Hi Igor, 1. I still think we should do this. Loading nothing is very counterintuitive and prevents a newbie user from quick start. For large tables, when only part of the dataset is needed, user will explicitly specify the query, of course. Do you have objections? If no, I will create a ticket.
2. Got it, thanks. -Val On Mon, Oct 10, 2016 at 12:12 AM, Igor Rudyak <irud...@gmail.com> wrote: > Hi Val, > > 1) Well, it's not a problem to implement such default behavior, but there > is one concern. In most cases, when you are using Cassandra as a persistent > store you are going to store large amount of data, which is significantly > bigger that amount of RAM in your Ignite cluster. In the such case it > doesn't make sense to launch CQL query like "select * from my_table" cause: > a) You still will not be able to keep all data from Cassandra table in > Ignite cache > b) All the data will be pulled from Cassandra table using only one > thread - which is very slow > > 2) Unfortunately it's not possible in Cassandra. For JDBC you are > splitting table into chunks of 512 rows each, using sub-queries and > ordering by primary keys. Such kind of things are not supported in > Cassandra. Probably the only way to load data from Cassandra table in > parallel, is to load it from some specified partitions (in parallel for > each partition). > > > Igor Rudyak > > On Fri, Oct 7, 2016 at 1:45 PM, Valentin Kulichenko < > valentin.kuliche...@gmail.com> wrote: > >> Hi Igor, >> >> Thanks for response! >> >> 1. It's a bit inconsistent with other store implementations we have in >> the product and actually I find this counterintuitive. Why don't we just >> load all the data available in the table? Explicit query is useful when you >> want to customize this and load subset of data based on some criteria. If >> this is not possible for some reason, then I would at least throw an >> exception in case query is not specified. >> >> 2. Is it possible to automatically split the data in bulks and load them >> in parallel? We do this in the JDBC store, for example. >> >> -Val >> >> On Thu, Oct 6, 2016 at 11:00 PM, Igor Rudyak <irud...@gmail.com> wrote: >> >>> Hi Val, >>> >>> 1) If you'll call loadCache(null) it will do nothing. You need to >>> provide at least one CQL query. >>> >>> 2) It depends. If you'll provide more than one CQL query, it will use >>> separate thread for each of the queries (max number of threads limited to >>> the number of CPU cores). But for each provided CQL query it will use only >>> one thread to load all the data returned by the query. Also it will run the >>> same CQL query from ALL Ignite nodes to load the same data, which is bad. >>> That's because loadCache method will be executed on each Ignite node. As >>> you see, it's not very efficient way to load data from Cassandra just by >>> specifying CQL query. The ticket I created, is all about how to load data >>> from one table (or from multiple tables as well) in parallel by >>> partitioning it. Such a way each Ignite node will be responsible to load >>> data from the specific partition range of Cassandra table, which is much >>> more efficient. To support such kind of cache warm-up you should design >>> your Cassandra table specific way - there should be some mapping from >>> Ignite partition to the set of Cassandra partitions. Yes I have plans to >>> implement this. >>> >>> Igor Rudyak >>> >>> >>> On Thu, Oct 6, 2016 at 10:19 AM, Valentin Kulichenko < >>> valentin.kuliche...@gmail.com> wrote: >>> >>>> Hi Igor, >>>> >>>> I've got couple of quick questions about the Cassandra store. >>>> >>>> 1. In [1] you suggested to provide an explicit query as a parameter >>>> for loadCache() method, because otherwise user was always getting empty >>>> result. Is this a requirement to provide the query? What if I just call >>>> loadCache(null)? >>>> 2. There is a ticket [2] about parallel load in Cassandra store. >>>> Does it mean that currently it loads only in a single threaded fashion? >>>> If >>>> so, do you have any plans to implement this improvement? >>>> >>>> [1] http://apache-ignite-users.70518.x6.nabble.com/Cannot-qu >>>> ery-on-a-cache-using-Cassandra-as-a-persistent-store-td7870.html >>>> [2] https://gridgain.freshdesk.com/helpdesk/tickets/2180 >>>> >>>> Thanks, >>>> Val >>>> >>> >>> >> >
