> So, the issue is that you have multiple items with the same > key. This is simply handled by using sets as values ion a BTree. > There are existing index implementations that do this. > > Hmm... no, in fact the problem is that most of the time I will have only one value per index entry.So, in a relational DB i would do something like: >> SELECT * FROM table WHERE timestamp>= X AND timestamp<= Y >> >> Since I cannot do this with ZODB, >> > I don't know what "this" is. Range seaches? SQL? BTrees and various > index implementations based on the,m support range searches. of > course, ZODB doesn't support SQL. >
Yes, I know ZODB doesn't support SQL, I was just trying to demonstrate my use case. What I meant was that in relational DBs a query like the one above can be performed over an arbitrary table, without the need for having an extra data structure for indexing. >> I'd have to have a BTree, indexed by >> timestamp... however, as you said, if I want "to the second" granularity, I >> will rarely have two items with the same key (which makes it pretty >> useless). >> > I don't know why it is useless, but it is easily handled. > > It's not useless. I'm sorry, I have used the wrong word. I meant that a range query will normally involve the union of a higher number of sets as the granularity gets smaller and smaller. If there is only one item per index entry, the union operation will take longer... I assumed that the more BTree entries we have, the more buckets we will have to fetch from the DB, for a given range query. But I am probably wrong... >> So, I was wondering if there is some data structure I can use for this, as >> this seems to be a pretty common use case. >> > That's why the various indexing(/catalog) schemes already support it. > So, if I need an index where items can be queried by date, and range queries can be performed efficiently, an IOBTree will do the job? As I mention above, my only concern is the number of sets that will have to be joined. Thanks, once again, Pedro -- José Pedro Ferreira Indico Team IT-UDS-AVC 513-R-0042 CERN, Geneva, Switzerland _______________________________________________ For more information about ZODB, see the ZODB Wiki: http://www.zope.org/Wikis/ZODB/ ZODB-Dev mailing list - ZODB-Dev@zope.org https://mail.zope.org/mailman/listinfo/zodb-dev
