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### Author:  [@dadoonet](https://discuss.elastic.co/u/dadoonet)
#### Post date: [December 14, 2014, 9:13am UTC](https://discuss.elastic.co/t/looking-for-a-best-practice-to-get-all-data-according-to-some-filters/21195/8 "2014-12-14T09:13:08Z")
Implication is the memory needed to be allocated on each shard.
David
> Le 14 déc. 2014 à 05:46, Ron Sher [ron.sher@gmail.com](mailto:ron.sher@gmail.com) a écrit :
>
> Again, why not use a very large count size? What are the implications of using a very large count?
> Regarding performance - it seems doing 1 request with a very large count performs better than using scan scroll (with count of 100 using 32 shards)
>
> > On Wednesday, December 10, 2014 10:53:50 PM UTC+2, David Pilato wrote:
> > No I did not say that. Or I did not mean that. Sorry if it was unclear.
> > I said: don’t use large sizes:
> >
> > > > Never use size:10000000 or from:10000000.
> >
> > You should read this: [Elasticsearch Platform — Find real-time answers at scale | Elastic](http://www.elasticsearch.org/guide/en/elasticsearch/reference/current/search-request-scroll.html#scroll-scan)
> >
> > --
> > David Pilato | Technical Advocate | [Elasticsearch.com](http://Elasticsearch.com)
> > @dadoonet | @elasticsearchfr | @scrutmydocs
> >
> > > Le 10 déc. 2014 à 21:16, Ron Sher [ron....@gmail.com](mailto:ron....@gmail.com) a écrit :
> > >
> > > So you're saying there's no impact on elasticsearch if I issue a large size?
> > > If that's the case then why shouldn't I just call size of 1M if I want to make sure I get everything?
> > >
> > > > On Wednesday, December 10, 2014 8:22:47 PM UTC+2, David Pilato wrote:
> > > > Scan/scroll is the best option to extract a huge amount of data.
> > > > Never use size:10000000 or from:10000000.
> > > >
> > > > It's not realtime because you basically scroll over a given set of segments and all new changes that will come in new segments won't be taken into account during the scroll.
> > > > Which is good because you won't get inconsistent results.
> > > >
> > > > About size, I'd would try and test. It depends on your docs size I believe.
> > > > Try with 10000 and see how it goes when you increase it. You will may be discover that getting 10_10000 docs is the same as 1_100000. 🙂
> > > >
> > > > Best
> > > >
> > > > David
> > > >
> > > > > Le 10 déc. 2014 à 19:09, Ron Sher [ron....@gmail.com](mailto:ron....@gmail.com) a écrit :
> > > > >
> > > > > Hi,
> > > > >
> > > > > I was wondering about best practices to to get all data according to some filters.
> > > > > The options as I see them are:
> > > > > Use a very big size that will return all accounts, i.e. use some value like 1m to make sure I get everything back (even if I need just a few hundreds or tens of documents). This is the quickest way, development wise.
> > > > > Use paging - using size and from. This requires looping over the result and the performance gets worse as we advance to later pages. Also, we need to use preference if we want to get consistent results over the pages. Also, it's not clear what's the recommended size for each page.
> > > > > Use scan/scroll - this gives consistent paging but also has several drawbacks: If I use search\_type=scan then it can't be sorted; using scan/scroll is (maybe) less performant than paging (the documentation says it's not for realtime use); again not clear which size is recommended.
> > > > > So you see - many options and not clear which path to take.
> > > > >
> > > > > What do you think?
> > > > >
> > > > > Thanks,
> > > > > Ron
> > > > >
> > > > > --
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### Author:  [@nik9000](https://discuss.elastic.co/u/nik9000)
#### Post date: [December 14, 2014, 2:58pm UTC](https://discuss.elastic.co/t/looking-for-a-best-practice-to-get-all-data-according-to-some-filters/21195/9 "2014-12-14T14:58:27Z")
Search consumes O(offset + size) memory and O(ln(offset +
size)\*(offset+size) CPU. Scan scroll has higher overhead but is O(size) the
whole time. I don't know the break even point.
The other thing is that scroll provides a consistent snapshot. That means
it consumes resources you shouldn't let end users expose but it won't miss
results or have repeats like scrolling with increasing offset.
You can certainly do large fetches with big size but its less stable in
general.
Finally, scan/scroll has always been pretty quick for me. I usually use a
batch size in the thousands.
Nik
On Dec 14, 2014 4:13 AM, "David Pilato" [david@pilato.fr](mailto:david@pilato.fr) wrote:
> Implication is the memory needed to be allocated on each shard.
>
> David
>
> Le 14 déc. 2014 à 05:46, Ron Sher [ron.sher@gmail.com](mailto:ron.sher@gmail.com) a écrit :
>
> Again, why not use a very large count size? What are the implications of
> using a very large count?
> Regarding performance - it seems doing 1 request with a very large count
> performs better than using scan scroll (with count of 100 using 32 shards)
>
> On Wednesday, December 10, 2014 10:53:50 PM UTC+2, David Pilato wrote:
>
> > No I did not say that. Or I did not mean that. Sorry if it was unclear.
> > I said: don’t use large sizes:
> >
> > Never use size:10000000 or from:10000000.
> >
> > >
> >
> > You should read this: [Elasticsearch Platform — Find real-time answers at scale | Elastic](http://www.elasticsearch.org/guide/en/)
> > elasticsearch/reference/current/search-request-scroll.html#scroll-scan
> >
> > --
> > _David Pilato_ | _Technical Advocate_ | _[Elasticsearch.com](http://Elasticsearch.com)
> > [http://Elasticsearch.com](http://Elasticsearch.com)_
> > @dadoonet [https://twitter.com/dadoonet](https://twitter.com/dadoonet) | @elasticsearchfr
> > [https://twitter.com/elasticsearchfr](https://twitter.com/elasticsearchfr) | @scrutmydocs
> > [https://twitter.com/scrutmydocs](https://twitter.com/scrutmydocs)
> >
> > Le 10 déc. 2014 à 21:16, Ron Sher [ron....@gmail.com](mailto:ron....@gmail.com) a écrit :
> >
> > So you're saying there's no impact on elasticsearch if I issue a large
> > size?
> > If that's the case then why shouldn't I just call size of 1M if I want to
> > make sure I get everything?
> >
> > On Wednesday, December 10, 2014 8:22:47 PM UTC+2, David Pilato wrote:
> >
> > > Scan/scroll is the best option to extract a huge amount of data.
> > > Never use size:10000000 or from:10000000.
> > >
> > > It's not realtime because you basically scroll over a given set of
> > > segments and all new changes that will come in new segments won't be taken
> > > into account during the scroll.
> > > Which is good because you won't get inconsistent results.
> > >
> > > About size, I'd would try and test. It depends on your docs size I
> > > believe.
> > > Try with 10000 and see how it goes when you increase it. You will may be
> > > discover that getting 10_10000 docs is the same as 1_100000. 🙂
> > >
> > > Best
> > >
> > > David
> > >
> > > Le 10 déc. 2014 à 19:09, Ron Sher [ron....@gmail.com](mailto:ron....@gmail.com) a écrit :
> > >
> > > Hi,
> > >
> > > I was wondering about best practices to to get all data according to
> > > some filters.
> > > The options as I see them are:
> > >
> > > - Use a very big size that will return all accounts, i.e. use some
> > > value like 1m to make sure I get everything back (even if I need just a few
> > > hundreds or tens of documents). This is the quickest way, development wise.
> > > - Use paging - using size and from. This requires looping over the
> > > result and the performance gets worse as we advance to later pages. Also,
> > > we need to use preference if we want to get consistent results over the
> > > pages. Also, it's not clear what's the recommended size for each page.
> > > - Use scan/scroll - this gives consistent paging but also has
> > > several drawbacks: If I use search\_type=scan then it can't be sorted; using
> > > scan/scroll is (maybe) less performant than paging (the documentation says
> > > it's not for realtime use); again not clear which size is recommended.
> > >
> > > So you see - many options and not clear which path to take.
> > >
> > > What do you think?
> > >
> > > Thanks,
> > > Ron
> > >
> > > --
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### Author:  [@Jonathan\_Foy](https://discuss.elastic.co/u/Jonathan_Foy)
#### Post date: [December 14, 2014, 5:47pm UTC](https://discuss.elastic.co/t/looking-for-a-best-practice-to-get-all-data-according-to-some-filters/21195/10 "2014-12-14T17:47:17Z")
Just to reword what others have said, ES will allocate memory for [size] scores as I understand it (per shard?) regardless of the final result count. If you're getting back 4986 results from a query, it'd be faster to use "size": 4986 than "size": 1000000.
What I've done in similar situations is to issue a count first with the same filter (which is very fast), then use the result of that in the size field. It worked much better/faster than using a default large size.
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### Author:  [@system](https://discuss.elastic.co/u/system)
#### Post date: [July 6, 2017, 12:43am UTC](https://discuss.elastic.co/t/looking-for-a-best-practice-to-get-all-data-according-to-some-filters/21195/11 "2017-07-06T00:43:47Z")