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From Aaron McCurry <amccu...@gmail.com>
Subject Re: Index Warmup in Blur
Date Fri, 04 Oct 2013 20:31:05 GMT
I have thought of one possible problem with this approach.  To date the
mindset I have used in all of the Blur internals is that segments are
immutable.  This is a fundamental principle that Blur uses and I don't
really have any ideas on where to behind checking for when this is a
problem.  I know filters are going to be an issue, not sure where else.

Not saying that it can't be done, it's just not going to be as clean as I
originally thought.

Aaron


On Fri, Oct 4, 2013 at 4:26 PM, Aaron McCurry <amccurry@gmail.com> wrote:

>
>
> 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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