Oracle International Corporation

Achin Mishra

Virendra J Marathe

Margo I Seltzer

Steve Byan

Amee Trivedi

Systems implementing copy-on-write (COW) as described herein may reduce the number of persist barriers executed within a transaction. For instance, a system may eliminate some, most or all persist barriers related to memory allocation/deallocation in COW transactions. A COW implementation may introduce an extra level of indirection between a persistent type instance and the real data type it encloses. A persistent type may include pointers to old and new versions of the enclosed type's instances. Before modifying an object, a transaction may modify a copy-on-write persistent object and create a new copy of the payload. The modified object may be added to a list of objects written to by the transaction. The transaction may be committed by issuing persist barriers in the commit operation.

Committing copy-on-write transaction with a persist barrier for a persistent object including payload references

Applications may allocate and deallocate persistent objects within transactions used to access persistent data. An allocator's persistent metadata may be lazily persisted when the enclosing transaction commits. An allocator's metadata may be divided into persistent and nonpersistent portions while the heap may be divided into shared and thread-private superblocks. The persisting of the effects of allocation/deallocation calls may be lazily performed and bundled with the enclosing transaction's commit operation related persist barriers. A transaction may maintain an allocation log of the allocation/deallocation calls made by the transaction. An allocation log may be hosted in persistent memory and updated during allocation/deallocation calls. No persist barriers may be used during allocation/deallocation calls. Before a transaction commits, its updates and allocation log may be persisted. Once the transaction has been committed, the allocation log may be applied to the heap's corresponding metadata.

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Achin Mishra