Hi Ravi, With your suggested approach, I couldn't foresee any issues of the top of my head. Aaron has a more deeper understanding than I do, so he might be able to provide some insights regarding your approach. However, I would first validate that there is an advantage in terms of speed with your approach. Because the goal is to serve as much as possible from the block-cache and also we have a jira ticket to address performance when we have a cache miss (when the query has a fully qualified row-id, we should only search the shard which contains it). Thank You.
- Rahul On Mon, Sep 23, 2013 at 5:48 AM, Ravikumar Govindarajan < [email protected]> wrote: > Rahul, > > "When a search request is issued to the Blur Controller it searches > though all the shard servers in parallel and each shard server searches > through all of its shards. > Unlike database partitioning, I believe we cannot direct a search to a > particular shard. > However > 1. Upon shard server start, all the shards are warmed up ie Index > Reader's for each shard is loaded into memory > 2. Blur uses a block level cache. With sufficient memory allocated > to the cache, performance will be greatly enhanced" > > You are spot-on that what I was referring was a DB-Sharding like technique > and it definitely has some advantages, at least in our set-up. > > I think, what it translates in Blur, is to create N identical tables and > maintain user-wise mappings in our app. > > I mean lets say I create a table for every 10k users. I will end up with > 300 tables for 3 million users. What are the problems you foresee with that > large number of tables? I know for sure some K-V stores prohibit such an > approach. > > -- > Ravi > > > On Thu, Sep 19, 2013 at 11:16 PM, rahul challapalli < > [email protected]> wrote: > > > I will attempt to answer some of your questions below. Aaron or someone > > else can correct me if I am wrong > > > > > > On Thu, Sep 19, 2013 at 6:15 AM, Ravikumar Govindarajan < > > [email protected]> wrote: > > > > > Thanks Aaron. I think, it has answered my question. I have a few more > and > > > would be great if you can clarify them > > > > > > 1. Is the number of shards per-table fixed during table-creation or we > > can > > > dynamically allocate shards? > > > > > > > I believe we cannot dynamically allocate shards. The only thing we can > > dynamically add to an existing table is new columns > > > > > > > > 2. Assuming I have 10k shards with each shard-size=2GB, for a total of > 20 > > > TB table size. I typically use RowId = UserId and there are approx 3 > > > million users, in our system > > > > > > How do I ensure that when a user issues a query, I should not > end-up > > > searching all these 10k shards, but rather search only a very small set > > of > > > shards? > > > > > > > When a search request is issued to the Blur Controller it searches > > though all the shard servers in parallel and each shard server searches > > through all of its shards. > > Unlike database partitioning, I believe we cannot direct a search to > a > > particular shard. > > However > > 1. Upon shard server start, all the shards are warmed up ie Index > > Reader's for each shard is loaded into memory > > 2. Blur uses a block level cache. With sufficient memory > allocated > > to the cache, performance will be greatly enhanced > > > > > > > > > > 3. Are there any advantages of running shard-server and data-nodes > {HDFS} > > > in the same machine? > > > > > > Someone else can provide a better answer here. > > In a typical Hadoop installation Task Trackers and Data Nodes run > > alongside each other on the same machine. Since data nodes store the > first > > block replica on the > > same machine, shard servers might see an advantage in terms of > network > > latency. However I think it is not a good idea to run Blur alongside Task > > Trackers for > > performance reasons > > > > > > > > > -- > > > Ravi > > > > > > > > > On Thu, Sep 19, 2013 at 2:36 AM, Aaron McCurry <[email protected]> > > wrote: > > > > > > > I will attempt to answer below: > > > > > > > > On Wed, Sep 18, 2013 at 1:54 AM, Ravikumar Govindarajan < > > > > [email protected]> wrote: > > > > > > > > > Thanks a bunch for a concise and quick reply. Few more questions > > > > > > > > > > 1. Any pointers/links on how you plan to tackle the availability > > > problem? > > > > > > > > > > Lets say we store-forward hints to the failed shard-server. Won't > the > > > > HDFS > > > > > index-files differ in shard replicas? > > > > > > > > > > > > > I am in the process of documenting the strategy and will be adding it > > to > > > > JIRA soon. The way I am planning on solving this problem doesn't > > involve > > > > storing the indexes in more than once in HDFS (which of course is > > > > replicated). > > > > > > > > > > > > > > > > > > 2. I did not phrase my question on cross-join correctly. Let me > > clarify > > > > > > > > > > RowKey = 123 > > > > > > > > > > RecId = 1000 > > > > > Family = "ACCOUNTS" > > > > > Col-Name = "NAME" > > > > > Col-Value = "ABC" > > > > > ...... > > > > > > > > > > RecId = 1001 > > > > > Family = "CONTACTS" > > > > > Col-Name = "NAME" > > > > > Col-Value = "XYZ" > > > > > Col-Name = "ACCOUNTS-NAME" [FK to RecId=1000] > > > > > Col-Value = "1000" > > > > > ....... > > > > > > > > > > Lets say the user specifies the search query as > > > > > key=123 AND name:(ABC OR XYZ) > > > > > > > > > > Initially I will apply this query to each of the Family types, > namely > > > > > "ACCOUNTS", "CONTACTS" etc.... and get their RecIds.. > > > > > > > > > > After this, I will have to filter "CONTACTS" family results, based > on > > > > > RecIds received from "ACCOUNTS" [Join within records of different > > > family, > > > > > based on FK] > > > > > > > > > > Is something like this achievable? Can I design it differently to > > > satisfy > > > > > my requirements? > > > > > > > > > > > > > I may not fully understand your scenario. > > > > > > > > As I understand your example above: > > > > > > > > Row { > > > > "id" => "123", > > > > "records" => [ > > > > Record { > > > > "recordId" => "1000", "family" => "accounts", > > > > "columns" => [Column {"name" => "abc"}] > > > > }, > > > > Record { > > > > "recordId" => "1001", "family" => "contacts", > > > > "columns" => [Column {"name" => "abc"}] > > > > } > > > > ] > > > > } > > > > > > > > Let me go through some example queries that we support: > > > > > > > > +<accounts.name:abc> +<contacts.name:abc> > > > > > > > > Another way of writing it would be: > > > > > > > > <accounts.name:abc> AND <contacts.name:abc> > > > > > > > > Would yield a hit on the Row, there aren't any FKs in Blur. > > > > > > > > However if there are some interesting queries that be done with more > > > > examples: > > > > > > > > Row { > > > > "id" => "123", > > > > "records" => [ > > > > Record { > > > > "recordId" => "1000", "family" => "accounts", > > > > "columns" => [Column {"name" => "abc"}] > > > > }, > > > > Record { > > > > "recordId" => "1001", "family" => "contacts", > > > > "columns" => [Column {"name" => "abc"}] > > > > } > > > > ] > > > > } > > > > > > > > Row { > > > > "id" => "456", > > > > "records" => [ > > > > Record { > > > > "recordId" => "1000", "family" => "accounts", > > > > "columns" => [Column {"name" => "abc"}] > > > > }, > > > > Record { > > > > "recordId" => "1001", "family" => "contacts", > > > > "columns" => [Column {"name" => "abc"}] > > > > }, > > > > Record { > > > > "recordId" => "1002", "family" => "contacts", > > > > "columns" => [Column {"name" => "def"}] > > > > } > > > > ] > > > > } > > > > > > > > > > > > Row { > > > > "id" => "789", > > > > "records" => [ > > > > Record { > > > > "recordId" => "1000", "family" => "accounts", > > > > "columns" => [Column {"name" => "abc"}] > > > > }, > > > > Record { > > > > "recordId" => "1002", "family" => "contacts", > > > > "columns" => [Column {"name" => "def"}] > > > > } > > > > ] > > > > } > > > > > > > > For the given query: "<accounts.name:abc> AND <contacts.name:abc>" > > would > > > > yield 2 Row hits. 123 and 456 > > > > For the given query: "<accounts.name:abc> AND <contacts.name:def>" > > would > > > > yield 2 Row hits. 456 and 789 > > > > For the given query: "<contacts.name:abc> AND <contacts.name:def>" > > would > > > > yield 1 Row hit of 456. NOTICE that the family is the same here > > > > "contacts". > > > > > > > > Also in Blur you can turn off the Row query and just query the > records. > > > > This would be your typical Document like access. > > > > > > > > I fear that this has not answered your question, so if it hasn't > please > > > let > > > > me know. > > > > > > > > Thanks! > > > > > > > > Aaron > > > > > > > > > > > > > > > > > > > > > > -- > > > > > Ravi > > > > > > > > > > > > > > > > > > > > On Tue, Sep 17, 2013 at 7:01 PM, Aaron McCurry <[email protected] > > > > > > wrote: > > > > > > > > > > > First off let me say welcome! Hopefully I can answer your > > questions > > > > > inline > > > > > > below. > > > > > > > > > > > > > > > > > > On Tue, Sep 17, 2013 at 6:52 AM, Ravikumar Govindarajan < > > > > > > [email protected]> wrote: > > > > > > > > > > > > > I am quite new to Blur and need some help with the following > > > > questions > > > > > > > > > > > > > > 1. Lets say I have a replication_factor=3 for all HDFS indexes. > > In > > > > case > > > > > > one > > > > > > > of the server hosting HDFS indexes goes down [temporary or > > > > take-down], > > > > > > what > > > > > > > will happen to writes? Some kind-of HintedHandoff [as in > > Cassandra] > > > > is > > > > > > > supported? > > > > > > > > > > > > > > > > > > > When there is a Blur Shard Server failure state in ZooKeeper will > > > > change > > > > > > and the other shard servers will take action to bring the down > > > shard(s) > > > > > > online. This is similar to the HBase region model. While the > > > shard(s) > > > > > are > > > > > > being relocated (which really means being reopened from HDFS) > > writes > > > to > > > > > the > > > > > > shard(s) being moved are not available. However the bulk load > > > > capability > > > > > > is always available as long as HDFS is available, this can be > used > > > > > through > > > > > > Hadoop MapReduce. > > > > > > > > > > > > > > > > > > > > > > > > > > To re-phrase, what is the Consistency Vs Availability trade-off > > in > > > > > Blur, > > > > > > > with replication_factor>1 for HDFS indexes? > > > > > > > > > > > > > > > > > > > Of the two Consistency is favored over Availability, however we > are > > > > > > starting development (in 0.3.0) to increase availability during > > > > failures. > > > > > > > > > > > > > > > > > > > > > > > > > > 2. Since HDFSInputStream is used underneath, will this result > in > > > too > > > > > much > > > > > > > of data-transfer back-and-forth? A case of multi-segment-merge > or > > > > even > > > > > > > wild-card search could trigger it. > > > > > > > > > > > > > > > > > > > Blur uses an in process file system cache (Block Cache is the > term > > > used > > > > > in > > > > > > the code) to reduce the IO from HDFS. During index merges data > > that > > > is > > > > > not > > > > > > in the Block Cache is read from HDFS and the output is written > back > > > to > > > > > > HDFS. Overall once an index is hot (been online for some time) > the > > > IO > > > > > for > > > > > > any given search is fairly small assuming that the cluster has > > enough > > > > > > memory configured in the Block Cache. > > > > > > > > > > > > > > > > > > > > > > > > > > 3. Does Blur also support foreign-key like semantics to search > > > across > > > > > > > column-families as well as delete using row_id? > > > > > > > > > > > > > > > > > > > Blur supports something called Row Queries that allow for > searches > > > > across > > > > > > column families within single Rows. Take a look at this page > for a > > > > > better > > > > > > explanation: > > > > > > > > > > > > > > http://incubator.apache.org/blur/docs/0.2.0/data-model.html#querying > > > > > > > > > > > > And yes Blur supports deletes by Row check out: > > > > > > > > > > > > > > http://incubator.apache.org/blur/docs/0.2.0/Blur.html#Fn_Blur_mutate > > > > > > and > > > > > > > > > > > > http://incubator.apache.org/blur/docs/0.2.0/Blur.html#Struct_RowMutation > > > > > > > > > > > > Hopefully this can answer so of your questions. Let us know if > you > > > > have > > > > > > any more. > > > > > > > > > > > > Thanks, > > > > > > Aaron > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > -- > > > > > > > Ravi > > > > > > > > > > > > > > > > > > > > > > > > > > > >
