On 08/28/2012 09:30 AM, Petr Vobornik wrote:
I would like to point out a problem in Web UI related to paging and
suggest a possible solution:

Current implementation of paging in Web UI is not serving it purpose
which should be to do operations faster and be able to find all users.

How current implementation should work:
   1) get all primary keys (pkeys) of certain object type (users, ...)
   2) load first 20 of them
   3) from 1) we know record count so we can choose other page (different
subset of 20)

How it actually works:
   * get up to 2000 keys, with more items a LDAP limit is reached and
result is truncated
   * we don't know how many are there, paging doesn't work as it should

Problem:
Let's say that paging is working (no LDAP limit) and consider this: Our
page size is 20 records. With 400 users it is 20 pages. With 2000 users
(current search limit) it is 200 pages and so on. Personally I wouldn't
like to go through 20 pages. 200 or more pages sounds like a punishment.
There is also a question if we even need to do it. I don't see a benefit
of paging here. For smaller setup an increase of page size may help
admin to see more users on a page more quickly (rolling mouse wheel is
faster than click on next page button).

For large setups, size of the pkey list must also be taken on mind. For
each record there is a pkey and dn (dn is not required but it would need
some hacking in python code to remove it). At the moment the list size
raises drastically because JSON response includes indenting by spaces
and is not compressed (easy to fix, but still there). With 10 000 or
more users this pkey and dn list is pretty big (slow load on slower
networks -vpns). This list is also loaded on each page change
(record-wise, can be improved - cached).

IMO with hundreds or thousands of users the most common use case is
search by login or name or something. Paging is not required this case.
It may be required if the result count is greater than size limit. In
such case an option to temporary increase size limit or enable paging
would be beneficial. Apart from this case, paging should be off. It will
speed up page load because it executes only one request.

Possible solution:
1) I suggest to introduce configuration options for paging. They can be
global (default for all search pages) or individual for pages or Web
UI's users. Per-user configuration can be stored in browser (to not
pollute LDAP with application stuff). Global configuration on server in
config plugin (minor polluting).

Those options should be (per page and global):
   * enable paging
   * page size

Note: when paging is disabled page size is basically --sizelimit option.

2) On search pages we should have controls to enable/disable paging and
to change sizelimit for this particular moment.
3) Compress JSON responses (on httpd level)

This way admin can configure default's for his deployment and user's can
adjust for certain situations.

Btw always including member_xx attributes in find or show commands is
not good for search pages either but that's another topic.

Comments are welcome.

Your possible solution does not address how many results are fetched (unless I misunderstood).

I'm not sure how per-user preferences are handled in browsers, but don't forget we now have session support in the server. Server session data is available for use.

If you don't want to fetch every record to implement paging smartly in conjunction with it's performance issues why not do the query on the server, cache the results in the session, and have the RPC return the total number of results plus a subset of the result. Another RPC could retrieve the next/previous subset of results from the cached result in the session.

I don't think there any need in JSON formatted data for pretty printing with indentation. Is it an accident or oversight we're pretty printing the JSON data in an RPC. For large data sets compression would be a win, but most of our RPC communication is not large. Compression has an overhead. With small data you'll use more cycles compressing and uncompressing than you would sending verbose but small data blobs. Compression should be an RPC option specified by either side of the connection and the receiver should be prepared to conditionally uncompress based on a flag value in the RPC. If you use server session data to support paging you may not need to introduce compression since you would only be passing one page of data at a time.

User specified page size (without limitation) is an absolute necessity. I am frequently annoyed by web sites which either do not allow me to specify page size or constrain it to ridiculous hard coded limits such as 10, 20 or 30.


--
John Dennis <jden...@redhat.com>

Looking to carve out IT costs?
www.redhat.com/carveoutcosts/

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