On 09/10/2013 01:47 AM, Ludwig Krispenz wrote:
On 09/09/2013 07:19 PM, Rich Megginson wrote:
On 09/09/2013 02:27 AM, Ludwig Krispenz wrote:
On 09/07/2013 05:02 AM, David Boreham wrote:
On 9/6/2013 8:49 PM, Nathan Kinder wrote:
This is a good idea, and it is something that we discussed briefly
off-list. The only downside is that we need to change the index
format to keep a count of ids for each key. Implementing this
isn't a big problem, but it does mean that the existing indexes
need to be updated to populate the count based off of the contents
(as you mention above).
I don't think you need to do this (I certainly wasn't advocating
doing so). The "statistics" state is much the same as that proposed
in Rich's design. In fact you could probably just use that same
information. My idea is more about where and how you use the
information. All you need is something associated with each index
that says "not much point looking here if you're after something
specific, move along, look somewhere else instead". This is much
the same information as "don't use a high scan limit here".
In the short term, we are looking for a way to be able to improve
performance for specific search filters that are not possible to
modify on the client side (for whatever reason) while leaving the
index file format exactly as it is. I still feel that there is
potentially great value in keeping a count of ids per key so we
can optimize things on the server side automatically without the
need for complex index configuration on the administrator's part.
I think we should consider this for an additional future enhancement.
I'm saying the same thing. Keeping a cardinality count per key is
way more than I'm proposing, and I'm not sure how useful that would
be anyway, unless you want to do OLAP in the DS ;)
we have the cardinality of the key in old-idl and this makes some
searches where parts of the filter are allids fast.
I'm late in the discussion, but I think Rich's proposal is very
promising to address all the problems related to allids in new-idl.
We could then eventually rework filter ordering based on these
configurations. Right now we only have a filter ordering based on
index type and try to postpone "<=" or similar filter as they are
known to be costly, but this could be more elaborate.
An alternative would be to have some kind of index lookup caching.
In the example in ticket 47474 the filter is
(&(|(objectClass=organizationalPerson)(objectClass=inetOrgPerson)(objectClass=organization)(objectClass=organizationalUnit)(objectClass=groupOf
Names)(objectClass=groupOfUniqueNames)(objectClass=group))(c3sUserID=EndUser0000078458))"
and probably only the "c3sUserID=xxxxx" part will change, if we
cache the result for the (&(|(objectClass=... part, even if it is
expensive, it would be done only once.
Thanks everyone for the comments. I have added Noriko's suggestion:
http://port389.org/wiki/Design/Fine_Grained_ID_List_Size
David, Ludwig: Does the current design address your concerns, and/or
provide the necessary first step for further refinements?
yes, the topic of filter reordering or caching could be looked at
independently.
Just one concern abou the syntax:
nsIndexIDListScanLimit:
maxsize[:indextype][:flag[,flag...]][:value[,value...]]
since everything is optional, how do you decide if in
nsIndexIDListScanLimit: 6:eq:AND "AND" is a value or a flag ?
and as it defines limits for specific keys, could the attributname
reflect this, eg nsIndexKeyIDListScanLimit or nsIndexKeyScanLimit or
... ?
Thanks, yes, it is ambiguous.
I think it may have to use keyword=value, so something like this:
nsIndexIDListScanLimit: limit=NNN [type=eq[,sub]] [flags=ADD[,OR]]
[values=val[,val...]]
That should be easy to parse for both humans and machines.
For values, will have to figure out a way to have escapes (e.g. if a
value contains a comma or an escape character). Was thinking of using
LDAP escapes (e.g. \, or \032)
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