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For example if I have 5 servers (A, B, C, D, E)

Can we set the data distributed with replication factor of 3? (for example one write goes to ABC, other records goes to ABD, other record goes to ABE, and so on), so when node C had some hardware failure, there still some record exists.

Can we also add a new node then balance the stored data to the new node without downtime?

Kokizzu
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1 Answers1

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Yes, it can do that, but not in the way you are thinking. What you are describing would be NoSQL setup. Postgres-XL is an MPP database.

When you create a table you define it's "DISTRIBUTED BY" option which can be replication, round robin, hash, modulo, etc. You will need to review the details of each option. You can also define table spaces to be on defined nodes.

Your setup would be something like

  • Node1 Transaction Manger
  • Node2 Transaction Manger Proxy
  • Node3 Coordinator1 & Data Node1
  • Node4 Coordinator2 & Data Node2
  • Node5 Data Node3

NOTE: Important to point out that as I just discovered Postgres-XL has no HA or fail over support. Meaning that if a single node failed the database is down and will require manual intervention. Worse if you are using the round robin, hash, modulo sharing options if you lose the disk on a single node you have lost your database entirely.

You can have stand by nodes that mirror each of your nodes, but this will double the number of nodes you need and it will still not fail over. You will have to manually configure it to use the standby node and restart it.

BrianC
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  • What if you used keepalived and mirrored each data node? – Greg0ry Apr 18 '17 at 03:36
  • Yes, as I mentioned you can mirror setup a mirror of each node. That literally doubles the number of servers you need and the costs, and the management headache. I do not think keepalive will work since at least from what I read all the mirrored nodes are in read-only config for performance reasons. Also that would be a second load balancing step for each node INSIDE a clustered setup which would likely slow things down a lot, and add a LOT of new failure points. – BrianC Apr 18 '17 at 16:11
  • Bottom line the official docs say if a node fails you have to manually take the DB down removed the failed node from the config, and add the mirrored node, and then reboot. You can try to rig a way around it, but it will not be supported, and would likely still fail from unforeseen issues. If you need HA and fail over this is no the option you want to go with. – BrianC Apr 18 '17 at 16:12
  • Thanks @BrianC, you are active on the subject of Postgres-XL, can you help with this problem? http://stackoverflow.com/questions/43620071/bind-postgres-xl-coordinator-to-listen-only-on-speciffic-interface – Greg0ry Apr 25 '17 at 20:10
  • Sorry, no we dumped Postgres-XL when we learned it can not support failover. – BrianC Apr 25 '17 at 21:10