, for example locks on every word of a message data, is the need for single processing entities to obtain and hold multiple locks during the processing of a message. If the granularity of locks within a message system is too fine grained, this leads to deadlock situations. 
   A deadlock is a case where one thread of processing holds a lock and, at the same time, requires a lock held by another thread. In addition to holding the lock that the first thread requires, the second thread, in turn, requires the lock that the first thread holds. Without external intervention, this is an unresolvable situation where the processing of neither thread can progress. In addition, deadlock detection and external intervention slows message processing considerably, thus making the deadlock detection process inefficient. 
   A goal of the idealized message processing then is to minimize deadlock conditions, while allowing many threads of processing to access message data or message data infrastructure at the same time, thus improving data concurrency. 
   SUMMARY OF THE INVENTION 
   A method and apparatus for improving database concurrency are described. The method may comprise receiving a request to access data, determining a data locality within a database utilizing unique data keys, determining a data locking level based on a deadlock history corresponding to the data locality, and providing access to the data while locking part of the database based on the data locking level. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention is illustrated by way of example and not limitation in the figures of the accompanying drawings, in which like references indicate similar elements and in which: 
       FIG. 1  illustrates an exemplary network architecture in which an embodiment of the present invention may be implemented; 
       FIG. 2  illustrates components of a data locking module according to one embodiment of the present invention; 
       FIG. 3  illustrates components of a backend data store layer according to one embodiment of the present invention; 
       FIG. 4  illustrates components of a user&#39;s data database according to one embodiment of the present invention; 
       FIG. 5  is a flow diagram showing a process of determining a data locking level within a database according to one embodiment of the present invention; 
       FIG. 6  illustrates a processing system according to one embodiment of the present invention. 
   

   DETAILED DESCRIPTION 
   An algorithm for improving database concurrency is described. Note that in this description, references to “one embodiment” or “an embodiment” mean that the feature being referred to is included in at least one embodiment of the present invention. Further, separate references to “one embodiment” in this description do not necessarily refer to the same embodiment; however, neither are such embodiments mutually exclusive, unless so stated and except as will be readily apparent to those skilled in the art. Thus, the present invention can include any variety of combinations and/or integrations of the embodiments described herein. 
   Exemplary Architecture 
     FIG. 1  illustrates an architecture in which a method and apparatus of the present invention may be implemented according to one embodiment of the invention. A user may access a server access application  105  that may run on a client machine  100 . The server access application  105 , e.g. an email client, may provide the user with access to content located on a server  120 , which the user may specify via a user interface  110 . The server  120  may contain a backend data store  130  comprising data that the user may wish to obtain access to. The backend data store  130  may contain user&#39;s data, e.g. email messages,  310  database and deadlock history  315  database illustrated in FIG.  3 . The server  120  may also contain a data locking module  125 . The components of the data locking module are illustrated in FIG.  2 . In the illustrated embodiment the data locking module  200  contains a data locator  205 , a deadlock analysis module  210  and a hashing module  215 . The functions of the data locking module  200  and its components will be described in detail in the following description. 
   The physical processing systems which embody the server  120  and the client  100  may include processing systems such as conventional personal computers (PCs) and/or server-class computer systems according to one embodiment of the invention.  FIG. 6  illustrates an example of such a processing system at a high level. The processing system of  FIG. 6  may include one or more processors  600 , read-only memory (ROM)  610 , random access memory (RAM)  620 , and a mass storage device  630  coupled to each other on a bus system  640 . The bus system  640  may include one or more buses connected to each other through various bridges, controllers and/or adapters, which are well known in the art. For example, the bus system  640  may include a ‘system bus’, which may be connected through an adapter to one or more expansion busses, such as a peripheral component interconnect (PCI) bus or an extended industry standard architecture (EISA) bus. Also coupled to the bus system  640  may be the mass storage device  630 , one or more input/output (I/O) devices  650  and one or more data communication devices  660  to communicate with remote processing systems via one or more communication links  665  and  670 , respectively. The I/O devices  550  may include, for example, any one or more of a display device, a keyboard, a pointing device (e.g., mouse, touchpad, trackball), an audio speaker. 
   The processor(s)  600  may include one or more conventional general-purpose or special-purpose programmable microprocessors, digital signal processors (DSPs), application specific integrated circuits (ASICs), or programmable logic devices (PLD), or a combination of such devices. The mass storage device  630  may include any one or more devices suitable for storing large volumes of data in a non-volatile manner, such as magnetic disk or tape, magneto-optical storage device, or any of various types of Digital Video Disk (DVD) or Compact Disk (CD) based storage or a combination of such devices. 
   The data communication device(s)  660  each may be any devices suitable for enabling the processing system to communicate data with a remote processing system over a data communication link, such as a wireless transceiver or a conventional telephone modem, a wireless modem, an Integrated Services Digital Network (ISDN) adapter, a Digital Subscriber Line (DSL) modem, a cable modem, a satellite transceiver, an Ethernet adapter, or the like. 
   Methodology 
   With these concepts in mind an embodiment of the present invention can be further explored with reference to FIG.  5 .  FIG. 5  shows a process of dynamically determining a data locking level. At  510  a user may log-in into an email system via the server access application  105  that may be executed on the client machine  100 . The server access application  105  may be, for example, a Microsoft Outlook email server provided by Microsoft Corporation of Redmond, Washington or Eudora email server provided by Qualcomm Inc. of San Diego, Calif. The server access application  105  provides the user with the user interface  110  to facilitate a user-friendly access to the server  120 , which in one embodiment is a mail server. In one embodiment, the server access application  105  prompts the user via the user interface  110  to enter his/her user name and password in order to log-in into an email system located on the server  120 . Upon the user logging into the system, the identification data is transmitted to the server  120 . Upon receiving the identification data the server  120  verifies the user&#39;s authenticity, and if the identification is confirmed, the user is provided with access to the email system located on the mail server. The techniques for verifying the user&#39;s identity are well known in the art and do not require any further explanation. 
   At  510  after obtaining access to the email system the user may specify a mailbox that he/she would like to access. In one embodiment the user may have a number of different mailboxes. For example, the user may have an inbox mailbox that may contain the user&#39;s new and already read relevant email messages. The user may also have a junk mailbox that may contain spam email that may be filtered according to some predetermined rules. The user may also have a trash mailbox containing messages that the user previously deleted. In one embodiment if the user does not specify which mailbox to access, the user is provided with default mailbox that may be the inbox mailbox. 
   At  515  of  FIG. 5  the data locator  205  of the data locking module  200  illustrated in  FIG. 2  determines the location of the user-specified data, which may include a particular mailbox, an email message within a particular mailbox, or a number of email messages within a particular mailbox. In one embodiment every user of the email system is assigned a unique user identifying key. The unique user identifying key may be a unique text string corresponding to a user name, a user password, or combination of both. In one embodiment the unique user identifying key is the user&#39;s email address. It will be appreciated that there may be other techniques for developing and assigning a unique user identifying key to every user of the email system. 
   In one embodiment of the present invention the backend data store  330  of  FIG. 3  contains a number of database files located in the user&#39;s data  310  database, that may be accessed utilizing unique user identifying keys. In one embodiment hashing may be used to determine a database file corresponding to the user requesting an access to his/her email data. Each database file may contain data corresponding to a number of users according to some predetermined data distribution rules. For example, the data may be distributed between the database files based on a first letter of a user&#39;s name. One example of such a data distribution is shown in  FIG. 4 , where a database file  415  contains data of users whose last name starts with letters ‘a’ through ‘k’, a database file  420  contains data of users whose last name starts with letters ‘l’ through ‘q’, and a database file  425  contains data of users whose last name starts with letters ‘r’ through ‘z’. 
   Upon determining a database file which contains data corresponding to the user, the data locator  205  determines a location of the requested data within the file, i.e. data locality. In one embodiment, the data locator  205  after locating the data within the database file that pertains to the user, locates the user-specified mailbox or the user-specified email message within the user-specified mailbox. In one embodiment every mailbox and every email message within every mailbox are assigned a unique identification keys that may be utilized to determine the location of the requested data within a data file. In one embodiment hashing algorithms may be utilized along with the unique identification keys to determine the requested data locality. 
   Upon locating the requested data within a data file containing data corresponding to the user, the deadlock analysis module  210  at  530  of  FIG. 5 , in order to ensure data consistency and data concurrency in the database, determines a level of data locking to be applied by accessing a deadlock history database  315 . In one embodiment the deadlock history database  315  contains information about previous deadlocks occurred during a predetermined time interval that involved data located within a single database file. The deadlock history database  315  may also contain a number of successful message data requests without a deadlock from the database file during a predetermined time interval. The entries of the deadlock history database  315  corresponds to each data locality. In one embodiment the data locality is defined as a database object within a database file and the deadlock history information is kept for every database object within a database file. In another embodiment the data locality is defined as a database page and the deadlock history information is kept for every database page within a database file. In yet another embodiment the data locality is defined as a database row and the deadlock history information is kept for every database row within a database file. It will be appreciated that neither the data locality definition nor the deadlock history database design is limited to the examples presented above and may be defined and designed to accommodate the system&#39;s needs, data and size in order to reduce data overhead occurring due to maintenance of deadlock information in the database. 
   In one embodiment of the present invention, hashing is utilized to determine the locality of the user-requested data within a database file. The hashing module  215  may determine the locality of data by utilizing a hashing algorithm and unique keys assigned to the users of the email system and to the email data. In one embodiment the unique message identification key and mailbox identification key are hashed and utilized as an index into a selected database file. In addition, the unique user identification key may be hashed and used as an index to determine a database file containing data corresponding to the user. Hashing algorithms and hashing techniques are well known in the art and do not require further explanation. 
   In one embodiment of the present invention the deadlock analysis module  210  determines the level of data locking based on the deadlock history information stored in the deadlock history database  315 . Upon retrieving the data history information corresponding to the data locality of the user requested data, the deadlock analysis module  210  uses a predetermined deadlock threshold levels to determine the level of locking. In one example if the number of deadlocks for a particular data locality occurred during a predetermined time interval is greater than a number of the allowed deadlocks represented by a high deadlock threshold, the data will be locked more conservatively. If the number of deadlocks for a particular data locality during a predetermined time interval is less than the number of the allowed deadlocks, then a less conservative data locking approach may be used. For example, if the number of the allowed deadlocks is 6 deadlocks in 10 minutes, and the number of deadlocks which actually occurred in the last 10 minutes involving the data locality corresponding to the user-requested data (e.g. an email message in an inbox mailbox) is 7 deadlocks, the inbox mailbox containing the user-requested email message may be locked from access of other users to ensure data consistency. However, if the information retrieved from the deadlock history database  315  indicates that there were no deadlocks that occurred involving the requested email message in the last 10 minutes, only the user-requested email message may be locked from access by other users, thus allowing other users to access the mailbox containing the requested message, which is providing a higher level of data concurrency. The deadlock history database  315  may be updated upon an occurrence of a deadlock in the system. 
   In one embodiment of the present invention the data locking levels are database file locking level, database record locking level, database page locking level, database row locking level and database object locking level. It will be appreciated that the data locking levels are not limited to the ones listed above. 
   In one embodiment the data locking method is utilized when the user is attempting to perform a writing operation, examples of which may be removing an email message from a mailbox; adding a new mailbox; moving messages from one mailbox to another; changing a parameter, which is utilized to distribute users&#39; data among database files, for example changing user&#39;s last name. The determination of the data locking level is performed dynamically upon the user specifying the data to be accessed. 
   It will be appreciated that the above described method and apparatus are not limited to email systems and may be utilized with any data that may be represented by a unique identification keys. For example, the above described method and apparatus may be utilized in databases including electronic pager or instant message data, digitally stored video or image information, etc. 
   It will also be appreciated that the present invention is not limited to traditional client-server systems and may be implemented in other environments, such as peer-to-peer systems or in non-network environments. 
   In addition, it will be recognized that many of the features and techniques described above may be implemented in software. For example, the described operations may be carried out in the server  120  or other suitable device in response to its processor(s) executing sequences of instructions contained in memory of the device. The instructions may be executed from a memory such as TAM 73 and may be loaded from a persistent store, such as a mass storage device, and/or from one or more other remote processing systems. Likewise, hardwired circuitry may be used in place of software, or in combination with software, to implement the features descried herein. Thus, the present invention is not limited to any specific combination of hardware circuitry and software, nor to any particular source of software executed by the processing systems. 
   Thus, a method and apparatus for improving database concurrency have been described. Although the present invention has been described with reference to specific exemplary embodiments, it will be evident that various modifications and changes may be made to these embodiments without departing from the broader spirit and scope of the invention as set forth in the claims. Accordingly, the specification and drawings are to be regarded in an illustrative sense rather than a restrictive sense.