[postgres-xl-bugs] about logical replication
irene7788
irene7788 at 163.com
Wed Oct 11 23:35:06 PDT 2017
> 在 2017年10月12日,上午3:35,Tomas Vondra <tomas.vondra at 2ndquadrant.com> 写道:
>
>
>
> On 10/11/2017 07:53 AM, Pavan Deolasee wrote:
>>
>>
>> On Wed, Oct 11, 2017 at 6:58 AM, irene7788 <irene7788 at 163.com
>> <mailto:irene7788 at 163.com>> wrote:
>>
>> I’m sorry, I didn't make the things clear. So, I describe it again.
>>
>> 1、my test environment
>> one gtm
>> one slave gtm
>> two data node( with two coordinator node )
>> two slave datanode ( with two slave coordinator node ) — by
>> hot-standby repicas
>>
>>
>> 2、my requirement
>>
>> I can read and write on main node, and the slave nodes can be
>> read online.
>>
>
> I don't follow. Who will read directly from the logical replicas? The
> subset of data replicated to each datanode is somewhat unpredictable, so
> I don't see how this could work in practice. Can you elaborate?
Transaction access master node. The slave node is not a subset, it’s a full copy.
The slave node has two uses,the one is backup,and the other is for online query.
So, we need an efficient method to replicate.
>
>> 3、problems
>> I can connect coordinator node and data node use psql.
>> But I can’t connect any slave coordinator node or slave data node
>> use psql. The error message is "Was unable to obtain a snapshot
>> from GTM.”
>>
>>
>> Unfortunately, that functionality is currently not available. But it
>> should be coming in Postgres-XL 10 (not yet committed to the code though).
>>
>>
>>
>> Another question,Could I use logical replication in postgres-xl ?
>>
>>
>> You can use XL as a subscriber to a PG provider. This can help you
>> consolidate data from multiple providers into a single XL cluster for
>> data analytics. While in theory, it should be possible to use XL
>> datanode as a provider, we haven't tested that configuration and hence
>> most likely not work off the shelf.
>>
>
I need a cluster database, store data distribution in different database in a cluster.
Not to collect multiple databases to one PG.
> Also, it will only have a subset of the data (depending on what
> distribution strategy is defined for the tables). And if there are
> replicated tables, the streams from datanodes will overlap.
In pg-xl,different nodes,I will store different data. So each the slave node is same with main node.
Could this avoid oerlap?
>
> You might setup logical replication for all datanodes, but I'm not sure
> how we could decode distributed transactions in a reasonable way? I'm
> not an expert in logical replication, though.
If I don't use logical replication, how could I can make the slave node readable?
>
>
> regards
>
> --
> Tomas Vondra http://www.2ndQuadrant.com
> PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
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