Thoughts inlined:
On 12/14/15 11:12 AM, Steven Jacobs wrote:
Here are the conclusions that Ildar and I have drawn from looking at the
secondary indexes:
First of all it seems that datasets are local to node groups, but
dataverses can span node groups, which seems a little odd to me.
Node groups are an undocumented but to-be-exploited-someday feature that
allows datasets to be stored on less than all nodes in a given cluster.
As we face bigger clusters, we'll want to open up that possibility. We
will hopefully use them inside w/o having to make users manage them
manually like parallel DB2 did/does. Dataverses are really just a
namespace thing, not a storage thing at all, so they are orthogonal to
(and unrelated to) node groups.
There are three Metadata secondary indexes: GROUPNAME_ON_DATASET_INDEX,
DATATYPENAME_ON_DATASET_INDEX, DATATYPENAME_ON_DATATYPE_INDEX
The first is used in only one case:
When dropping a node group, check if there are any datasets using this node
group. If so, don't allow the drop
BUT, this index has a field called "dataverse" which is not used at all.
This one seems like a waste of space since we do this almost never. (Not
much space, but unnecessary.) If we keep it it should become a proper
index.
The second is used when dropping a datatype. If there is a dataset using
this datatype, don't allow the drop.
Similarly, this index has a "dataverse" which is never used.
You're about to use the dataverse part, right? :-) This index seems
like it will be useful but should be a proper index.
The third index is used to go in two cases, using two different ideas of
"keys"
It seems like this should actually be two different indexes.
I don't think I understood this comment....
This is my understanding so far. It would be good to discuss what the
"correct" version should be.
Steven
On Mon, Dec 14, 2015 at 10:12 AM, Steven Jacobs <[email protected]> wrote:
Hi all,
I'm implementing a change so that datasets can use datatypes from
alternate data verses (previously the type and set had to be from the same
dataverse). Unfortunately this means another change for Dataset Metadata
(which will now store the dataverse for its type).
As such, I had a couple of questions:
1) Should this change be thrown into the release branch, as it is another
Metadata change?
2) In implementing this change, I've been looking at the Metadata
secondary indexes. I had a discussion with Ildar, and it seems the thread
on Metadata secondary indexes being "hacked" has been lost. Is this also
something that should get into the release? Is there anyone currently
looking at it?
Steven
