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From Martin Koch <...@issuu.com>
Subject Re: SolrCloud and exernal file fields
Date Tue, 20 Nov 2012 22:07:27 GMT
Mikhail

PSB

On Tue, Nov 20, 2012 at 7:22 PM, Mikhail Khludnev <
mkhludnev@griddynamics.com> wrote:

> Martin,
>
> Please find additional question from me below.
>
> Simone,
>
> I'm sorry for hijacking your thread. The only what I've heard about it at
> recent ApacheCon sessions is that Zookeeper is supposed to replicate those
> files as configs under solr home. And I'm really looking forward to know
> how it works with huge files in production.
>
> Thank You, Guys!
>
> 20.11.2012 18:06 пользователь "Martin Koch" <mak@issuu.com> написал:
> >
> > Hi Mikhail
> >
> > Please see answers below.
> >
> > On Tue, Nov 20, 2012 at 12:28 PM, Mikhail Khludnev <
> > mkhludnev@griddynamics.com> wrote:
> >
> > > Martin,
> > >
> > > Thank you for telling your own "war-story". It's really useful for
> > > community.
> > > The first question might seems not really conscious, but would you tell
> me
> > > what blocks searching during EFF reload, when it's triggered by handler
> or
> > > by listener?
> > >
> >
> > We continuously index new documents using CommitWithin to get regular
> > commits. However, we observed that the EFFs were not re-read, so we had
> to
> > do external commits (curl '.../solr/update?commit=true') to force reload.
> > When this is done, solr blocks. I can't tell you exactly why it's doing
> > that (it was related to SOLR-3985).
>
> Is there a chance to get a thread dump when they are blocked?
>
>
Well I could try to recreate the situation. But the setup is fairly simple:
Create a large EFF in a largeish index with many shards. Issue a commit,
and then try to do a search. Solr will not respond to the search before the
commit has completed, and this will take a long time.


>
> >
> >
> > > I don't really get the sentence about sequential commits and number of
> > > cores. Do I get right that file is replicated via Zookeeper? Doesn't it
> > >
> >
> > Again, this is observed behavior. When we issue a commit on a system with
> a
> > system with many solr cores using EFFs, the system blocks for a long time
> > (15 minutes).  We do NOT use zookeeper for anything. The EFF is a symlink
> > from each cores index dir to the actual file, which is updated by an
> > external process.
>
> Hold on, I asked about Zookeeper because the subj mentions SolrCloud.
>
> Do you use SolrCloud, SolrShards, or these cores are just replicas of the
> same index?
>

Ah - we use solr 4 out of the box, so I guess this is SolrCloud. I'm a bit
unsure about the terminology here, but we've got a single index divided
into 16 shard. Each shard is hosted in a solr core.


> Also, about simlink - Don't you share that file via some NFS?
>
> No, we generate the EFF on the local solr host (there is only one physical
host that holds all shards), so there is no need for NFS or copying files
around. No need for Zookeeper either.


> how many cores you run per box?
>
This box is a 16-virtual core (8 hyperthreaded cores)  with 60GB of RAM. We
run 16 solr cores on this box in Jetty.


> Do boxes has plenty of ram to cache filesystem beside of jvm heaps?
>
> Yes. We've allocated 10GB for jetty, and left the rest for the OS.


> I assume you use 64 bit linux and mmap directory. Please confirm that.
>
>
We use 64-bit linux. I'm not sure about the mmap directory or where that
would be configured in solr - can you explain that?

>
> >
> >
> > > causes scalability problem or long time to reload? Will it help if
> we'll
> > > have, let's say ExternalDatabaseField which will pull values from jdbc.
> ie.
> > >
> >
> > I think the possibility of having some fields being retrieved from an
> > external, dynamically updatable store would be really interesting. This
> > could be JDBC, something in-memory like redis, or a NoSql product (e.g.
> > Cassandra).
>
> Ok. Let's have it in mind as a possible direction.
>

Alternatively, an API that would allow updating a single field for a
document might be an option.


>
> >
> >
> > > why all cores can't read these values simultaneously?
> > >
> >
> > Again, this is a solr implementation detail that I can't answer :)
> >
> >
> > > Can you confirm that IDs in the file is ordered by the index term
> order?
> > >
> >
> > Yes, we sorted the files (standard UNIX sort).
> >
> >
> > > AFAIK it can impact load time.
> > >
> > Yes, it does
>
> Ok, I've got that you aware of it, and your IDs are just strings, not
> integers.
>
>
Yes, ids are strings.

>
> >
> >
> > > Regarding your post-query solution can you tell me if query found 10000
> > > docs, but I need to display only first page with 100 rows, whether I
> need
> > > to pull all 10K results to frontend to order them by the rank?
> > >
> > >
> > In our architecture, the clients query an API that generates the SOLR
> > query, retrieves the relevant additional fields that we needs, and
> returns
> > the relevant JSON to the front-end.
> >
> > In our use case, results are returned from SOLR by the 10's, not by the
> > 1000's, so it is a manageable job. Even so, if solr returned thousands of
> > results, it would be up to the implementation of the api to augment only
> > the results that needed to be returned to the front-end.
> >
> > Even so, patching up a JSON structure with 10000 results should be
> > possible.
>
> You are right. I'm concerned anyway because retrieving whole result is
> expensive, and not always possible.
>
>
In our case, getting the whole result is almost impossible, because that
would be millions of documents, and returning the Nth result seems to be a
quadratic (or worse) operation in SOLR.

>
> >
> >
> > > I'm really appreciate if you comment on the questions above.
> > > PS: It's time to pitch, how much
> > > https://issues.apache.org/jira/browse/SOLR-4085 "Commit-free
> > > ExternalFileField" can help you?
> > >
> > >
> > > It looks very interesting :) Does it make it possible to avoid
> re-reading
> > the EFF on every commit, and only re-read the values that have actually
> > changed?
>
>
> You don't need commit (in SOLR-4085) to reload file content, but after
> commit you need to read whole file and scan all key terms and postings.
> That's because EFF sits on top of top level searcher. it's a Solr-like way.
> In some future we might have per-segment EFF, in this case adding a segment
> will trigger full file scan, but in the index only that new segment will be
> scanned. It should be faster. You know, straightforward sharing internal
> data structures between different index views/generations is not possible.
> If you are asking about applying delta changes on external file that's
> something what we did ourselves http://goo.gl/P8GFq . This feature is much
> more doubtful and vague, although it might be the next contribution after
> SOLR-4085.
>
> >
> > /Martin
> >
> >
> > >
> > > On Tue, Nov 20, 2012 at 1:16 PM, Martin Koch <mak@issuu.com> wrote:
> > >
> > > > Solr 4.0 does support using EFFs, but it might not give you what
> you're
> > > > hoping fore.
> > > >
> > > > We tried using Solr Cloud, and have given up again.
> > > >
> > > > The EFF is placed in the parent of the index directory in each core;
> each
> > > > core reads the entire EFF and picks out the IDs that it is
> responsible
> > > for.
> > > >
> > > > In the current 4.0.0 release of solr, solr blocks (doesn't answer
> > > queries)
> > > > while re-reading the EFF. Even worse, it seems that the time to
> re-read
> > > the
> > > > EFF is multiplied by the number of cores in use (i.e. the EFF is
> re-read
> > > by
> > > > each core sequentially). The contents of the EFF become active after
> the
> > > > first EXTERNAL commit (commitWithin does NOT work here) after the
> file
> > > has
> > > > been updated.
> > > >
> > > > In our case, the EFF was quite large - around 450MB - and we use 16
> > > shards,
> > > > so when we triggered an external commit to force re-reading, the
> whole
> > > > system would block for several (10-15) minutes. This won't work in a
> > > > production environment. The reason for the size of the EFF is that we
> > > have
> > > > around 7M documents in the index; each document has a 45 character
> ID.
> > > >
> > > > We got some help to try to fix the problem so that the re-read of the
> EFF
> > > > proceeds in the background (see
> > > > here<https://issues.apache.org/jira/browse/SOLR-3985> for
> > > > a fix on the 4.1 branch). However, even though the re-read proceeds
> in
> > > the
> > > > background, the time required to launch solr now takes at least as
> long
> > > as
> > > > re-reading the EFFs. Again, this is not good enough for our needs.
> > > >
> > > > The next issue is that you cannot sort on EFF fields (though you can
> > > return
> > > > them as values using &fl=field(my_eff_field). This is also fixed in
> the
> > > 4.1
> > > > branch here <https://issues.apache.org/jira/browse/SOLR-4022>.
> > > >
> > > > So: Even after these fixes, EFF performance is not that great. Our
> > > solution
> > > > is as follows: The actual value of the popularity measure (say,
> reads)
> > > that
> > > > we want to report to the user is inserted into the search response
> > > > post-query by our query front-end. This value will then be the
> > > > authoritative value at the time of the query. The value of the
> popularity
> > > > measure that we use for boosting in the ranking of the search results
> is
> > > > only updated when the value has changed enough so that the impact on
> the
> > > > boost will be significant (say, more than 2%). This does require
> frequent
> > > > re-indexing of the documents that have significant changes in the
> number
> > > of
> > > > reads, but at least we won't have to update a document if it moves
> from,
> > > > say, 1000000 to 1000001 reads.
> > > >
> > > > /Martin Koch - ISSUU - senior systems architect.
> > > >
> > > > On Mon, Nov 19, 2012 at 3:22 PM, Simone Gianni <simoneg@apache.org>
> > > wrote:
> > > >
> > > > > Hi all,
> > > > > I'm planning to move a quite big Solr index to SolrCloud. However,
> in
> > > > this
> > > > > index, an external file field is used for popularity ranking.
> > > > >
> > > > > Does SolrCloud supports external file fields? How does it cope with
> > > > > sharding and replication? Where should the external file be placed
> now
> > > > that
> > > > > the index folder is not local but in the cloud?
> > > > >
> > > > > Are there otherwise other best practices to deal with the use cases
> > > > > external file fields were used for, like popularity/ranking, in
> > > > SolrCloud?
> > > > > Custom ValueSources going to something external?
> > > > >
> > > > > Thanks in advance,
> > > > > Simone
> > > > >
> > > >
> > >
> > >
> > >
> > > --
> > > Sincerely yours
> > > Mikhail Khludnev
> > > Principal Engineer,
> > > Grid Dynamics
> > >
> > > <http://www.griddynamics.com>
> > >  <mkhludnev@griddynamics.com>
> > >
>  20.11.2012 18:06 пользователь "Martin Koch" <mak@issuu.com> написал:
>
> > Hi Mikhail
> >
> > Please see answers below.
> >
> > On Tue, Nov 20, 2012 at 12:28 PM, Mikhail Khludnev <
> > mkhludnev@griddynamics.com> wrote:
> >
> > > Martin,
> > >
> > > Thank you for telling your own "war-story". It's really useful for
> > > community.
> > > The first question might seems not really conscious, but would you tell
> > me
> > > what blocks searching during EFF reload, when it's triggered by handler
> > or
> > > by listener?
> > >
> >
> > We continuously index new documents using CommitWithin to get regular
> > commits. However, we observed that the EFFs were not re-read, so we had
> to
> > do external commits (curl '.../solr/update?commit=true') to force reload.
> > When this is done, solr blocks. I can't tell you exactly why it's doing
> > that (it was related to SOLR-3985).
> >
> >
> > > I don't really get the sentence about sequential commits and number of
> > > cores. Do I get right that file is replicated via Zookeeper? Doesn't it
> > >
> >
> > Again, this is observed behavior. When we issue a commit on a system
> with a
> > system with many solr cores using EFFs, the system blocks for a long time
> > (15 minutes).  We do NOT use zookeeper for anything. The EFF is a symlink
> > from each cores index dir to the actual file, which is updated by an
> > external process.
> >
> >
> > > causes scalability problem or long time to reload? Will it help if
> we'll
> > > have, let's say ExternalDatabaseField which will pull values from jdbc.
> > ie.
> > >
> >
> > I think the possibility of having some fields being retrieved from an
> > external, dynamically updatable store would be really interesting. This
> > could be JDBC, something in-memory like redis, or a NoSql product (e.g.
> > Cassandra).
> >
> >
> > > why all cores can't read these values simultaneously?
> > >
> >
> > Again, this is a solr implementation detail that I can't answer :)
> >
> >
> > > Can you confirm that IDs in the file is ordered by the index term
> order?
> > >
> >
> > Yes, we sorted the files (standard UNIX sort).
> >
> >
> > > AFAIK it can impact load time.
> > >
> > Yes, it does.
> >
> >
> > > Regarding your post-query solution can you tell me if query found 10000
> > > docs, but I need to display only first page with 100 rows, whether I
> need
> > > to pull all 10K results to frontend to order them by the rank?
> > >
> > >
> > In our architecture, the clients query an API that generates the SOLR
> > query, retrieves the relevant additional fields that we needs, and
> returns
> > the relevant JSON to the front-end.
> >
> > In our use case, results are returned from SOLR by the 10's, not by the
> > 1000's, so it is a manageable job. Even so, if solr returned thousands of
> > results, it would be up to the implementation of the api to augment only
> > the results that needed to be returned to the front-end.
> >
> > Even so, patching up a JSON structure with 10000 results should be
> > possible.
> >
> >
> > > I'm really appreciate if you comment on the questions above.
> > > PS: It's time to pitch, how much
> > > https://issues.apache.org/jira/browse/SOLR-4085 "Commit-free
> > > ExternalFileField" can help you?
> > >
> > >
> > > It looks very interesting :) Does it make it possible to avoid
> re-reading
> > the EFF on every commit, and only re-read the values that have actually
> > changed?
> >
> > /Martin
> >
> >
> > >
> > > On Tue, Nov 20, 2012 at 1:16 PM, Martin Koch <mak@issuu.com> wrote:
> > >
> > > > Solr 4.0 does support using EFFs, but it might not give you what
> you're
> > > > hoping fore.
> > > >
> > > > We tried using Solr Cloud, and have given up again.
> > > >
> > > > The EFF is placed in the parent of the index directory in each core;
> > each
> > > > core reads the entire EFF and picks out the IDs that it is
> responsible
> > > for.
> > > >
> > > > In the current 4.0.0 release of solr, solr blocks (doesn't answer
> > > queries)
> > > > while re-reading the EFF. Even worse, it seems that the time to
> re-read
> > > the
> > > > EFF is multiplied by the number of cores in use (i.e. the EFF is
> > re-read
> > > by
> > > > each core sequentially). The contents of the EFF become active after
> > the
> > > > first EXTERNAL commit (commitWithin does NOT work here) after the
> file
> > > has
> > > > been updated.
> > > >
> > > > In our case, the EFF was quite large - around 450MB - and we use 16
> > > shards,
> > > > so when we triggered an external commit to force re-reading, the
> whole
> > > > system would block for several (10-15) minutes. This won't work in a
> > > > production environment. The reason for the size of the EFF is that we
> > > have
> > > > around 7M documents in the index; each document has a 45 character
> ID.
> > > >
> > > > We got some help to try to fix the problem so that the re-read of the
> > EFF
> > > > proceeds in the background (see
> > > > here<https://issues.apache.org/jira/browse/SOLR-3985> for
> > > > a fix on the 4.1 branch). However, even though the re-read proceeds
> in
> > > the
> > > > background, the time required to launch solr now takes at least as
> long
> > > as
> > > > re-reading the EFFs. Again, this is not good enough for our needs.
> > > >
> > > > The next issue is that you cannot sort on EFF fields (though you can
> > > return
> > > > them as values using &fl=field(my_eff_field). This is also fixed in
> the
> > > 4.1
> > > > branch here <https://issues.apache.org/jira/browse/SOLR-4022>.
> > > >
> > > > So: Even after these fixes, EFF performance is not that great. Our
> > > solution
> > > > is as follows: The actual value of the popularity measure (say,
> reads)
> > > that
> > > > we want to report to the user is inserted into the search response
> > > > post-query by our query front-end. This value will then be the
> > > > authoritative value at the time of the query. The value of the
> > popularity
> > > > measure that we use for boosting in the ranking of the search results
> > is
> > > > only updated when the value has changed enough so that the impact on
> > the
> > > > boost will be significant (say, more than 2%). This does require
> > frequent
> > > > re-indexing of the documents that have significant changes in the
> > number
> > > of
> > > > reads, but at least we won't have to update a document if it moves
> > from,
> > > > say, 1000000 to 1000001 reads.
> > > >
> > > > /Martin Koch - ISSUU - senior systems architect.
> > > >
> > > > On Mon, Nov 19, 2012 at 3:22 PM, Simone Gianni <simoneg@apache.org>
> > > wrote:
> > > >
> > > > > Hi all,
> > > > > I'm planning to move a quite big Solr index to SolrCloud. However,
> in
> > > > this
> > > > > index, an external file field is used for popularity ranking.
> > > > >
> > > > > Does SolrCloud supports external file fields? How does it cope with
> > > > > sharding and replication? Where should the external file be placed
> > now
> > > > that
> > > > > the index folder is not local but in the cloud?
> > > > >
> > > > > Are there otherwise other best practices to deal with the use cases
> > > > > external file fields were used for, like popularity/ranking, in
> > > > SolrCloud?
> > > > > Custom ValueSources going to something external?
> > > > >
> > > > > Thanks in advance,
> > > > > Simone
> > > > >
> > > >
> > >
> > >
> > >
> > > --
> > > Sincerely yours
> > > Mikhail Khludnev
> > > Principal Engineer,
> > > Grid Dynamics
> > >
> > > <http://www.griddynamics.com>
> > >  <mkhludnev@griddynamics.com>
> > >
> >
>

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