System and method for deadlock management in database systems with demultiplexed connections

A database management system (DBMS), wherein the DBMS includes a plurality of applications capable of requesting access to a plurality of database resources and capable of holding locks on the plurality of database resources, and an application scheduler for managing requests from the plurality of applications for access to database resources, the DBMS further comprising:

• a plurality of worker agents, the plurality of worker agents including a plurality of normal worker agents and overflow worker agents;
• and
• a deadlock detector coupled to the application scheduler for identifying a deadlock;
• wherein the application scheduler assigns one worker agent to an application requesting access to a database resource, assigns a flag to an application holding a lock on the database resource while disassociated from a worker agent, and in cooperation with the deadlock detector, resolves the deadlock between the application requesting access and the flagged application holding the lock.

A computer readable medium containing program instructions for managing requests for access to database resources in a database system, the database system comprising a plurality of applications capable of requesting access to a plurality of database resources and capable of holding locks on the plurality of database resources, the database system further comprising an application scheduler for managing requests from the plurality of applications for access to the plurality of database resources, the program instructions for:

• a) assigning a worker agent from a plurality of worker agents to an application by the application scheduler;
• b) identifying a deadlock via a deadlock detector coupled to the application scheduler, the deadlock being between an application disassociated from the worker agent while holding a lock on a database resource and another application requesting access to the database resource;
• and
• c) resolving the deadlock.

A method of deadlock management for a database system, the database system comprising a set of applications selectively requesting and holding locks on database resources, a pool of worker agents comprising normal worker agents and overflow worker agents, a wait queue, and a priority queue, the method comprising the steps of:

• marking an application with a flag value based on an existing application flag value and on a state of applications requesting and holding locks on database resources, comprising the steps of:
• marking an application with a flag value W where the application becomes disassociated from a worker agent and holds a lock on a database resource;
• marking an application with a flag value H where the application has a flag value W and where another application requests a lock on the database resource;
• marking an application with a flag value D where the application requests a worker agent, has a flag value H and there a normal worker agent or overflow worker agent is not available for the application;
• marking an application with the flag value Q where the application has a flag value W and a normal worker agent is not available upon request, the application being placed on the wait queue, and
• marking an application with the flag value D where the application has the flag value Q and another application requests a lock held by the application having the flag value Q;
• responding to an application request for a worker agent and selectively providing a normal worker agent, an overflow worker agent, or placing the application on the wait queue or on the priority queue, based on the application flag value, comprising the steps of:
• responding to a request for a worker agent from an application with flag value H by obtaining a normal worker agent if available and alternatively by providing an overflow worker agent, further comprising the step of placing the application on the priority queue where an overflow worker agent is not available, and
• responding to a request for a worker agent from an application with flag value W by obtaining a normal worker agent if available and alternatively by placing the application on the wait queue;
• clearing the application flag value when an application is provided with a worker agent;
• polling an application and declaring a deadlock where the application has a specified flag value and the application holds a lock on a database resource requested by another application, comprising the step of declaring a deadlock where an application has a flag value D and the application holds a lock on a database resource that is requested by another application, the database system further comprising a lock wait deadlock graph and a resource representation, the lock wait deadlock graph comprising means to represent applications requesting and holding locks on database resources whereby the step of declaring a deadlock comprises the step of determining if an application holds a lock requested by another application by accessing the lock wait graph, and
• selecting an application holding a lock and requiring the application to release the lock, following detection of a deadlock on the lock.

A deadlock management system for a database system, the database system comprising a set of applications selectively requesting and holding locks on database resources, a pool of worker agents comprising normal worker agents and overflow worker agents, an application scheduler, a wait queue, a priority queue, and a deadlock detector, the database system supporting an application holding a lock while disassociated from a worker agent, the deadlock management system comprising:

• means for marking an application with a flag value based on an existing application flag value and on a state of applications requesting and holding locks on database resources, comprising;
• means for marking an application with a flag value W where the application becomes disassociated from a worker agent and holds a lock on a database resource;
• means for marking an application with a flag value H where the application has a flag value W and where the database resource is requested by another application;
• means for marking an application with a flag value D where the application requests a worker agent, has a flag value H and a normal worker agent or overflow worker agent is not available for the application;
• means for marking an application with the flag value Q where the application has a flag value W and a normal worker agent is not available upon request, wherein the application is placed on the wait queue;
• and
• means for marking an application with the flag value D where the application has the flag value Q and another application requests a lock held by the application having the flag value Q;
• means for the application scheduler to respond to an application request for a worker agent from the pool and to selectively provide a normal worker agent, an overflow worker agent, or place the application on the wait queue or on the priority queue, based on the application flag value, comprising:
• means for responding to a request for a worker agent from an application with flag value H by obtaining a normal worker agent if available and alternatively providing an overflow worker agent, further comprising means for placing the application on the priority queue where an overflow worker agent is not available;
• and
• means for responding to a request for a worker agent from an application with flag value W by obtaining a normal worker agent if available and alternatively by placing the application on the wait queue;
• means for clearing the application flag value when an application is provided with a worker agent,
• means for the deadlock detector to poll an application;
• and
• means for the deadlock detector to declare a deadlock where the application has a specified flag value and the application holds a lock on a database resource requested by another application;
• comprising:
• means for declaring a deadlock where an application has a flag value D and the application holds a lock on a database resource that is requested by another application,
• the deadlock detector further comprising a lock wait deadlock graph and a resource representation, the lock wait deadlock graph comprising means to represent applications requesting and holding locks on database resources whereby the deadlock detector determines if an application holds a lock requested by another application;
• and
• means to select an application holding a lock and to require the application to release the lock, following detection of a deadlock on the lock.

A method for managing requests for access to database resources in a database system, the database system comprising a plurality of applications capable of requesting access to a plurality of database resources and capable of holding locks on the plurality of database resources, and the database system further comprising an application scheduler for managing requests from the plurality of applications for access to database resources, the method comprising the steps of:

• a) assigning a worker agent from a plurality of worker agents to an application by the application scheduler, wherein the plurality of worker agents includes normal worker agents and overflow worker agents, and assigning step a) further includes:
• (a1) marking an application with a flag value based on an existing application flag value and on a state of applications requesting and holding locks on database resources, wherein the marking step includes:
• marking an application with a flag value W where the application becomes disassociated from a worker agent and holds a lock on a database resource;
• marking an application with a flag value H where the application has a flag value W and the database resource is requested by another application;
• marking an application with a flag value D where the application requests a worker agent, has a flag value H and there a normal worker agent or overflow worker agent is not available for the application;
• marking an application with the flag value Q where the application has the flag value W and a normal worker agent is not available upon request, wherein the application is placed on a wait queue, and
• marking an application with the flag value D where the application has the flag value Q and another application requests a lock held by the application having the flag value Q;
• and
• (a2) assigning a normal worker agent or an overflow worker agent to the application, or placing the application on a wait queue or on a priority queue, based on the application flag value;
• b) identifying a deadlock via a deadlock detector coupled to the application scheduler, the deadlock being between an application disassociated from the worker agent while holding a lock on a database resource and another application requesting access to the database resource, wherein identifying step (b) further includes:
• (b1) polling an application;
• and
• (b2) declaring a deadlock where the application has a specified flag value and the application holds a lock on a database resource requested by another application;
• and
• c) resolving the deadlock.

A database management system (DBMS), wherein the DBMS includes a plurality of applications capable of requesting access to a plurality of database resources and capable of holding locks on the plurality of database resources, and an application scheduler for managing requests from the plurality of applications for access to database resources, the DBMS further comprising:

• a plurality of worker agents, the plurality of worker agents including a plurality of normal worker agents and overflow worker agents;
• a deadlock detector coupled to the application scheduler for identifying a deadlock;
• wherein the application scheduler assigns one worker agent to an application requesting access to a database resource, assigns a flag to an application holding a lock on the database resource while disassociated from a worker agent, and in cooperation with the deadlock detector, resolves the deadlock between the application requesting access and the flagged application holding the lock;
• means for marking an application with a flag value based on the existing application flag value and on the state of applications requesting and holding locks on database resources;
• means for the application scheduler to respond to the application requesting access and to selectively assign a normal worker agent, an overflow worker agent, or place the application on a wait queue or on a priority queue, based on the application flag value;
• means for clearing the application flag value when an application is provided with a worker agent;
• wherein the deadlock detector further includes:
• means for polling an application and means for declaring a deadlock where the application has a specified flag value, and the application holds a lock on a database resource requested by another application;
• and
• wherein the means for marking an application comprises:
• means for marking an application with a flag value W where the application becomes disassociated from a worker agent and holds a lock on a database resource:
• means for marking an application with a flag value H where the application has a flag value W and where another application requests access to the locked database resource;
• means for marking an application with a flag value D where the application requests a worker agent, has a flag value H and a normal worker agent or overflow worker agent is not available for the application;
• means for marking an application with the flag value Q where the application has the flag value W and a normal worker agent is not available upon request, wherein the application is placed on the wait queue;
• and
• means for marking an application with the flag value D where the application has the flag value Q and another application requests a lock held by the application having the flag value Q.

A computer readable medium containing program instructions for managing requests for access to database resources in a database system, the database system comprising a plurality of applications capable of requesting access to a plurality of database resources and capable of holding locks on the plurality of database resources, the database system further comprising an application scheduler for managing requests from the plurality of applications for access to the plurality of database resources, the program instructions for:

• a) assigning a worker agent from a plurality of worker agents to an application by the application scheduler, wherein the plurality of worker agents includes normal worker agents and overflow worker agents, and assigning instruction a) further includes:
• (a1) marking an application with a flag value based on an existing application flag value and on a state of applications requesting and holding locks on database resources, wherein the marking instruction (a1) comprising the instructions for:
• marking an application with a flag value W where the application becomes disassociated from a worker agent and holds a lock on a database resource;
• marking an application with a flag value H where the application has a flag value W and the database resource is requested by another application;
• marking an application with a flag value D where the application requests a worker agent, has a flag value H and there a normal worker agent or overflow worker agent is not available for the application;
• marking an application with the flag value Q where the application has the flag value W and a normal worker agent is not available upon request, wherein the application is placed on a wait queue, and
• marking an application with the flag value D where the application has the flag value Q and another application requests a lock held by the application having the flag value Q;
• and
• (a2) assigning a normal worker agent or an overflow worker agent to the application, or placing the application on a wait queue or on a priority queue, based on the application flag value;
• b) identifying a deadlock via a deadlock detector coupled to the application scheduler, the deadlock being between an application disassociated from the worker agent while holding a lock on a database resource and another application requesting access to the database resource, wherein identifying instruction (b) further includes:
• (b1) polling an application;
• and
• (b2) declaring a deadlock where the application has a specified flag value and the application holds a lock on a database resource requested by another application;
• and
• c) resolving the deadlock.