Paper Summary: A Taxonomy Of Partitioned Replicated Cloud-Based Database Systems
This newspaper is past times Divy Agrawal, Amr El Abbadi, too Kenneth Salem, too appeared inward IEEE Data Engineering mag inward 2015.
This newspaper proposes a taxonomy of large scale partitioned replicated transactional databases. Partitioned replicated means, the database is divided inward partitions too the partitions are replicated across dissimilar sites equally inward Figure 1. The motivation for partitioning is scalability, too the motivation for replication is to enable high availability fifty-fifty when closed to of the replicas are down. For geo-replicated databases, sites are maintained at dissimilar datacenters/regions, although the newspaper surveys non-geo-replicated databases equally well.
Figure 2 shows the proposed taxonomy. Replicated object systems is a unmarried leaf. Replicated transactions systems farther split inward to symmetric too asymmetric replicated systems.
If y'all similar to refresh your noesis of these systems, here is a link to my Spanner review, too here a link to my Granola review.
A tablet inward Spanner is a collection of directories or fragments of directories. Tablets represent to partitions of the database too they are replicated across sites. Spanner uses Paxos to synchronize the replicas of each division across sites. Spanner uses a separate instance of Paxos, amongst a long-lived leader, for each partition.
To implement transactions (including multiple division transactions) Spanner uses two-phase locking for concurrency control, too two-phase commit. The Paxos leader inward each division is responsible for participating inward these protocols on behalf of that partition. It does hence inward much the same way that it would if its division were non replicated, except that changes to the partition's terra firma are replicated using Paxos instead of only existence stored locally at the leader's server. The leaders serve equally the link betwixt the transaction protocols too Paxos past times ensuring that both database updates too changes inward the terra firma of the transaction are replicated.
Each site has a local transaction manager that ensures that its local transactions convey ACID properties amongst honour to other local transactions at that site. Each local transaction is responsible for applying the effects of its rear global transaction to the replicas at its ain local site.
In symmetric replicated transaction systems, all of the local transactions of a given rear transaction are the same too run concurrently at the dissimilar sites. In the UCSB's replicated commit protocol the global transaction volition endure committed if the local coordinators at a bulk of the sites vote to commit it. In render a customer that wishes to read information from a division sends its read asking to all replicas of that partition, waits for a bulk of the replicas to respond, too chooses the latest version that it receives from that majority. (Similar to the thought inward Attiya, Bar-Noy, too Dolev, 1995.)
In an asymmetric replicated system, ane local original transaction runs commencement at a unmarried site. If that local transaction is able to commit, hence the remaining local transactions are run at the other sites. These remaining transactions are called update propagation transactions. Typically, the update propagation transactions perform solely the updates of the original transaction, too create non perform whatever reads.
An instance of an asymmetric replicated primary re-create system is Microsoft's Cloud SQL Server, which is the database administration organisation behind the SQL Azure cloud relational database service. Cloud SQL server is non designed for geo-replication, hence all of database replicas ("sites") are located inward the same datacenter. Transactions are express to a unmarried partition unless they are willing to run at the read committed SQL isolation level.
An instance of an asymmetric replicated update anywhere system is Google Megastore, where database partitions (called entity groups) are replicated too geographically distributed. In Megastore, a customer tin forcefulness out initiate a single-partition transaction at whatever replica of that division --typically, the customer volition move a nearby replica. For each partition, Megastore manages a transaction log, which is replicated to all sites using Paxos to ensure that transactions commit inward the same club everywhere. Here is a link to my Megastore review.
I gauge Yahoo PNUTS could endure considered somewhere betwixt primary re-create too update anywhere organisation due to its per-record original scheme.
This newspaper proposes a taxonomy of large scale partitioned replicated transactional databases. Partitioned replicated means, the database is divided inward partitions too the partitions are replicated across dissimilar sites equally inward Figure 1. The motivation for partitioning is scalability, too the motivation for replication is to enable high availability fifty-fifty when closed to of the replicas are down. For geo-replicated databases, sites are maintained at dissimilar datacenters/regions, although the newspaper surveys non-geo-replicated databases equally well.
The taxonomy
The taxonomy is based on the human relationship betwixt transaction administration too replica management. This newspaper considers transactions that furnish one-copy serializability guarantee, where concurrent transactions comport equally if they execute sequentially on a unmarried database. For a partitioned database, it is necessary to coordinate the database partitions to enforce transactional (ACID) guarantees. In addition, inward club to back upwards replication, the database organisation must too synchronize the database replicas hence that replication tin forcefulness out endure hidden from the application.Replicated object systems
Replicated object systems implement transaction administration on move past times of replica management, which ensures that partitions are consistently replicated across sites. A prominent instance of this category is Spanner, closed to other is Granola (which is non geo-replicated).If y'all similar to refresh your noesis of these systems, here is a link to my Spanner review, too here a link to my Granola review.
A tablet inward Spanner is a collection of directories or fragments of directories. Tablets represent to partitions of the database too they are replicated across sites. Spanner uses Paxos to synchronize the replicas of each division across sites. Spanner uses a separate instance of Paxos, amongst a long-lived leader, for each partition.
To implement transactions (including multiple division transactions) Spanner uses two-phase locking for concurrency control, too two-phase commit. The Paxos leader inward each division is responsible for participating inward these protocols on behalf of that partition. It does hence inward much the same way that it would if its division were non replicated, except that changes to the partition's terra firma are replicated using Paxos instead of only existence stored locally at the leader's server. The leaders serve equally the link betwixt the transaction protocols too Paxos past times ensuring that both database updates too changes inward the terra firma of the transaction are replicated.
Replicated transaction systems
Replicated transaction systems implement replica administration on move past times of transaction management. Transactions run over private division replicas, rather than ane logical division equally was the instance inward replicated object systems.Each site has a local transaction manager that ensures that its local transactions convey ACID properties amongst honour to other local transactions at that site. Each local transaction is responsible for applying the effects of its rear global transaction to the replicas at its ain local site.
In symmetric replicated transaction systems, all of the local transactions of a given rear transaction are the same too run concurrently at the dissimilar sites. In the UCSB's replicated commit protocol the global transaction volition endure committed if the local coordinators at a bulk of the sites vote to commit it. In render a customer that wishes to read information from a division sends its read asking to all replicas of that partition, waits for a bulk of the replicas to respond, too chooses the latest version that it receives from that majority. (Similar to the thought inward Attiya, Bar-Noy, too Dolev, 1995.)
In an asymmetric replicated system, ane local original transaction runs commencement at a unmarried site. If that local transaction is able to commit, hence the remaining local transactions are run at the other sites. These remaining transactions are called update propagation transactions. Typically, the update propagation transactions perform solely the updates of the original transaction, too create non perform whatever reads.
An instance of an asymmetric replicated primary re-create system is Microsoft's Cloud SQL Server, which is the database administration organisation behind the SQL Azure cloud relational database service. Cloud SQL server is non designed for geo-replication, hence all of database replicas ("sites") are located inward the same datacenter. Transactions are express to a unmarried partition unless they are willing to run at the read committed SQL isolation level.
An instance of an asymmetric replicated update anywhere system is Google Megastore, where database partitions (called entity groups) are replicated too geographically distributed. In Megastore, a customer tin forcefulness out initiate a single-partition transaction at whatever replica of that division --typically, the customer volition move a nearby replica. For each partition, Megastore manages a transaction log, which is replicated to all sites using Paxos to ensure that transactions commit inward the same club everywhere. Here is a link to my Megastore review.
I gauge Yahoo PNUTS could endure considered somewhere betwixt primary re-create too update anywhere organisation due to its per-record original scheme.
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