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From Emir Arnautović <emir.arnauto...@sematext.com>
Subject Re: questions regrading stored fields role in query time
Date Tue, 26 Feb 2019 10:40:56 GMT
Hi Saurabh,
DocValues can be used for retrieving field values (note that order will not be preserved in
case of multivalue field) but they are also stored in files, just different structures. Doc
values will load some structure in memory, but will also use memory mapped files to access
values (not familiar with this code and just assuming) so in any case it will use “shared”
OS caches. Those caches will be affected when loading stored fields to do partial update.
Also it’ll take some memory when indexing documents. That is why storing and doing partial
updates could indirectly affect query performances. But that might be insignificant and only
test can tell for sure. Unless you have small index and enough RAM, then I can also tell that
for sure.

Emir
--
Monitoring - Log Management - Alerting - Anomaly Detection
Solr & Elasticsearch Consulting Support Training - http://sematext.com/



> On 26 Feb 2019, at 11:21, Saurabh Sharma <saurabh.infoedge@gmail.com> wrote:
> 
> Hi Emir,
> 
> I had this question in my mind if I store my only returnable field as
> docValue in RAM.will my stored documents be referenced while constructing
> the response after the query. Ideally, as the field asked to return i.e fl
> is already in RAM then documents on disk should not be consulted for this
> field.
> 
> Any insight about the usage of docValued field vs stored field and
> preference order will help here in understanding the situation in a better
> way.
> 
> Thanks
> Saurabh
> 
> On Tue, Feb 26, 2019 at 2:41 PM Emir Arnautović <
> emir.arnautovic@sematext.com> wrote:
> 
>> Hi Saurabh,
>> Welcome to the channel!
>> Storing fields should not affect query performances directly if you use
>> lazy field loading and it is the default set. And it should not affect at
>> all if you have enough RAM compared to index size. Otherwise OS caches
>> might be affected by stored fields. The best way to tell is to tests with
>> expected indexing/partial updates load and see if/how much it affects
>> performances.
>> 
>> HTH,
>> Emir
>> --
>> Monitoring - Log Management - Alerting - Anomaly Detection
>> Solr & Elasticsearch Consulting Support Training - http://sematext.com/
>> 
>> 
>> 
>>> On 26 Feb 2019, at 09:34, Saurabh Sharma <saurabh.infoedge@gmail.com>
>> wrote:
>>> 
>>> Hi All ,
>>> 
>>> 
>>> I am new here on this channel.
>>> Few days back we upgraded our solr cloud to version 7.3 and doing
>> real-time
>>> document posting with 15 seconds soft commit and 2 minutes hard commit
>>> time.As of now we posting full document to solr which includes data
>>> accumulations from various sources.
>>> 
>>> Now we want to do partial updates.I went through the documentation and
>>> found that all the fields should be stored or docValues for partial
>>> updates. I have few questions regarding this?
>>> 
>>> 1) In case i am just fetching only 1 field while making query.What will
>> the
>>> performance impact due to all fields being stored? Lets say i have an
>> "id"
>>> field and i do have doc value true for the field, will solr use stored
>>> fields in this case? will it load whole document in RAM ?
>>> 
>>> 2)What's the impact of large stored fields (.fdt) on query time
>>> performance. Do query time even depend on the stored field or they just
>>> depend on indexes?
>>> 
>>> 
>>> Thanks and regards
>>> Saurabh
>> 
>> 


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