"What scatter/gather? " http://www.slideshare.net/doanduyhai/sasi-cassandra-on-the-full-text-search-ride-voxxed-daybelgrade-2016/23
"If you partition your data by user_id then you query only 1 shard to get sorted by time visitors for a user" Exact, but in this case, you're using a 2nd index only for sorting right ? For SASI it's not even possible. Maybe it can work with Statrio Lucene impl On Tue, Oct 4, 2016 at 2:15 PM, Dorian Hoxha <dorian.ho...@gmail.com> wrote: > @DuyHai > > What scatter/gather? If you partition your data by user_id then you query > only 1 shard to get sorted by time visitors for a user. > > On Tue, Oct 4, 2016 at 2:09 PM, DuyHai Doan <doanduy...@gmail.com> wrote: > >> MV is right now your best choice for this kind of sorting behavior. >> >> Secondary index (whatever the impl, SASI or Lucene) has a cost of >> scatter-gather if your cluster scale out. With MV you're at least >> guaranteed to hit a single node everytime >> >> On Tue, Oct 4, 2016 at 1:56 PM, Dorian Hoxha <dorian.ho...@gmail.com> >> wrote: >> >>> Can you use the lucene index https://github.com/Stratio/cas >>> sandra-lucene-index ? >>> >>> On Tue, Oct 4, 2016 at 1:27 PM, Benjamin Roth <benjamin.r...@jaumo.com> >>> wrote: >>> >>>> Hi! >>>> >>>> I have a frequently used pattern which seems to be quite costly in CS. >>>> The pattern is always the same: I have a unique key and a sorting by a >>>> different field. >>>> >>>> To give an example, here a real life example from our model: >>>> CREATE TABLE visits.visits_in ( >>>> user_id int, >>>> user_id_visitor int, >>>> created timestamp, >>>> PRIMARY KEY (user_id, user_id_visitor) >>>> ) WITH CLUSTERING ORDER BY (user_id_visitor ASC) >>>> >>>> CREATE MATERIALIZED VIEW visits.visits_in_sorted_mv AS >>>> SELECT user_id, created, user_id_visitor >>>> FROM visits.visits_in >>>> WHERE user_id IS NOT NULL AND created IS NOT NULL AND >>>> user_id_visitor IS NOT NULL >>>> PRIMARY KEY (user_id, created, user_id_visitor) >>>> WITH CLUSTERING ORDER BY (created DESC, user_id_visitor DESC) >>>> >>>> This simply represents people, that visited my profile sorted by date >>>> desc but only one entry per visitor. >>>> Other examples with the same pattern could be a whats-app-like inbox >>>> where the last message of each sender is shown by date desc. There are lots >>>> of examples for that pattern. >>>> >>>> E.g. in redis I'd just use a sorted set, where the key could be like >>>> "visits_${user_id}", set key would be user_id_visitor and score >>>> the created timestamp. >>>> In MySQL I'd create the table with PK on user_id + user_id_visitor and >>>> create an index on user_id + created >>>> In C* i use an MV. >>>> >>>> Is this the most efficient approach? >>>> I also could have done this without an MV but then the situation in our >>>> app would be far more complex. >>>> I know that denormalization is a common pattern in C* and I don't >>>> hesitate to use it but in this case, it is not as simple as it's not an >>>> append-only case but updates have to be handled correctly. >>>> If it is the first visit of a user, it's that simple, just 2 inserts in >>>> base table + denormalized table. But on a 2nd or 3rd visit, the 1st or 2nd >>>> visit has to be deleted from the denormalized table before. Otherwise the >>>> visit would not be unique any more. >>>> Handling this case without an MV requires a lot more effort, I guess >>>> even more effort than just using an MV. >>>> 1. You need kind of app-side locking to deal with race conditions >>>> 2. Read before write is required to determine if an old record has to >>>> be deleted >>>> 3. At least CL_QUORUM is required to make sure that read before write >>>> is always consistent >>>> 4. Old record has to be deleted on update >>>> >>>> I guess, using an MV here is more efficient as there is less roundtrip >>>> between C* and the app to do all that and the MV does not require strong >>>> consistency as MV updates are always local and are eventual consistent when >>>> the base table is. So there is also no need for distributed locks. >>>> >>>> I ask all this as we now use CS 3.x and have been advised that 3.x is >>>> still not considered really production ready. >>>> >>>> I guess in a perfect world, this wouldn't even require an MV if SASI >>>> indexes could be created over more than 1 column. E.g. in MySQL this case >>>> is nothing else than a BTree. AFAIK SASI indices are also BTrees, filtering >>>> by Partition Key (which should to be done anyway) and sorting by a field >>>> would perfectly do the trick. But from the docs, this is not possible right >>>> now. >>>> >>>> Does anyone see a better solution or are all my assumptions correct? >>>> >>>> -- >>>> Benjamin Roth >>>> Prokurist >>>> >>>> Jaumo GmbH · www.jaumo.com >>>> Wehrstraße 46 · 73035 Göppingen · Germany >>>> Phone +49 7161 304880-6 · Fax +49 7161 304880-1 >>>> AG Ulm · HRB 731058 · Managing Director: Jens Kammerer >>>> >>> >>> >> >
