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From sgaron cse <sgaron....@gmail.com>
Subject Re: Realtime get not always returning existing data
Date Wed, 10 Oct 2018 14:53:06 GMT
I haven't found a way to reproduce the problem other that running our
entire set of code. I've also been trying different things to make sure to
problem is not from my end and so far I haven't managed to fix it by
changing my code. It has to be a race condition somewhere but I just can't
put my finger on it.

I'll message back if I find a way to reproduce.

On Wed, Oct 10, 2018 at 10:48 AM Erick Erickson <erickerickson@gmail.com>
wrote:

> Well assigning a bogus version that generates a 409 error then
> immediately doing an RTG on the doc doesn't fail for me either 18
> million tries later. So I'm afraid I haven't a clue where to go from
> here. Unless we can somehow find a way to generate this failure I'm
> going to drop it for the foreseeable future.
>
> Erick
> On Tue, Oct 9, 2018 at 7:39 AM Erick Erickson <erickerickson@gmail.com>
> wrote:
> >
> > Hmmmm. I wonder if a version conflict or perhaps other failure can
> > somehow cause this. It shouldn't be very hard to add that to my test
> > setup, just randomly add n _version_ field value.
> >
> > Erick
> > On Mon, Oct 1, 2018 at 8:20 AM Erick Erickson <erickerickson@gmail.com>
> wrote:
> > >
> > > Thanks. I'll be away for the rest of the week, so won't be able to try
> > > anything more....
> > > On Mon, Oct 1, 2018 at 5:10 AM Chris Ulicny <culicny@iq.media> wrote:
> > > >
> > > > In our case, we are heavily indexing in the collection while the /get
> > > > requests are happening which is what we assumed was causing this
> very rare
> > > > behavior. However, we have experienced the problem for a collection
> where
> > > > the following happens in sequence with minutes in between them.
> > > >
> > > > 1. Document id=1 is indexed
> > > > 2. Document successfully retrieved with /get?id=1
> > > > 3. Document failed to be retrieved with /get?id=1
> > > > 4. Document successfully retrieved with /get?id=1
> > > >
> > > > We've haven't looked at the issue in a while, so I don't have the
> exact
> > > > timing of that sequence on hand right now. I'll try to find an actual
> > > > example, although I'm relatively certain it was multiple minutes in
> between
> > > > each of those requests. However our autocommit (and soft commit)
> times are
> > > > 60s for both collections.
> > > >
> > > > I think the following two are probably the biggest differences for
> our
> > > > setup, besides the version difference (v6.3.0):
> > > >
> > > > > index to this collection, perhaps not at a high rate
> > > > > separate the machines running solr from the one doing any querying
> or
> > > > indexing
> > > >
> > > > The clients are on 3 hosts separate from the solr instances. The
> total
> > > > number of threads that are making updates and making /get requests is
> > > > around 120-150. About 40-50 per host. Each of our two collections
> gets an
> > > > average of 500 requests per second constantly for ~5 minutes, and
> then the
> > > > number slowly tapers off to essentially 0 after ~15 minutes.
> > > >
> > > > Every thread attempts to make the same series of requests.
> > > >
> > > > -- Update with "_version_=-1". If successful, no other requests are
> made.
> > > > -- On 409 Conflict failure, it makes a /get request for the id
> > > > -- On doc:null failure, the client handles the error and moves on
> > > >
> > > > Combining this with the previous series of /get requests, we end up
> with
> > > > situations where an update fails as expected, but the subsequent /get
> > > > request fails to retrieve the existing document:
> > > >
> > > > 1. Thread 1 updates id=1 successfully
> > > > 2. Thread 2 tries to update id=1, fails (409)
> > > > 3. Thread 2 tries to get id=1 succeeds.
> > > >
> > > > ...Minutes later...
> > > >
> > > > 4. Thread 3 tries to update id=1, fails (409)
> > > > 5. Thread 3 tries to get id=1, fails (doc:null)
> > > >
> > > > ...Minutes later...
> > > >
> > > > 6. Thread 4 tries to update id=1, fails (409)
> > > > 7. Thread 4 tries to get id=1 succeeds.
> > > >
> > > > As Steven mentioned, it happens very, very rarely. We tried to
> recreate it
> > > > in a more controlled environment, but ran into the same issue that
> you are,
> > > > Erick. Every simplified situation we ran produced no problems. Since
> it's
> > > > not a large issue for us and happens very rarely, we stopped trying
> to
> > > > recreate it.
> > > >
> > > >
> > > > On Sun, Sep 30, 2018 at 9:16 PM Erick Erickson <
> erickerickson@gmail.com>
> > > > wrote:
> > > >
> > > > > 57 million queries later, with constant indexing going on and 9
> dummy
> > > > > collections in the mix and the main collection I'm querying having
> 2
> > > > > shards, 2 replicas each, I have no errors.
> > > > >
> > > > > So unless the code doesn't look like it exercises any similar path,
> > > > > I'm not sure what more I can test. "It works on my machine" ;)
> > > > >
> > > > > Here's my querying code, does it look like it what you're seeing?
> > > > >
> > > > >       while (Main.allStop.get() == false) {
> > > > >         try (SolrClient client = new HttpSolrClient.Builder()
> > > > > //("http://my-solr-server:8981/solr/eoe_shard1_replica_n4")) {
> > > > >             .withBaseSolrUrl("http://localhost:8981/solr/eoe").build())
> {
> > > > >
> > > > >           //SolrQuery query = new SolrQuery();
> > > > >           String lower = Integer.toString(rand.nextInt(1_000_000));
> > > > >           SolrDocument rsp = client.getById(lower);
> > > > >           if (rsp == null) {
> > > > >             System.out.println("Got a null response!");
> > > > >             Main.allStop.set(true);
> > > > >           }
> > > > >
> > > > >           rsp = client.getById(lower);
> > > > >
> > > > >           if (rsp.get("id").equals(lower) == false) {
> > > > >             System.out.println("Got an invalid response, looking
> for "
> > > > > + lower + " got: " + rsp.get("id"));
> > > > >             Main.allStop.set(true);
> > > > >           }
> > > > >           long queries = Main.eoeCounter.incrementAndGet();
> > > > >           if ((queries % 100_000) == 0) {
> > > > >             long seconds = (System.currentTimeMillis() -
> Main.start) /
> > > > > 1000;
> > > > >             System.out.println("Query count: " +
> > > > > numFormatter.format(queries) + ", rate is " +
> > > > > numFormatter.format(queries / seconds) + " QPS");
> > > > >           }
> > > > >         } catch (Exception cle) {
> > > > >           cle.printStackTrace();
> > > > >           Main.allStop.set(true);
> > > > >         }
> > > > >       }
> > > > >   }On Sat, Sep 29, 2018 at 12:46 PM Erick Erickson
> > > > > <erickerickson@gmail.com> wrote:
> > > > > >
> > > > > > Steve:
> > > > > >
> > > > > > bq.  Basically, one core had data in it that should belong to
> another
> > > > > > core. Here's my question about this: Is it possible that two
> request to
> > > > > the
> > > > > > /get API coming in at the same time would get confused and
> either both
> > > > > get
> > > > > > the same result or result get inverted?
> > > > > >
> > > > > > Well, that shouldn't be happening, these are all supposed to
be
> > > > > thread-safe
> > > > > > calls.... All things are possible of course ;)
> > > > > >
> > > > > > If two replicas of the same shard have different documents,
that
> could
> > > > > account
> > > > > > for what you're seeing, meanwhile begging the question of why
> that is
> > > > > the case
> > > > > > since it should never be true for a quiescent index. Technically
> there
> > > > > _are_
> > > > > > conditions where this is true on a very temporary basis, commits
> on the
> > > > > leader
> > > > > > and follower can trigger at different wall-clock times. Say
your
> soft
> > > > > commit
> > > > > > (or hard-commit-with-opensearcher-true) is 10 seconds. It should
> never
> > > > > be the
> > > > > > case that s1r1 and s1r2 are out of sync 10 seconds after the
> last update
> > > > > was
> > > > > > sent. This doesn't seem likely from what you've described
> though...
> > > > > >
> > > > > > Hmmmm. I guess that one other thing I can set up is to have
a
> bunch of
> > > > > dummy
> > > > > > collections laying around. Currently I have only the active
one,
> and
> > > > > > if there's some
> > > > > > code path whereby the RTG request goes to a replica of a
> different
> > > > > > collection, my
> > > > > > test setup wouldn't reproduce it.
> > > > > >
> > > > > > Currently, I'm running a 2-shard, 1 replica setup, so if there's
> some
> > > > > > way that the replicas
> > > > > > get out of sync that wouldn't show either.
> > > > > >
> > > > > > So I'm starting another run with these changes:
> > > > > > > opening a new connection each query
> > > > > > > switched so the collection I'm querying is 2x2
> > > > > > > added some dummy collections that are empty
> > > > > >
> > > > > > One nit, while "core" is exactly correct. When we talk about
a
> core
> > > > > > that's part of a collection, we try to use "replica" to be clear
> we're
> > > > > > talking about
> > > > > > a core with some added characteristics, i.e. we're in
> SolrCloud-land.
> > > > > > No big deal
> > > > > > of course....
> > > > > >
> > > > > > Best,
> > > > > > Erick
> > > > > > On Sat, Sep 29, 2018 at 8:28 AM Shawn Heisey <
> apache@elyograg.org>
> > > > > wrote:
> > > > > > >
> > > > > > > On 9/28/2018 8:11 PM, sgaron cse wrote:
> > > > > > > > @Shawn
> > > > > > > > We're running two instance on one machine for two
reason:
> > > > > > > > 1. The box has plenty of resources (48 cores / 256GB
ram)
> and since
> > > > > I was
> > > > > > > > reading that it's not recommended to use more than
31GB of
> heap in
> > > > > SOLR we
> > > > > > > > figured 96 GB for keeping index data in OS cache +
31 GB of
> heap per
> > > > > > > > instance was a good idea.
> > > > > > >
> > > > > > > Do you know that these Solr instances actually DO need
31 GB
> of heap,
> > > > > or
> > > > > > > are you following advice from somewhere, saying "use one
> quarter of
> > > > > your
> > > > > > > memory as the heap size"?  That advice is not in the Solr
> > > > > documentation,
> > > > > > > and never will be.  Figuring out the right heap size requires
> > > > > > > experimentation.
> > > > > > >
> > > > > > >
> > > > >
> https://wiki.apache.org/solr/SolrPerformanceProblems#How_much_heap_space_do_I_need.3F
> > > > > > >
> > > > > > > How big (on disk) are each of these nine cores, and how
many
> documents
> > > > > > > are in each one?  Which of them is in each Solr instance?
> With that
> > > > > > > information, we can make a *guess* about how big your heap
> should be.
> > > > > > > Figuring out whether the guess is correct generally requires
> careful
> > > > > > > analysis of a GC log.
> > > > > > >
> > > > > > > > 2. We're in testing phase so we wanted a SOLR cloud
> configuration,
> > > > > we will
> > > > > > > > most likely have a much bigger deployment once going
to
> production.
> > > > > In prod
> > > > > > > > right now, we currently to run a six machines Riak
cluster.
> Riak is a
> > > > > > > > key/value document store an has SOLR built-in for
search,
> but we are
> > > > > trying
> > > > > > > > to push the key/value aspect of Riak inside SOLR.
That way
> we would
> > > > > have
> > > > > > > > one less piece to worry about in our system.
> > > > > > >
> > > > > > > Solr is not a database.  It is not intended to be a data
> repository.
> > > > > > > All of its optimizations (most of which are actually in
> Lucene) are
> > > > > > > geared towards search.  While technically it can be a
> key-value store,
> > > > > > > that is not what it was MADE for.  Software actually designed
> for that
> > > > > > > role is going to be much better than Solr as a key-value
store.
> > > > > > >
> > > > > > > > When I say null document, I mean the /get API returns:
{doc:
> null}
> > > > > > > >
> > > > > > > > The problem is definitely not always there. We also
have
> large
> > > > > period of
> > > > > > > > time (few hours) were we have no problems. I'm just
extremely
> > > > > hesitant on
> > > > > > > > retrying when I get a null document because in some
case,
> getting a
> > > > > null
> > > > > > > > document is a valid outcome. Our caching layer heavily
rely
> on this
> > > > > for
> > > > > > > > example. If I was to retry every nulls I'd pay a big
penalty
> in
> > > > > > > > performance.
> > > > > > >
> > > > > > > I've just done a little test with the 7.5.0 techproducts
> example.  It
> > > > > > > looks like returning doc:null actually is how the RTG handler
> says it
> > > > > > > didn't find the document.  This seems very wrong to me,
but I
> didn't
> > > > > > > design it, and that response needs SOME kind of format.
> > > > > > >
> > > > > > > Have you done any testing to see whether the standard
> searching handler
> > > > > > > (typically /select, but many other URL paths are possible)
> returns
> > > > > > > results when RTG doesn't?  Do you know for these failures
> whether the
> > > > > > > document has been committed or not?
> > > > > > >
> > > > > > > > As for your last comment, part of our testing phase
is also
> testing
> > > > > the
> > > > > > > > limits. Our framework has auto-scaling built-in so
if we
> have a
> > > > > burst of
> > > > > > > > request, the system will automatically spin up more
clients.
> We're
> > > > > pushing
> > > > > > > > 10% of our production system to that Test server to
see how
> it will
> > > > > handle
> > > > > > > > it.
> > > > > > >
> > > > > > > To spin up another replica, Solr must copy all its index
data
> from the
> > > > > > > leader replica.  Not only can this take a long time if
the
> index is
> > > > > big,
> > > > > > > but it will put a lot of extra I/O load on the machine(s)
with
> the
> > > > > > > leader roles.  So performance will actually be WORSE before
it
> gets
> > > > > > > better when you spin up another replica, and if the index
is
> big, that
> > > > > > > condition will persist for quite a while.  Copying the
index
> data will
> > > > > > > be constrained by the speed of your network and by the
speed
> of your
> > > > > > > disks.  Often the disks are slower than the network, but
that
> is not
> > > > > > > always the case.
> > > > > > >
> > > > > > > Thanks,
> > > > > > > Shawn
> > > > > > >
> > > > >
>

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