Managing checkpoint queues in a multiple node system

A computer executable method for recovering after a failure of one or more nodes of a multiple-node system, the method comprising the steps of:

• determining whether the failure involves only one node;
• and
• if the failure involves only said one node, then performing recovery by applying a recovery log of said node beginning at a first point in the recovery log;
• and
• if the failure involves one or more nodes in addition to said one node, then performing recovery by applying said recovery log of said node beginning at a second point in the recovery log;
• wherein said first point is different from said second point.

A computer executable method for recovering after a failure of one or more nodes of a multiple-node system, the method comprising the steps of:

• if it is unclear whether a particular version of a data item has been written to disk, then performing the steps of without attempting to recover said data item, marking dirtied cached versions of said data item that would have been covered if said particular version was written to disk;
• when a request is made to write one of said dirtied cached versions to disk, determining which version of said data item is already on disk;
• and
• if said particular version of said data item is already on disk, then not writing said one of said dirtied cached versions to disk.

A computer executable method for recovering a current version of a data item after a failure of one or more nodes in a system that includes multiple caches, the method comprising the steps of:

• modifying the data item in a first node of said multiple caches to create a modified data item;
• sending the modified data item from said first node to a second node of said multiple caches without durably storing the modified data item from said first node to persistent storage;
• after said modified data item has been sent from said first node to said second node and before said data item in said first node has been covered by a write-to-disk operation, discarding said data item in said first node;
• after said failure, reconstructing the current version of said data item by applying changes to the data item on persistent storage based on merged redo logs associated with all of said multiple caches;
• maintaining, for each of said multiple caches, a globally-dirty checkpoint queue and a locally-dirty checkpoint queue;
• wherein the globally-dirty data items associated with entries in the globally-dirty checkpoint queue are not retained until covered by write-to-disk operations;
• determining, for each cache, a checkpoint based on a lower of a first-dirtied time of the entry at the head of the locally-dirty checkpoint queue and the first-dirtied time of the entry at the head of the globally-dirty checkpoint queue;
• and
• after said failure, determining where to begin processing the redo log associated with each cache based on the checkpoint determined for said cache.

A computer executable method for recovering a current version of a data item after a failure of one or more nodes in a system that includes multiple caches, the method comprising the steps of:

• modifying the data item in a first node of said multiple caches to create a modified data item;
• sending the modified data item from said first node to a second node of said multiple caches without durably storing the modified data item from said first node to persistent storage;
• after said modified data item has been sent from said first node to said second node and before said data item in said first node has been covered by a write-to-disk operation, discarding said data item in said first node;
• and
• after said failure, reconstructing the current version of said data item by applying changes to the data item on persistent storage based on merged redo logs associated with all of said multiple caches;
• maintaining, for each of said multiple caches, a globally-dirty checkpoint queue and a locally-dirty checkpoint queue;
• wherein the globally-dirty data items associated with entries in the globally-dirty checkpoint queue are not retained until covered by write-to-disk operations;
• maintaining, for each cache, a first checkpoint record for the locally-dirty checkpoint queue that indicates a first time, where all changes made to data items that are presently dirty in the cache prior to the first time have been recorded on a version of the data item that is on persistent storage;
• maintaining, for each cache, a second checkpoint record for the globally-dirty checkpoint queue, wherein the second checkpoint record includes a list of data items that were once dirtied in the cache but have since been transferred out and not written to persistent storage;
• and
• after said failure, determining where to begin processing the redo log associated with each cache based on the first checkpoint record and said second checkpoint record for said cache.

A computer-readable medium carrying instructions for managing information about where to begin recovery after a failure of one or more nodes of a multiple-node system, the instructions comprising instructions for performing the steps of:

• in a particular node of a multiple-node system, maintaining both
• a single-failure queue that indicates where within a recovery log to begin recovery after a failure of said node, and
• a multiple-failure queue that indicates where within said recovery log to begin recovery after a failure of said node and one or more other nodes in said multiple-node system;
• in response to a dirty data item being written to persistent storage, removing an entry for said data item from both said single-failure queue and said multiple-failure queue;
• and
• in response to a dirty data item being sent to another node of said multiple-node system without first being written to persistent storage, removing an entry for said data item from said single-failure queue without removing the entry for said data item from said multiple-failure queue.

A computer-readable medium carrying instructions for recovering after a failure of one or more nodes of a multiple-node system, the instructions comprising instructions for performing the steps of:

• determining whether the failure involves only one node;
• and
• if the failure involves only said one node, then performing recovery by applying a recovery log of said node beginning at a first point in the recovery log;
• and
• if the failure involves one or more nodes in addition to said one node, then performing recovery by applying said recovery log of said node beginning at a second point in the recovery log;
• wherein said first point is different from said second point.

A computer-readable medium carrying instructions for recovering after a failure of one or more nodes of a multiple-node system, the instructions comprising instructions for performing the steps of:

• if it is unclear whether a particular version of a data item has been written to disk, then performing the steps of without attempting to recover said data item, marking dirtied cached versions of said data item that would have been covered if said particular version was written to disk;
• when a request is made to write one of said dirtied cached versions to disk, determining which version of said data item is already on disk;
• and
• if said particular version of said data item is already on disk, then not writing said one of said dirtied cached versions to disk.

A computer-readable medium carrying instructions for recovering a current version of a data item after a failure of one or more nodes in a system that includes multiple caches, the instructions comprising instructions for performing the steps of:

• modifying the data item in a first node of said multiple caches to create a modified data item;
• sending the modified data item from said first node to a second node of said multiple caches without durably storing the modified data item from said first node to persistent storage;
• after said modified data item has been sent from said first node to said second node and before said data item in said first node has been covered by a write-to-disk operation, discarding said data item in said first node;
• after said failure, reconstructing the current version of said data item by applying changes to the data item on persistent storage based on merged redo logs associated with all of said multiple caches;
• maintaining, for each of said multiple caches, a globally-dirty checkpoint queue and a locally-dirty checkpoint queue;
• wherein the globally-dirty data items associated with entries in the globally-dirty checkpoint queue are not retained until covered by write-to-disk operations;
• determining, for each cache, a checkpoint based on a lower of a first-dirtied time of the entry at the head of the locally-dirty checkpoint queue and the first-dirtied time of the entry at the head of the globally-dirty checkpoint queue;
• and
• after said failure, determining where to begin processing the redo log associated with each cache based on the checkpoint determined for said cache.

A computer-readable medium carrying instructions for recovering a current version of a data item after a failure of one or more nodes in a system that includes multiple caches, the instructions comprising instructions for performing the steps of:

• modifying the data item in a first node of said multiple caches to create a modified data item;
• sending the modified data item from said first node to a second node of said multiple caches without durably storing the modified data item from said first node to persistent storage;
• after said modified data item has been sent from said first node to said second node and before said data item in said first node has been covered by a write-to-disk operation, discarding said data item in said first node;
• after said failure, reconstructing the current version of said data item by applying changes to the data item on persistent storage based on merged redo logs associated with all of said multiple caches;
• maintaining, for each of said multiple caches, a globally-dirty checkpoint queue and a locally-dirty checkpoint queue;
• wherein the globally-dirty data items associated with entries in the globally-dirty checkpoint queue are not retained until covered by write-to-disk operations;
• maintaining, for each cache, a first checkpoint recbrd for the locally-dirty checkpoint queue indicating a first time, where all changes made to data items that are presently dirty in the cache prior to the first time have been recorded on a version of the data item that is on persistent storage;
• maintaining, for each cache, a second checkpoint record for the globally-dirty checkpoint queue, wherein the second checkpoint record includes a list of data items that were once dirtied in the cache but have since been transferred out and not written to persistent storage;
• and
• after said failure, determining where to begin processing the redo log associated with each cache based on the first checkpoint record and said second checkpoint record for said cache.