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From Joan Touzet <woh...@apache.org>
Subject Re: _global_changes purpose
Date Tue, 27 Jun 2017 06:12:18 GMT
I'll update the docs. However, for now we have:

---
When a database is created, deleted, or updated, a corresponding event will be persisted to
disk (Note: This was designed without the guarantee that a DB event will be persisted or ever
occur in the _db_updates feed. It probably will, but it isn't guaranteed). Users can subscribe
to a _changes-like feed of these database events by querying the _db_updates endpoint.

When an admin user queries the /_db_updates endpoint, they will see the account name associated
with the DB update as well as update
---
And technically, the endpoint can work without the _global_changes database, but be aware:

---
3: global_changes, update_db: (true/false) A flag setting whether to update the global_changes
database. If false, changes will be lost and there will be no performance impact of global_changes
on the cluster.
---

This is all from https://github.com/apache/couchdb-global-changes

I also learned something new today!

-Joan

----- Original Message -----
From: "Vladimir Kuznetsov" <vovanec@gmail.com>
To: "Joan Touzet" <wohali@apache.org>
Cc: user@couchdb.apache.org
Sent: Tuesday, 27 June, 2017 1:53:02 AM
Subject: Re: _global_changes purpose

Thanks Joan. 

Very good to know. It'd be great to have this reflected somewhere in the official couchdb
2.0 docs. Probably it is already there I just could not find that...

thanks,
--Vovan

> On Jun 26, 2017, at 10:42 PM, Joan Touzet <wohali@apache.org> wrote:
> 
> _db_updates is powered by the _global_changes database.
> 
> -Joan
> 
> ----- Original Message -----
> From: "Vladimir Kuznetsov" <vovanec@gmail.com>
> To: user@couchdb.apache.org, "Joan Touzet" <wohali@apache.org>
> Sent: Tuesday, 27 June, 2017 12:39:55 AM
> Subject: Re: _global_changes purpose
> 
> Hi Joan
> 
> I heard /_db_updates is the feed-like thing I could subscribe to listen to the global
updates(same way you described). It is not very clear why would I need access to _global_changes
database when I already have /_db_updates method with pagination and long-polling features.
> 
> Is listening on _global_changes's /_changes feed the same as listening on /_db_updates?
Or is there any difference? What is preferred?
> 
> thanks,
> --Vovan
> 
> 
>> On Jun 26, 2017, at 9:21 PM, Joan Touzet <wohali@apache.org> wrote:
>> 
>> Say you have 100 databases and you want to know when something changes on all
>> of them. In 1.x you have to open 100 _changes continuous feeds to get that
>> information. In 2.x you have to open a single connection to _global_changes.
>> 
>> Think of the possibilities.
>> 
>> -Joan
>> 
>> ----- Original Message -----
>> From: "Vladimir Kuznetsov" <vovanec@gmail.com>
>> To: user@couchdb.apache.org
>> Sent: Monday, 26 June, 2017 8:47:46 PM
>> Subject: _global_changes purpose
>> 
>> Hi guys
>> 
>> I cannot find any good explanation what's the purpose of _global_changes system database
in CouchDB 2.0. Can somebody please explain or provide some pointer?
>> 
>> thanks
>> --Vovan
> 

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