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From "Andrew Purtell (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (PHOENIX-838) Continuous queries
Date Tue, 06 May 2014 23:16:20 GMT

    [ https://issues.apache.org/jira/browse/PHOENIX-838?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13991313#comment-13991313
] 

Andrew Purtell commented on PHOENIX-838:
----------------------------------------

After PHOENIX-971, there might be a middle tier, with sufficient resources for tracking and
buffering streaming results, suitable to host this sort of function.

> Continuous queries
> ------------------
>
>                 Key: PHOENIX-838
>                 URL: https://issues.apache.org/jira/browse/PHOENIX-838
>             Project: Phoenix
>          Issue Type: New Feature
>            Reporter: Andrew Purtell
>
> Support continuous queries. 
> As a coprocessor application, Phoenix is well positioned to observe  mutations and treat
those observations as an event stream. 
> Continuous queries are persistent queries that run server side, typically expressed as
structured queries using some extensions for defining a bounded subset of a potentially unbounded
tuple stream. A Phoenix user could create a materialized view using WINDOW and other OLAP
extensions to SQL discussed on PHOENIX-154 to define time- or tuple- based sliding windows,
possibly partitioned, and an aggregating or filtering operation over those windows. This would
trigger instantiation of a long running distributed task on the cluster for incrementally
maintaining the view. ("Task" is meant here as a logical notion, it may not be a separate
thread of execution.) As the task receives observer events and performs work, it would update
state in memory for on-demand retrieval. For state reconstruction after failure the WAL could
be overloaded with in-window event history and/or the in-memory state could be periodically
checkpointed into shadow stores in the region.
> Users would pick up the latest state maintained by the continuous query by querying the
view, or perhaps Phoenix can do this transparently on any query if the optimizer determines
equivalence.
> This could be an important feature for Phoenix. Generally Phoenix and HBase are meant
to handle high data volumes that overwhelm other data management options, so even subsets
of the full data may present scale challenges. Many use cases mix ad hoc or exploratory full
table scans with aggregates, rollups, or sampling queries over a subset or sample. The user
wishes the latter queries to run as fast as possible. If that work can be done inline with
the process of initially persisting mutations then we trade some memory and CPU resources
up front to eliminate significant IO time later that would otherwise dominate.



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