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Replication Process

Log Files

In SequoiaDB, it with log for data synchronization among data nodes, the log files is in the directory replicalog. The size and number of log file can be configured by setting 20. It can't be modified if the params has entryed into force. (if you want to modify, you must delete all the log files off-line, reconfigure the params and restart SequoiaDB. But this will lead to full-sync.)

Sync

All slave nodes in data group will regularly packaged download the logs of other nodes to local for log replaying. Sync source is not limited to the master node. As we are hope the gap of data version in all nodes is in the range of a small window. When in the range of window, all the slave nodes synchronize to master node. But when the data version of some nodes is too larger differ from master node, they will select other slave nodes to synchronize. And if have conficted versions, be based on the current data verson of master node. If the confiction can't be solved, then enter into full-sync.No master node, no sync.

Full-sync

Causes of triggering full-sync:

1. downtime and restart.

2. data version of some nodes is too large differ from other nodes.

3. the data is inconsistent and can't be repaired.

Note: After restarting in mormal, If the data version is still in the range of synchronization, then it will not trigger full-sync.

the node which experienced full-sync will clear all of local data and logs, and copy all of data in another node(not limit master node) in the group to local, as well as the changed data in sync source. The node in the time of full-sync does not provide services to external, and no master node, no sync. Full-sync will greatly affect the performance of data group, and even lead to lower the synchronous performance of other slave nodes. So adding shardings or increating log size to avoid full-sync for proposing.

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SequoiaDB is a financial-level distributed database vendor and is the first Chinese database listed in Gartner’s Magic Quadrant OPDBMS report. SequoiaDB has recently released version 3.0.
SequoiaDB is now penetrating the vertical sector Financial Industry quickly and had more than 50 banking clients and hundreds of enterprise customers in industries including government, telecommunication, Internet and IoT.

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