High-throughput algorithm for multiversion concurrency control with globally synchronized time
Throughput is preserved in a distributed system while maintaining concurrency by pushing a commit wait period to client commit paths and to future readers. As opposed to servers performing commit waits, the servers assign timestamps, which are used to ensure that causality is preserved. When a server executes a transaction that writes data to a distributed database, the server acquires a user-level lock, and assigns the transaction a timestamp equal to a current time plus an interval corresponding to bounds of uncertainty of clocks in the distributed system. After assigning the timestamp, the server releases the user-level lock. Any client devices, before performing a read of the written data, must wait until the assigned timestamp is in the past.
1. A system, comprising:
a server device, the server device including at least one input/output to communicate with other servers and clients in a distributed computing environment, the server device comprising:
one or more processors configured to:
receive a request to write first data;
write the first data to a memory in the distributed computing environment;
while the first data is being committed to the memory, the effects of the first data are not visible to at least one of a client library, the other servers, or the clients for an interval of time, without preventing writing of second data to the memory during the interval of time.
2. The system of claim 1 , wherein the interval of time is imposed on the clients, and wherein the one or more processors are further configured to:
assign a timestamp to the first data, the timestamp equal to a first time plus the interval; and
release a lock after assigning the timestamp.
3. The system of claim 2 , wherein the first time is a current time reflected by a local clock at the server when the server assigns the timestamp to the first data.
4. The system of claim 3 , wherein the interval corresponds to a difference in time between a latest time reported by all clocks in the distributed system and an earliest time reported by all clocks in the distributed system.
5. The system of claim 4 , wherein the interval is maintained by the local clock at the server.
6. The system of claim 2 , wherein any of the clients, before reading the first data, must wait until the assigned timestamp is in the past.
7. The system of claim 6 , wherein the assigned timestamp is in the past when a local clock at the client reading the first data reflects a current time that is later than the assigned timestamp.
8. The system of claim 1 , wherein the effects of the first data are not visible to both the client library and the other servers during the interval of time.
9. The system of claim 8 , wherein the client library notifies one of the clients after the interval of time that the first data was committed.
10. The system of claim 8 , wherein the other servers execute a transactional read during the interval of time.
11. A method, comprising:
receiving, at a first computing device, a request from one or more clients to write first data to a distributed computing environment;
obtaining, at the first computing device, a write lock; and
writing, by the first computing device, the first data to a memory in the distributed computing environment;
wherein while the first data is being committed to the memory, the effects of the first data are not visible to at least one of a client library, other servers, or clients for an interval of time, without preventing writing of second data to the memory during the interval of time.
12. The method of claim 11 , wherein the interval of time is imposed on the clients, and further comprising:
assigning a timestamp to the first data, the timestamp equal to a first time plus the interval;
releasing a lock after assigning the timestamp.
13. The method of claim 12 , wherein any of the clients, before reading the data, must wait until the assigned timestamp is in the past.
14. The method of claim 13 , wherein the assigned timestamp is in the past when a local clock at the client reading the data reflects a current time that is later than the assigned timestamp.
15. The method of claim 12 , wherein the first time is a current time reflected by a local clock at the server when the server assigns the timestamp to the first data, and wherein the interval corresponds to a difference in time between a latest time reported by all clocks in the distributed system and an earliest time reported by all clocks in the distributed system.
16. The method of claim 11 , wherein the effects of the first data are not visible to both the client library and the other servers during the interval of time.
17. The method of claim 16 , wherein the client library notifies one of the clients after the interval of time that the first data was committed.
18. The method of claim 16 , wherein the other servers execute a transactional read during the interval of time.