DecentSched

This repository contains the implementation of DecentSched as a ready-to-use user-level library. The detailed design is introduced in our paper, "Fast Abort-Freedom for Deterministic Transactions" on IPDPS '24.

[Paper PDF]

DecentSched is a concurrency control protocol for deterministic transactions (i.e., transactions with known read/write key set before execution). It utilizes queue-based ordering and decentralized scheduling to let transactions execute efficiently. It provides serializable isolation between concurrent transactions.

In the implementation, qcc is the name of the protocol across all repositories.

Example

In the repository, test_qcc.c demonstrates the basic usage of DecentSched. To compile it, the repository already contains a Makefile so you can just run make to compile it.

The compiled test_qcc.out program simulates a single-table database where each row is a number. It spawns multiple worker threads. Each thread randomly reads or writes multiple numbers and all accesses are wrapped in a transaction. The thread will execute multiple such transactions, and finally the results are validated against the correct ones.

The program accepts two arguments:

./test_qcc.out <nr_workers> <nr_rows>

where nr_workers specifies the total number of threads and nr_rows is the total number of rows (numbers) in the data store.

The test program also supports a TEST_ENHANCED_CONCURRENCY flag, which enables opportunistic execution of transactions. It can be set to test its functionality.

API

For complete API and function signatures, you can refer to qcc.h file. Here we document the usage of core functions in the library.

Function	Usage
qcc_create	Create a struct qcc which records all the metadata of the concurrency control. The struct is useful for core function calls.
qcc_ready	Called by a worker thread to synchronize after all thread-local preparation works are done.
qcc_acquire	Called by a worker thread to acquire a new empty transaction.
qcc_txn_enqueue	Called by a worker thread to enqueue the queuing entries for all accesses.
qcc_txn_wait	Blocking the worker thread until its current transaction can execute according to the global schedule.
qcc_txn_finish	Marking the current transaction as finished after execution (commit).
qcc_sync	Synchronizing all worker threads on a global barrier. Used interally for epoch-based memory management.
qcc_snapshot_*	Taking a version number snapshot of all accessed items (for opportunistic execution).