Re: Indexes on heterogeneous rows
Thanks, Jonathan. I think I understand now. To sum up: Everything would work, but if your only equality is on type (all the rest inequalities), it could be very inefficient. Is that right? On Thu, Apr 14, 2011 at 7:22 PM, Jonathan Ellis jbel...@gmail.com wrote: On Thu, Apr 14, 2011 at 6:48 AM, David Boxenhorn da...@taotown.com wrote: The reason why I put type first is that queries on type will always be an exact match, whereas the other clauses might be inequalities. Expression order doesn't matter, but as you imply, non-equalities can't be used in an index lookup and have to be checked in a nested loop phase afterwards. -- Jonathan Ellis Project Chair, Apache Cassandra co-founder of DataStax, the source for professional Cassandra support http://www.datastax.com
Re: Indexes on heterogeneous rows
Right. On Sun, Apr 17, 2011 at 4:23 AM, David Boxenhorn da...@taotown.com wrote: Thanks, Jonathan. I think I understand now. To sum up: Everything would work, but if your only equality is on type (all the rest inequalities), it could be very inefficient. Is that right? On Thu, Apr 14, 2011 at 7:22 PM, Jonathan Ellis jbel...@gmail.com wrote: On Thu, Apr 14, 2011 at 6:48 AM, David Boxenhorn da...@taotown.com wrote: The reason why I put type first is that queries on type will always be an exact match, whereas the other clauses might be inequalities. Expression order doesn't matter, but as you imply, non-equalities can't be used in an index lookup and have to be checked in a nested loop phase afterwards. -- Jonathan Ellis Project Chair, Apache Cassandra co-founder of DataStax, the source for professional Cassandra support http://www.datastax.com -- Jonathan Ellis Project Chair, Apache Cassandra co-founder of DataStax, the source for professional Cassandra support http://www.datastax.com
Re: Indexes on heterogeneous rows
Does the get_indexed_slice in 0.7.4 version already do thing that way? It seems always take the 1st indexed column with EQ. Or is it a new feature of coming 0.7.5 or 0.8? -邮件原件- 发件人: Jonathan Ellis [mailto:jbel...@gmail.com] 发送时间: 2011年4月15日 0:21 收件人: user@cassandra.apache.org 抄送: David Boxenhorn; aaron morton 主题: Re: Indexes on heterogeneous rows This should work reasonably well w/ 0.7 indexes. Cassandra tracks statistics on index selectivity, so it would plan that query as index lookup on e=5, then iterate over those results and return only rows that also have type=2. On Thu, Apr 14, 2011 at 5:33 AM, David Boxenhorn da...@taotown.com wrote: Thank you for your answer, and sorry about the sloppy terminology. I'm thinking of the scenario where there are a small number of results in the result set, but there are billions of rows in the first of your secondary indexes. That is, I want to do something like (not sure of the CQL syntax): select * where type=2 and e=5 where there are billions of rows of type 2, but some manageable number of those rows have e=5. As I understand it, secondary indexes are like column families, where each value is a column. So the billions of rows where type=2 would go into a single row of the secondary index. This sounds like a problem to me, is it? I'm assuming that the billions of rows that don't have column e at all (those rows of other types) are not a problem at all... On Thu, Apr 14, 2011 at 12:12 PM, aaron morton aa...@thelastpickle.com wrote: Need to clear up some terminology here. Rows have a key and can be retrieved by key. This is *sort of* the primary index, but not primary in the normal RDBMS sense. Rows can have different columns and the column names are sorted and can be efficiently selected. There are secondary indexes in cassandra 0.7 based on column values http://www.datastax.com/dev/blog/whats-new-cassandra-07-secondary-indexes So you could create secondary indexes on the a,e, and h columns and get rows that have specific values. There are some limitations to secondary indexes, read the linked article. Or you can make your own secondary indexes using row keys as the index values. If you have billions of rows, how many do you need to read back at once? Hope that helps Aaron On 14 Apr 2011, at 04:23, David Boxenhorn wrote: Is it possible in 0.7.x to have indexes on heterogeneous rows, which have different sets of columns? For example, let's say you have three types of objects (1, 2, 3) which each had three members. If your rows had the following pattern type=1 a=? b=? c=? type=2 d=? e=? f=? type=3 g=? h=? i=? could you index type as your primary index, and also index a, e, h as secondary indexes, to get the objects of that type that you are looking for? Would it work if you had billions of rows of each type? -- Jonathan Ellis Project Chair, Apache Cassandra co-founder of DataStax, the source for professional Cassandra support http://www.datastax.com
Re: Indexes on heterogeneous rows
Thank you for your answer, and sorry about the sloppy terminology. I'm thinking of the scenario where there are a small number of results in the result set, but there are billions of rows in the first of your secondary indexes. That is, I want to do something like (not sure of the CQL syntax): select * where type=2 and e=5 where there are billions of rows of type 2, but some manageable number of those rows have e=5. As I understand it, secondary indexes are like column families, where each value is a column. So the billions of rows where type=2 would go into a single row of the secondary index. This sounds like a problem to me, is it? I'm assuming that the billions of rows that don't have column e at all (those rows of other types) are not a problem at all... On Thu, Apr 14, 2011 at 12:12 PM, aaron morton aa...@thelastpickle.comwrote: Need to clear up some terminology here. Rows have a key and can be retrieved by key. This is *sort of* the primary index, but not primary in the normal RDBMS sense. Rows can have different columns and the column names are sorted and can be efficiently selected. There are secondary indexes in cassandra 0.7 based on column values http://www.datastax.com/dev/blog/whats-new-cassandra-07-secondary-indexes So you could create secondary indexes on the a,e, and h columns and get rows that have specific values. There are some limitations to secondary indexes, read the linked article. Or you can make your own secondary indexes using row keys as the index values. If you have billions of rows, how many do you need to read back at once? Hope that helps Aaron On 14 Apr 2011, at 04:23, David Boxenhorn wrote: Is it possible in 0.7.x to have indexes on heterogeneous rows, which have different sets of columns? For example, let's say you have three types of objects (1, 2, 3) which each had three members. If your rows had the following pattern type=1 a=? b=? c=? type=2 d=? e=? f=? type=3 g=? h=? i=? could you index type as your primary index, and also index a, e, h as secondary indexes, to get the objects of that type that you are looking for? Would it work if you had billions of rows of each type?
Indexes on heterogeneous rows
Is it possible in 0.7.x to have indexes on heterogeneous rows, which have different sets of columns? For example, let's say you have three types of objects (1, 2, 3) which each had three members. If your rows had the following pattern type=1 a=? b=? c=? type=2 d=? e=? f=? type=3 g=? h=? i=? could you index type as your primary index, and also index a, e, h as secondary indexes, to get the objects of that type that you are looking for? Would it work if you had billions of rows of each type?
