Abstract:
A method, system and article of manufacture for reducing a deadlock probability during transaction processing in a computer network system having a plurality of users of the network system that comprises a content management system performing implicit transactions via API calls to a library server on a plurality of entities shareable by users of the network. The computer-implemented method comprises invoking a transaction sequence in response to a transaction request, performing a prepare portion of the transaction sequence, implicitly committing the prepare portion of the transaction, performing an update portion of the transaction sequence, and fully committing the transaction.

Description:
BACKGROUND OF THE INVENTION 
   The invention pertains to the problem of potential database deadlocks or timeouts due to the locking of resources during transactions, on a content management (CM) system in particular. Databases store data in a variety of manners depending on the internal organization. For example, a relational database system, typically stores data in tables. The tables are comprised of rows, each of which contains a record. The record, in turn, contains entities and the entities contain the actual related data values for a data “object.” Each table may also be associated with one or more indexes, which provide rapid access to the rows in an order determined by the index and based on key data values contained in selected entities in each row. As an example, a row might be associated with each employee of an organization and contain entities that hold such information as the employee name, an identification number, and telephone numbers. One index might order the rows numerically by employee identification number, while another index might order the rows alphabetically by employee name. 
   Such a database conventionally includes methods which insert and delete rows and update the information in a row. When changes are made to the rows, any database indexes associated with the table may also need to be updated in order to keep the indexes synchronized with the tables. The rows in each table are mapped to a plurality of physical pages on the disk to simplify data manipulation. Such an arrangement is illustrated in  FIG. 1 . 
   In  FIG. 1 , table  10 , which illustratively consists of rows  12 ,  14 ,  16 , and  18 , is mapped to a chain of pages of which pages  20 ,  22 , and  24  are shown. In the table illustrated, each row consists of five separate entities. For example, row  12  consists of entities  26 ,  28 ,  30 ,  32  and  34 . The entities in each of rows  12 ,  14 ,  16  and  18  are mapped illustratively to page  22  which can contain data for more than one row. For example, entity  26  maps to location  36  in page  22 . Entity  28  maps to location  38 . Entity  30  maps to location  40 . In a similar manner entity  32  maps to location  42  and entity  34  maps to location  44 . The entities in the next row  14  are mapped directly after the entities in row  12 . For example, entity  46  is illustrated and maps to page location  48 . When the page is completely filled with data, entity information is mapped to the next page in the page chain. The pages are chained together by means of page pointers. For example, page pointer  50  links pages  20  and  22 , whereas page pointer  52  links pages  22  and  24 . All of the pages used to store the data in table  10  are linked together in a similar manner in a page chain. 
   The data pages are normally kept in a page buffer pool located in system memory. In order to make such a database system persistent or “durable”, the data pages must be written to an underlying non-volatile storage system, such as a disk storage. This storage operation takes place on a page level so that when a modification is made to data on a page the entire page is stored in the persistent storage. Each page could be copied to the persistent storage as soon as data on the page was modified. However, this immediate copying greatly slows the system operation since persistent storage is generally much slower than RAM memory. Alternatively, the information in modified pages in the buffer pool can be copied or “flushed” to the disk storage at intervals. For example, the information could be flushed periodically or when the number of changed pages in the buffer pool reaches some predetermined threshold. During this disk flushing operation, the data modifications are performed “in place” so that the old data is either overwritten or deleted from the disk and lost. 
   Since the data is lost during the modification process, in order to ensure data integrity in the case of a system failure, or crash, the actions performed on the database are grouped into a series of “transactions”. Each transaction is “atomic” which means that either all actions in the transaction are performed or none are performed. The atomic property of a transaction ensures that the transaction can be aborted or “rolled back” so that all of the actions which constitute the transaction can be undone. Database transactions commonly have a “commit” point at which time it can be guaranteed that all actions which comprise the transaction will complete properly. If the transaction does not reach the commit point, then it will be rolled back so that the system can return to its state prior to the initiation of the transaction. Consequently, if there is a system termination or crash prior to the commit point, the entire transaction can be rolled back. 
   The use of a buffer pool complicates transaction processing because even though a transaction has committed, system operation could terminate after a page has been modified, but before the modified page is flushed to disk. In order to prevent data loss caused by such a system interruption, a logging system is used to permit data recovery. The logging system records redo and undo information for each data modification in a special file called a “recovery log” that is kept in non-volatile storage. 
   During the processing of a CM transaction, it is to be appreciated that locks are placed on database pages and resources so that a second concurrent CM transaction does not replace entities, unknown to the first CM transaction, before the first CM transaction has modified selected entities and performed a write operation for those modifications. Additionally, many systems maintain add the restriction that all write locks created by a CM transaction should be held until the transaction commits. 
   A problem that arises with CM transaction schedulers is that transactions can get involved in deadlocks or can time-out waiting for a resource to be released from a lock. CM transactions sometimes have to wait for locks where such waiting is caused by another transaction holding a conflicting lock, and the waiting transaction cannot make any progress until the other transaction releases its lock. If two CM transactions are waiting for each other, neither can make progress until the other one releases its lock. As long as neither of them releases its lock, the two transactions are deadlocked. More generally, deadlocks can involve more than two CM transactions that are waiting for each other in a cyclic way. 
   Therefore, it is desirable to provide a method and apparatus which can reduce the potential for deadlocks and time-outs caused by resource locking, particularly in a high volume CM system. 
   The present invention therefore provides a solution to the aforementioned problems, and offers other advantages over the prior art. 
   BRIEF SUMMARY OF THE INVENTION 
   In accordance with the present invention, there is provided a method of reducing a deadlock probability during transaction processing of a user-requested transaction in a computer network system having a plurality of users of the network system. The computer network system comprises a content management system performing implicit transactions via API calls to a library server on a plurality of entities shareable by users of the network. The method comprises invoking a transaction sequence in response to a transaction request, performing a prepare portion of the transaction sequence, implicitly committing the prepare portion of the transaction, performing an update portion of the transaction sequence, and fully committing the transaction. 
   In accordance with another aspect of the present invention, there is provided a computer network system having a plurality of users of the network system, the system comprising a content management system, configured to process transaction requests from the users and running on the computer network system, a means for invoking a transaction sequence in response to a transaction request, a means for performing a prepare portion of the transaction sequence, a means for implicitly committing the prepare portion of the transaction, a means for performing an update portion of the transaction sequence, and a means for fully committing the transaction. 
   In accordance with yet another aspect of the present invention, there is provided an article of computer-readable media having contents that cause a content management system running on a computer network system to perform the computer-implemented steps of invoking a transaction sequence in response to a transaction request bu a user, performing a prepare portion of the transaction sequence, implicitly committing the prepare portion of the transaction, performing an update portion of the transaction sequence, and fully committing the transaction. 
   One benefit obtained from the present invention is the reduction in time that system resources are in a locked state. 
   Another benefit obtained from the present invention is the reduction in the possibility of a deadlock between separate transactions, each waiting for a locked resource the other transaction holds. 
   Yet another benefit obtained from the present invention is the reduction in the possibility of a time-out occurring when a transaction is waiting for a locked resource. 
   Other benefits and advantages of the subject method and system will become apparent to those skilled in the art upon a reading and understanding of this specification. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention may take physical form in certain parts and steps and arrangements of parts and steps, the preferred embodiments of which will be described in detail in the specification and illustrated in the accompanying drawings hereof and wherein: 
       FIG. 1  is an abstracted block diagram illustrating rows in a database table mapped to a plurality of physical pages on a disk; 
       FIG. 2  is a block diagram of a network-connected content management system in accordance with a preferred embodiment of the present invention; 
       FIG. 3  is a flowchart of a prior art API sequence that does not commit an implicit transaction until entities in both a library server and a resource manager are updated to the database; and 
       FIG. 4  is a flowchart for an API sequence according to a preferred embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Reference will now be made in detail to the preferred embodiment of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to like elements throughout. 
   The detailed description which follows is presented in terms of general procedures, steps and symbolic representations of operations of data bits within a computer memory, associated computer processors, networks, and network devices. These procedure descriptions and representations are the means used by those skilled in the data processing art to convey the substance of their work to others skilled in the art. A procedure is here, and generally, conceived to be a self-consistent sequence of steps or actions leading to a desired result. Thus, the term “procedure” is generally used to refer to a series of operations performed by a processor, be it a central processing unit of a computer, or a processing unit of a network device, and as such, encompasses such terms of art as “objects,” “functions,” “subroutines” and “programs.” 
   The procedures presented herein are not inherently related to any particular computer or other apparatus. In particular, various general purpose machines may be used with programs in accordance with the teachings herein, or it may prove more convenient to construct more specialized apparatus to perform the required method steps. 
   However, one of ordinary skill in the art will recognize that there exists a variety of platforms and languages for creating software for performing the procedures outlined herein. One of ordinary skill in the art also recognizes that the choice of the exact platform and language is often dictated by the specifics of the actual system constructed, such that what may work for one type of general purpose computer may not be efficient on another type of general purpose computer. 
   One of ordinary skill in the art to which this invention belongs will have a solid understanding of content management systems, database management systems, and methods of securely controlling access to entities managed by the content management system such as an access control list (ACL) in particular. It being recognized that such practitioners do not require specific details of the software, but rather find data structure descriptions and process descriptions more desirable (due to the variety of suitable hardware and software platforms), such specifics are not discussed to avoid obscuring the invention. 
     FIG. 2  is a block diagram of a network connected content management system in accordance with a preferred embodiment of the present invention. The system shown in  FIG. 2  is particularly suited to delivery of content over a network or the Internet. A content management system  60  is running on a server computer  62  which is connected to a network  64 . One or more users  66  of the CMS  60  access controlled entities on a content database  68 , such as a DB2 database for instance, by communicating with the CMS  60  via the network  64 . The CMS  60  is in communication with a library server (LS)  70 , a resource manager (RM)  72  and a database management system (DBMS)  74 . The DBMS  74  utilizes a page cache buffer  76  residing in server  62  random access memory (RAM) for buffering database pages retrieved from and being written to the database  68 . The CMS  60 , LS  70 , RM  72  and the DBMS  74  are shown in the figure as running on the same server  62 , however, it is to be appreciated that some or all of these may be running on separate, network-connected, computers. 
   On the system illustrated, a CM transaction is defined as a work unit for a single user, although the CM system  60  can be concurrently processing multiple transactions for multiple users  66 . In a preferred embodiment, a CM transaction consists of a sequence of application program interface (API) calls made through a single connection  78  to the LS  70 . If any API call fails in the intermediate portion of a transaction, all of the database entities are rolled back to their respective original states at the beginning of the transaction. 
   There are two categories of CM transactions, namely explicit transactions and implicit transactions. Explicit transactions are controlled by the user  66  who starts and ends the explicit transaction, either committing or rolling back the transaction as a final step. An implicit transaction is one where the invoking user wishes to perform a single-item creation, update or deletion on the database  68 , and desires to have the transaction automatically committed upon completion, without the necessity of explicitly committing the transaction via a separate API call. 
   In an exemplary prior art CM system, the API does not commit the implicit transaction until entities in both the LS  70  and the RM  72  are updated to the database  68 . A corresponding sequence of processing steps is shown in  FIG. 3 . At processing step  100 , the API creates or updates, depending on the transaction type, an entity in the LS  70  with LS attributes and RM default information for an associated object. At step  102 , the API stores or replaces the object associated with the entity in the RM  72 . At step  104 , the API updates the entity with the correct RM information for the associated object. Finally, at step  106 , the API commits the transaction. 
   The above-described API sequence, however, introduces the undesirable possibility of deadlocks or time-outs as previously described. Thus, in the preferred embodiment, a new API sequence is provided to reduce the probability of deadlocks or time-outs. The new sequence also resolves a situation where a user retrieves an entity which has either default or correct object information with an uncommitted read (UR) from the LS  70  and the object cannot be found in the RM  72 . Because, at a prepare step, there is yet no entry in the user table, and another transaction cannot find both the entity on the LS side and the object on the RM side. An item is not physically created or updated until the associated object has been stored or replaced in the RM  72 . 
   With reference now to  FIG. 4 , a new API sequence of the preferred embodiment is provided. At processing step  110 , the API invokes a begin-transaction command to prepare the system for processing a new transaction. The functions performed by this step in the API sequence is dependent on the particular computer, and the particular operating system (OS) on which the CM system is running. There begin-transaction functions are well known in the art. The API then prepares to create or update an entity in the LS  70  by performing the prepare step  112  comprising: step  114  where the LS  70  checks the respective user privileges and generates a transaction ID, item ID, version ID and an object security token, step  116  where the LS  70  saves the information from the prior step in a system item table (not shown) and a system transaction table (not shown), step  118  where the LS  70  sets an in-progress flag on if the transaction is a create transaction, and step  120 , where the LS  70  returns the data required to access the RM  72  to the API. The above-described steps are each well known in the art and describe typical steps necessary for the processing of a user-requested transaction. 
   Subsequent to the above-described prepare step  112 , in various embodiments of the present invention, the LS  70  commits the transaction implicitly at step  122 , thus freeing locked resources, reducing the possibility of deadlock or time-out for other concurrent transactions. The implicit commit is performed in a transparent manner with respect to the user. The user is aware that the results of the transaction will be committed (hardened) at the successful completion of the transaction, however, the intermediate implicit commit of the present invention is not made known to the user, and the user is unaffected by it, except for performance improvements. At step  124 , the API stores or replaces the object associated with the entity in the RM  72 . Following this, at step  126  the API creates or updates the entity with LS attributes and RM information for the associated object wherein: the LS  70  parses user inputs to be stored in a user table (not shown) at step  128 , the LS invokes a generated access module to store values for LS system attributes, user attributes and RM attributes associated with the transaction at step  130 , and the LS  70  returns an OK status to the API at step  132 . 
   The API finally commits the entire transaction at step  134  after receiving the OK status from the LS at step  132  thus removing any remaining deadlock or time-out possibilities. 
   The invention has been described with reference to the preferred embodiments. Potential modifications and alterations will occur to others upon a reading and understanding of the specification. It is our intention to include all such modifications and alterations insofar as they come within the scope of the appended claims, or the equivalents thereof.