database dual-system hot standby has two typical ways, one is more standard, two servers through a shared storage device (usually a shared disk array Or storage area network (SAN), and install dual-machine software to achieve dual-system hot standby, called sharing mode. Another way is through pure software, generally called pure software or mirroring.
For sharing, the database is placed on a shared storage device. When a server provides services, it reads and writes directly on the storage device. When the system is switched, another server also reads the data on the storage device.
In the pure software way, the data can be copied to another server in real time through the mirroring software, so that the same data exists on each of the two servers. If one server fails, You can switch to another server in time.
Pure software can reduce costs to a certain extent, but it also has very obvious shortcomings:
1. Reliability is relatively poor, real-time data replication between two servers is a relatively fragile Link.
2. Once a server is interrupted, more complex data synchronization recovery is required after recovery. Also, the system is unprotected during this time period.
3. There is no transaction mechanism. Since the replication is performed at the file and disk level, whether the replication succeeds does not affect the database transaction operation, so there is a situation in which the data is incompletely changed. This has considerable risks. .
Therefore, it is recommended that you do not choose a pure software solution unless you have to.
But on the other hand, there is a database parallel solution, which does not copy at the file or disk level, but directly distributes the database operations on the front end, and completes the database update in parallel with the transaction mechanism. At the same time, it can also provide parallel services for the database. This method is currently very successful for SQL SERVER applications, significantly better than shared storage + dual-machine software
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