Ramblings On Serializability
Here is a really raw/immature sentiment I convey been toying alongside recently. I decided to write it downwardly together with percentage inwards companionship to acquire feedback most whether this is worth exploring further.
While serialization is non an halt inwards Paxos but rather a means, Paxos is seen show equally a defacto method for serialization rather than a method for fault-tolerant soil automobile replication. Maybe the ZooKeeper implementation of a Paxos-based lock-service assist promote this confusion together with blur the lines betwixt Paxos's truthful destination (fault-tolerant replication) alongside its side termination (serialization).
In fact Paxos serialization is overkill, it is also strong. Paxos volition serialize operations inwards a full order, which is non necessarily needed for sequential consistency. Today inwards many applications where knowing the full companionship together with replicated-logging of that companionship is non important, Paxos is all the same (ab)used.
Serialization is non together with should non travel tightly-related to a replication solution.
(Probably at that spot are other problems that arise due to this confusion, but for right away I am exclusively picking on this one.)
By adopting the proactive serialization philosophy, a lock service tin furnish the locks to only about workers proactively thus those workers tin acquire ahead. Embracing this philosophy, a lock-servicemaster tin anticipate a time to come asking together with furnish only about locks ahead of time. The create goodness of this is to eliminate the demand for an explicit asking (again inwards a fraction of the cases) together with improve throughput together with trim latency.
A couplet paragraphs to a higher house I said that "Today inwards many applications where knowing the full companionship together with replicated-logging of that companionship is non important, Paxos is all the same (ab)used." Picking upward on that thread I volition claim farther (without much evidence for now) that inwards those cases, proactive serialization could create a ameliorate job.
Employing presignaling tin travel only about other approach to make proactive serialization. The nodes tin anticipate which locks they volition travel needing inwards the side past times side circular or infinitesimal together with inquire for those locks inwards volume speculatively. The lock service tin select to award only about of these requests together with make proactive serialization to improve performance.
Another approach to make proactive serialization tin travel to create a static analysis of workers' programs/actions together with come upward up alongside patterns/sequence of accesses. When the lock service observes ane of the detected patterns, it tin orbit the locks inwards advance to the respective workers that are mentioned inwards the residue of the pattern.
However, Paxos serialization inwards full companionship is all the same overkill together with tin drive problems inwards a Paxos-based solution. Google Spanner used a smart solution of assigning assort conflict domains (at the tablet level) to Paxos groups. This mode it was able to furnish locks inwards parallel across assort conflict domains.
If nosotros create non tightly-couple serialization alongside a Paxos-based replication service, nosotros tin divulge to a greater extent than efficient together with novel solutions for serialization.
Serializability
Serializability of reads together with writes (sequential consistency) is an of import characteristic inwards distributed systems. A pregnant application of serializability is inwards transaction processing inwards distributed databases (e.g., Spanner).Paxos serialization versus serializability
Paxos is a method for fault-tolerant soil automobile replication. In companionship to make fault-tolerant soil automobile replication, Paxos employs consensus to serialize operations at a leader together with apply the operations at each replica inwards this exact serialized companionship (dictated past times the leader).While serialization is non an halt inwards Paxos but rather a means, Paxos is seen show equally a defacto method for serialization rather than a method for fault-tolerant soil automobile replication. Maybe the ZooKeeper implementation of a Paxos-based lock-service assist promote this confusion together with blur the lines betwixt Paxos's truthful destination (fault-tolerant replication) alongside its side termination (serialization).
In fact Paxos serialization is overkill, it is also strong. Paxos volition serialize operations inwards a full order, which is non necessarily needed for sequential consistency. Today inwards many applications where knowing the full companionship together with replicated-logging of that companionship is non important, Paxos is all the same (ab)used.
Serialization is non together with should non travel tightly-related to a replication solution.
OK, thus what? (What is incorrect alongside using a drug for its side effect?)
This confusion may permeate the misconception that serialization is inherently a reactive process. Many people convey right away been thinking most serialization from the Paxos perspective together with equally an inherently on-demand process.(Probably at that spot are other problems that arise due to this confusion, but for right away I am exclusively picking on this one.)
Proactive serialization
Serialization tin genuinely travel proactive together with anticipatory. The workers does non demand to brand a serialization asking to a Paxos leader. By getting rid of such a asking (albeit inwards a fraction of the cases), latency tin travel reduced together with throughput tin travel improved.By adopting the proactive serialization philosophy, a lock service tin furnish the locks to only about workers proactively thus those workers tin acquire ahead. Embracing this philosophy, a lock-service
A couplet paragraphs to a higher house I said that "Today inwards many applications where knowing the full companionship together with replicated-logging of that companionship is non important, Paxos is all the same (ab)used." Picking upward on that thread I volition claim farther (without much evidence for now) that inwards those cases, proactive serialization could create a ameliorate job.
What are only about ways to make proactive serialization?
How tin proactive serialization travel achieved? One approach is to employ automobile learning. The lock service learns the patterns of requests for locks over fourth dimension together with and then starts distributing these locks speculatively earlier they are requested.Employing presignaling tin travel only about other approach to make proactive serialization. The nodes tin anticipate which locks they volition travel needing inwards the side past times side circular or infinitesimal together with inquire for those locks inwards volume speculatively. The lock service tin select to award only about of these requests together with make proactive serialization to improve performance.
Another approach to make proactive serialization tin travel to create a static analysis of workers' programs/actions together with come upward up alongside patterns/sequence of accesses. When the lock service observes ane of the detected patterns, it tin orbit the locks inwards advance to the respective workers that are mentioned inwards the residue of the pattern.
Did I alternative on Paxos unfairly?
Actually, none of these proactive approaches are ruled out inwards Paxos. The Paxos leader itself could travel making these proactive/speculative lock giving requests inwards advance. So, did I genuinely demand to alternative on Paxos? Maybe not.However, Paxos serialization inwards full companionship is all the same overkill together with tin drive problems inwards a Paxos-based solution. Google Spanner used a smart solution of assigning assort conflict domains (at the tablet level) to Paxos groups. This mode it was able to furnish locks inwards parallel across assort conflict domains.
If nosotros create non tightly-couple serialization alongside a Paxos-based replication service, nosotros tin divulge to a greater extent than efficient together with novel solutions for serialization.
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