vi ./src/java/org/apache/cassandra/db/marshal/CompositeType.java 'end-of-component' byte should always be 0 for actual column name. * However, it can set to 1 for query bounds. This allows to query for the * equivalent of 'give me the full super-column'. That is, if during a slice * query uses: * start = <3><"foo".getBytes()><0> * end = <3><"foo".getBytes()><1>
So with composites columns you can do: scf [b][1][*] by setting the start and end component. But you can not do scf [b][1][*] scf [b][7][*] in a single operation with composites. You seen to say you can query for a list of supercolumns, I am not sure how this works because the ColumnParent seems to only accept a single SuperColumn, but if you can do it I am not calling you a liar. Maybe this is a good case for 'server side scanners'. Ow man I know jbellis read this and put my face up on a dart board. On 12/29/11, Aditya <ady...@gmail.com> wrote: > On Fri, Dec 30, 2011 at 1:42 AM, Edward Capriolo > <edlinuxg...@gmail.com>wrote: > >> Hum... >> >> Do you have this? >> scf [b][1][a]=value >> scf [b][1][x]=value >> scf [b][7][b]=value >> >> and you want to slice: >> scf [b][1][*] >> >> Which would result in >> >> scf [b][1][a]=value >> scf [b][1][x]=value >> >> ? >> > > Exactly I have this! > And as for the queries, I want to retrieve columns (satisfying from a list > of wildcard names) , something like below : > > scf [b][1][*] > scf [b][7][*] > > Now this type of queries are not possible with composite columns but it is > very easily achievable through use of supercolumns, i can simply query for > a list of supercolumns(with entire subcolumns) by name. Right? > > So this is easier in terms of designing a query but since I don't > understand much about the internals and all, I am not sure if this is best > option for me, though by looking at my retrieval needs I feel somewhat > biased towards using supercolumns. > >> >> The composite version of this would be: >> cf [b][1:a]=value >> cf [b][1:x]=value >> cf [b][7:b]=value >> >> I am not sure exactly what you are doing because A SlicePredicate >> takes either a list of columns or a SliceRange. A ColumnPath takes a >> Single SuperColumn. >> >> I do not see how this is done with Columns or SuperColumns. Maybe you >> can provide a code snippet and/or some sample data? >> >> On 12/29/11, Aditya <ady...@gmail.com> wrote: >> > @Edward: Perhaps you missed to notice that I need to always retrieve >> > 'all >> > columns' under the supercolumn at any time.. and as per my query >> > requirements if I use composite columns instead of supercolumns then it >> is >> > impossible to do wildcard queries like the ones asked in this thread's >> > headline but which is much easier to do through the use of supercolumns. >> > >> > On Thu, Dec 29, 2011 at 11:06 PM, Edward Capriolo >> > <edlinuxg...@gmail.com>wrote: >> > >> >> The use case in question was: Only accessing some columns. >> >> >> >> Even if that is not the case: >> >> >> >> SuperColumns: 1 extra level of nesting >> >> Composite Colunns: Arbitrary levels of nesting >> >> >> >> SuperColumns: More overhead (space on disk) then using your own >> delimiter >> >> '_' >> >> SuperColumns: Likely going to be replaced in future c* version behind >> >> the scenes by composite columns anyway >> >> SuperColumns: Usually an afterthought for API developers, (support for >> >> them comes "later") >> >> SuperColumns: Almost always utilized incorrectly by users, users speak >> >> of '10%' performance gains after they switch away from them. >> >> >> >> There are some (a small % of cases) where SuperColumns are a better >> >> choice, but this is rare. With composites and concatenating columns >> >> they have no great purpose any more, (bad analogy coming!) like a >> >> mechanical type writer. >> >> >> >> On 12/29/11, Philippe <watche...@gmail.com> wrote: >> >> > Would you stand by that statement in case all colums inside the super >> >> > column need to be read? Why? >> >> > >> >> > Thanks >> >> > Le 28 déc. 2011 19:26, "Edward Capriolo" <edlinuxg...@gmail.com> a >> >> écrit : >> >> > >> >> >> Super columns have the same fundamental problem and perform worse in >> >> >> general. So switching from composites to super columns is NEVER a >> good >> >> >> idea. >> >> >> >> >> >> >> >> >> On Wed, Dec 28, 2011 at 1:19 PM, Aditya <ady...@gmail.com> wrote: >> >> >> >> >> >>> Since I have around 20 items to query, I guess making 20 queries to >> >> >>> retrieve activities by all followies on all of those 20 columns >> would >> >> too >> >> >>> inefficient, so to take the advantage of more efficient queries, >> >> >>> are >> >> >>> supercolumns recommended for this case ? Anyways, in case I use >> >> >>> supercolumns, I need to retrieve the entire supercolumn at any >> >> >>> point >> >> >>> of >> >> >>> time & I am writing subcolumn(s) to the supercolumn at different >> times >> >> >>> not >> >> >>> at once. >> >> >>> >> >> >>> On Wed, Dec 28, 2011 at 8:07 PM, Edward Capriolo >> >> >>> <edlinuxg...@gmail.com>wrote: >> >> >>> >> >> >>>> You need to execute one get slice operation for each item id or if >> >> >>>> the >> >> >>>> row is not large , you can try one large get slice on the entire >> row >> >> and >> >> >>>> deal with the results client side. >> >> >>>> >> >> >>>> If you try method 1 When doing slices on composites you can set >> >> >>>> the >> >> >>>> start inclusive or exclusive values to get only the column you >> >> >>>> want >> >> and >> >> >>>> not >> >> >>>> some extra columns up to slice range size. >> >> >>>> >> >> >>>> >> >> >>>> On Tuesday, December 27, 2011, Aditya <ady...@gmail.com> wrote: >> >> >>>> > I need to store data of all activities by user's followies in >> >> >>>> > single >> >> >>>> row. I am trying to do that making use of composite column names >> in a >> >> >>>> single user specific row named 'rowX'. >> >> >>>> > On any activity by a user's followie on an item, a column is >> stored >> >> in >> >> >>>> 'rowX'. The column has a composite type column name made up of >> >> >>>> itemId+userId (which makes it unique col. name) in rowX. (& column >> >> value >> >> >>>> contains the activity data related to that item by that followie) >> >> >>>> > >> >> >>>> > Now I want to retrieve activity by all users on a list of items. >> So >> >> I >> >> >>>> need to retrieve all composite columns with composite's first >> >> component >> >> >>>> matching the itemId. Is it possible to do such a query to >> Cassandra ? >> >> I >> >> >>>> am >> >> >>>> using Hector. >> >> >>>> >> >> >>> >> >> >>> >> >> >> >> >> > >> >> >> > >> >
