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From Aaron McCurry <amccu...@gmail.com>
Subject Re: Index Warmup in Blur
Date Fri, 04 Oct 2013 20:26:34 GMT
On Fri, Oct 4, 2013 at 7:15 AM, Ravikumar Govindarajan <
ravikumar.govindarajan@gmail.com> wrote:

> On a related note, do you think such an approach will fit in Blur
>
> 1. Store the BDB file in shard-server itself.
>

Probably not, this would pin the BDB (or whatever the solution would be) to
a specific server.  We will have to sync to HDFS.


>
> 2. Apply all incoming partial doc-updates to local BDB file as well as an
>     update-transaction log
>

Blur already has a write ahead log as apart of internals.  It's written and
synced to HDFS.


>
> 3. Periodically sync dirty BDB files to HDFS and roll-over the update-
>  transaction log.


> Whenever a shard-server goes down, the take-over server can initially sync
> the BDB file from HDFS to local, replay the update-transaction log and then
> start serving data
>

Blur already does this internally, it records the mutates and replays them
if a failure happens before a commit.

Aaron


>
> --
> Ravi
>
>
> On Thu, Oct 3, 2013 at 11:14 PM, Ravikumar Govindarajan <
> ravikumar.govindarajan@gmail.com> wrote:
>
> > The mutate APIs are a good fit for individual cols update. BlurCodec will
> > be cool and solve a lot of problems.
> >
> > There are 3 caveats for such a codec
> >
> > 1. Scores for affected queries will be wrong, until segment-merge
> >
> > 2. Responsibility of ordering updates must be on the client.
> >
> > 3. Repeated updates for the same document can either take a generational
> > approach [Lucene-4258] or use a single version of storage [Redis/TC
> etc..],
> > pushing the onus to client, depending on how the Codec shapes up.
> >
> > The former will be semantically correct but really sluggish while the
> > latter will be faster during search
> >
> >
> >
> > On Thu, Oct 3, 2013 at 8:53 PM, Aaron McCurry <amccurry@gmail.com>
> wrote:
> >
> >> On Thu, Oct 3, 2013 at 11:08 AM, Ravikumar Govindarajan <
> >> ravikumar.govindarajan@gmail.com> wrote:
> >>
> >> > Yeah, you are correct. A BDB file might probably never be ported to
> >> HDFS.
> >> >
> >> > Our daily update frequency comes to about 20% of insertion rate.
> >> >
> >> > Lets say "UPDATE <TABLE> SET COL2=1 WHERE COL1=X".
> >> >
> >> > This update could potentially span across tens of thousands of SQL
> rows
> >> in
> >> > our case, where COL2 is just a boolean flip.
> >> >
> >> > The problem is not with lucene's ability to handle load. Instead it is
> >> with
> >> > the consistent load it puts on our content servers to read and
> >> re-tokenize
> >> > such huge rows just for a boolean flip. Another big winner is that all
> >> our
> >> > updatable fields are not involved in scoring at all. Just matching
> will
> >> do.
> >> >
> >> > The changes also sit in BDB only till the next segment merge, after
> >> which
> >> > it is cleaned out. There is very little perf hit here for us, as users
> >> > don't immediately search after a change.
> >> >
> >> > I am afraid there is no documentation/code/numbers on this currently
> in
> >> > public, as it is still proprietary but is remarkably similar to the
> >> popular
> >> > to RedisCodec.
> >> >
> >> > "If you really need partial document updates, there would need to be
> >> > changes
> >> > throughout the entire stack"
> >> >
> >> > You mean, the entire stack of Blur? In case this is possible, can you
> >> give
> >> > me 10000-ft overview of what you have in mind?
> >> >
> >>
> >> Interesting, now that I think about it.  The situation that you describe
> >> is
> >> very interesting, I'm wondering if we came up with something like this
> in
> >> Blur that it would fix our large Row issue.  Or at the very least help
> the
> >> problem.
> >>
> >> https://issues.apache.org/jira/browse/BLUR-220
> >>
> >> Plus the more I think about it, the mutate methods are probably the
> right
> >> implementation for modifying single columns.  So the API of Blur
> probably
> >> wouldn't need to be changed.  Maybe just the way it goes about dealing
> >> with
> >> changes.  I thinking maybe we need our own BlurCodec to handle large
> Rows
> >> as well as Record (Document) updates.
> >>
> >> As an aside I constantly am having to refer to Records as Documents,
> this
> >> is why I think we need a rename.
> >>
> >> Aaron
> >>
> >>
> >>
> >>
> >>
> >>
> >> >
> >> > --
> >> > Ravi
> >> >
> >> >
> >> > On Thu, Oct 3, 2013 at 5:36 PM, Aaron McCurry <amccurry@gmail.com>
> >> wrote:
> >> >
> >> > > The biggest issue with this is that the shards (the indexes) inside
> of
> >> > Blur
> >> > > actually move from one server to another.  So to support this
> behavior
> >> > all
> >> > > the indexes are stored in HDFS.  Do due the differences between HDFS
> >> and
> >> > > the a normal POSIX file system, I highly doubt that the BDB file
> form
> >> in
> >> > > TokyoCabinet can ever be supported.
> >> > >
> >> > > If you really need partial document updates, there would need to be
> >> > changes
> >> > > throughout the entire stack.  I am curious why you need this
> feature?
> >>  Do
> >> > > you have that many updates to the index?  What is the update
> >> frequency?
> >> > >  I'm just curious of what kind of performance you get out of a setup
> >> like
> >> > > that?  Since I haven't ever run such a setup I have no idea how to
> >> > compare
> >> > > that kind of system to a base Lucene setup.
> >> > >
> >> > > Could you point be to some code or documentation?  I would to go and
> >> > take a
> >> > > look.
> >> > >
> >> > > Thanks,
> >> > > Aaron
> >> > >
> >> > >
> >> > >
> >> > > On Thu, Oct 3, 2013 at 7:00 AM, Ravikumar Govindarajan <
> >> > > ravikumar.govindarajan@gmail.com> wrote:
> >> > >
> >> > > > One more help.
> >> > > >
> >> > > > We also maintain a file by name "BDB", just like the "Sample"
file
> >> for
> >> > > > tracing used by Blur.
> >> > > >
> >> > > > This "BDB" file pertains to TokyoCabinet and is used purely for
> >> > > supporting
> >> > > > partial updates to a document.
> >> > > > All operations on this file rely on local file-paths only, through
> >> the
> >> > > use
> >> > > > of native code.
> >> > > > Currently, all update requests are local to the index files and
it
> >> > > becomes
> >> > > > trivial to support.
> >> > > >
> >> > > > Any pointers on how to take this forward in Blur set-up of
> >> > shard-servers
> >> > > &
> >> > > > controllers?
> >> > > >
> >> > > > --
> >> > > > Ravi
> >> > > >
> >> > > >
> >> > > > On Tue, Oct 1, 2013 at 10:15 PM, Aaron McCurry <
> amccurry@gmail.com>
> >> > > wrote:
> >> > > >
> >> > > > > You can control the fields to warmup via:
> >> > > > >
> >> > > > >
> >> > > > >
> >> > > >
> >> > >
> >> >
> >>
> http://incubator.apache.org/blur/docs/0.2.0/Blur.html#Struct_TableDescriptor
> >> > > > >
> >> > > > > The preCacheCols field.  The comment is wrong however, so
I will
> >> > > create a
> >> > > > > task to correct.  The use of the field is: "family.column"
just
> >> like
> >> > > you
> >> > > > > would search.
> >> > > > >
> >> > > > > Aaron
> >> > > > >
> >> > > > >
> >> > > > > On Tue, Oct 1, 2013 at 12:41 PM, Ravikumar Govindarajan
<
> >> > > > > ravikumar.govindarajan@gmail.com> wrote:
> >> > > > >
> >> > > > > > Thanks Aaron
> >> > > > > >
> >> > > > > > General sampling and warming is fine and the code is
really
> >> concise
> >> > > and
> >> > > > > > clear.
> >> > > > > >
> >> > > > > >  The act of reading
> >> > > > > > brings the data into the block cache and the result
is that
> the
> >> > index
> >> > > > is
> >> > > > > > "hot".
> >> > > > > >
> >> > > > > > Will all the terms of a field be read and brought into
the
> >> cache?
> >> > If
> >> > > > so,
> >> > > > > > then it has an obvious implication to avoid fields
like, say
> >> > > > > > attachment-data from warming up, provided queries don't
often
> >> > include
> >> > > > > such
> >> > > > > > fields
> >> > > > > >
> >> > > > > >
> >> > > > > > On Tue, Oct 1, 2013 at 7:58 PM, Aaron McCurry <
> >> amccurry@gmail.com>
> >> > > > > wrote:
> >> > > > > >
> >> > > > > > > Take a look at this package.
> >> > > > > > >
> >> > > > > > >
> >> > > > > > >
> >> > > > > >
> >> > > > >
> >> > > >
> >> > >
> >> >
> >>
> https://git-wip-us.apache.org/repos/asf?p=incubator-blur.git;a=tree;f=blur-store/src/main/java/org/apache/blur/lucene/warmup;h=f4239b1947965dc7fe8218eaa16e3f39ecffdda0;hb=apache-blur-0.2
> >> > > > > > >
> >> > > > > > > Basically when the warmup process starts (which
is
> >> asynchronous
> >> > to
> >> > > > the
> >> > > > > > rest
> >> > > > > > > of the application) it flips a thread local switch
to allow
> >> for
> >> > > > tracing
> >> > > > > > of
> >> > > > > > > the file accesses.  The sampler will sample each
of the
> >> fields in
> >> > > > each
> >> > > > > > > segment and create a sample file that attempts
to detect the
> >> > > > boundaries
> >> > > > > > of
> >> > > > > > > each field within each file within each segment.
 Then it
> >> stores
> >> > > the
> >> > > > > > sample
> >> > > > > > > info into the directory beside each segment (so
that way it
> >> > doesn't
> >> > > > > have
> >> > > > > > to
> >> > > > > > > re-sample the segment).  After the sampling is
complete or
> >> > loaded,
> >> > > > the
> >> > > > > > > warmup just reads the binary data from each file.
 The act
> of
> >> > > reading
> >> > > > > > > brings the data into the block cache and the result
is that
> >> the
> >> > > index
> >> > > > > is
> >> > > > > > > "hot".
> >> > > > > > >
> >> > > > > > > Hope this helps.
> >> > > > > > >
> >> > > > > > > Aaron
> >> > > > > > >
> >> > > > > > >
> >> > > > > > >
> >> > > > > > >
> >> > > > > > > On Tue, Oct 1, 2013 at 10:09 AM, Ravikumar Govindarajan
<
> >> > > > > > > ravikumar.govindarajan@gmail.com> wrote:
> >> > > > > > >
> >> > > > > > > > As I understand,
> >> > > > > > > >
> >> > > > > > > > Lucene will store the files in following
way per-segment
> >> > > > > > > >
> >> > > > > > > > TIM file
> >> > > > > > > >      Field1 ---> Some byte[]
> >> > > > > > > >      Field2 ---> Some byte[]
> >> > > > > > > >
> >> > > > > > > > TIP file
> >> > > > > > > >      Field1 ---> Some byte[]
> >> > > > > > > >      Field2 ---> Some byte[]
> >> > > > > > > >
> >> > > > > > > >
> >> > > > > > > > Blur will "sample" this lucene-file in the
following way
> >> > > > > > > >
> >> > > > > > > > Field1 --> <TIM, start-offset>,
<TIP, start-offset>, ...
> >> > > > > > > >
> >> > > > > > > > Field 2 --> <TIM, start-offset>,
<TIP, start-offset>, ...
> >> > > > > > > >
> >> > > > > > > > Is my understanding correct?
> >> > > > > > > >
> >> > > > > > > > How does Blur warm-up the fields, when it
does not know
> the
> >> > > > > > "end-offset"
> >> > > > > > > or
> >> > > > > > > > the "length" for each field to warm.
> >> > > > > > > >
> >> > > > > > > > Will it by default read all Terms of a field?
> >> > > > > > > >
> >> > > > > > > > --
> >> > > > > > > > Ravi
> >> > > > > > > >
> >> > > > > > >
> >> > > > > >
> >> > > > >
> >> > > >
> >> > >
> >> >
> >>
> >
> >
>

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