Re: Jira Doc Access

[David Mollitor]

Thanks Ashutosh!

On Mon, Apr 13, 2020 at 12:27 PM Ashutosh Chauhan 
wrote:

> Hi David,
> Added you to Hive wiki.
> Thanks,
> Ashutosh
>
> On Mon, Apr 13, 2020 at 6:39 AM David Mollitor  wrote:
>
>> Hello Team,
>>
>> Is anyone able to grant me access to the Apache Hive Wiki (dmollitor) ?
>>
>> Also, is there any discussion/interest in moving docs into the git repo?
>>
>> Thanks!
>>
>

Jira Doc Access

[David Mollitor]

Hello Team,

Is anyone able to grant me access to the Apache Hive Wiki (dmollitor) ?

Also, is there any discussion/interest in moving docs into the git repo?

Thanks!

Re: Query Failures

[David Mollitor]

https://community.cloudera.com/t5/Support-Questions/Map-and-Reduce-Error-Java-heap-space/td-p/45874

On Fri, Feb 14, 2020, 6:58 PM David Mollitor  wrote:

> Hive has many optimizations.  One is that it will load the data directly
> from storage (HDFS) if it's a trivial query.  For example:
>
> Select * from table limit 10;
>
> In natural language it says "give me any ten rows (if available) from the
> table."  You don't need the overhead of launching a full mapreduce job for
> this.  Just read the rows from the file directly.
>
> Adding additional predicates on the query requires a mapreduce job to do
> the heavy lifting.  The error message you're getting is probably the result
> of a failed mapreduce job.  Nine times out of ten, the problem is that the
> mappers/reducers are not granted enough memory for their YARN containers.
>
> On Tue, Feb 11, 2020, 10:41 AM Pau Tallada  wrote:
>
>> Hi,
>>
>> Do you have more complete tracebacks?
>>
>> Missatge de Charles Givre  del dia dt., 11 de febr.
>> 2020 a les 2:54:
>>
>>> Hello Everyone!
>>> I recently joined a project that has a Hive/Impala installation and we
>>> are experience a significant number of query failures.  We are using an
>>> older version of Hive, and unfortunately there's nothing iI can do about
>>> that, but I'm wondering is how I can make Hive do better with queries to
>>> give our users a better experience.
>>>
>>> For example, I can execute a basic SELECT * query or SELECT 
>>> query without issues.
>>>
>>> However, if I attempt to:
>>> 1.  Add filters
>>> 2.  Do a SELECT DISTINCT
>>> 3.  Perform basic aggregation
>>>
>>> I get errors like this: Execution Error, return code 1 from
>>> org.apache.hadoop.hive.ql.exec.mr.MapRedTask.
>>>
>>> Could someone point me to some good guides for querying Hive and/or
>>> assisting my engineers in preventing these errors?
>>> Thanks,
>>>
>>>
>>
>> --
>> --
>> Pau Tallada Crespí
>> Dep. d'Astrofísica i Cosmologia
>> Port d'Informació Científica (PIC)
>> Tel: +34 93 170 2729
>> --
>>
>>

Re: Query Failures

[David Mollitor]

Hive has many optimizations.  One is that it will load the data directly
from storage (HDFS) if it's a trivial query.  For example:

Select * from table limit 10;

In natural language it says "give me any ten rows (if available) from the
table."  You don't need the overhead of launching a full mapreduce job for
this.  Just read the rows from the file directly.

Adding additional predicates on the query requires a mapreduce job to do
the heavy lifting.  The error message you're getting is probably the result
of a failed mapreduce job.  Nine times out of ten, the problem is that the
mappers/reducers are not granted enough memory for their YARN containers.

On Tue, Feb 11, 2020, 10:41 AM Pau Tallada  wrote:

> Hi,
>
> Do you have more complete tracebacks?
>
> Missatge de Charles Givre  del dia dt., 11 de febr.
> 2020 a les 2:54:
>
>> Hello Everyone!
>> I recently joined a project that has a Hive/Impala installation and we
>> are experience a significant number of query failures.  We are using an
>> older version of Hive, and unfortunately there's nothing iI can do about
>> that, but I'm wondering is how I can make Hive do better with queries to
>> give our users a better experience.
>>
>> For example, I can execute a basic SELECT * query or SELECT 
>> query without issues.
>>
>> However, if I attempt to:
>> 1.  Add filters
>> 2.  Do a SELECT DISTINCT
>> 3.  Perform basic aggregation
>>
>> I get errors like this: Execution Error, return code 1 from
>> org.apache.hadoop.hive.ql.exec.mr.MapRedTask.
>>
>> Could someone point me to some good guides for querying Hive and/or
>> assisting my engineers in preventing these errors?
>> Thanks,
>>
>>
>
> --
> --
> Pau Tallada Crespí
> Dep. d'Astrofísica i Cosmologia
> Port d'Informació Científica (PIC)
> Tel: +34 93 170 2729
> --
>
>

Re: Why Hive uses MetaStore？

[David Mollitor]

In the beginning, hive was a command line tool.  All the heavy lifting
happened on the user's local box.  If a user wanted to execute hive from
their laptop, or a server, it always needs access to the list of available
tables (and their schemas and their locations), otherwise every SQL script
would have to start with the table definition of every table involved in
the query. Today, it's primarily HiveServer2 and there can be many
instances in the same environment.  They all need to share table meta data.

It is also helpful to keep statistics on every table.  Table statistics are
key in generating efficient query plans.  If yue statistics are not
persisted anywhere, it would be lost after every query.

Since Hive2, the role of the metastore has only expanded to include, for
example, a global locking system to protect tables from concurrent access.

On Wed, Jan 15, 2020, 9:51 AM qq <987626...@qq.com> wrote:

> Hello:
>   Why Hive uses MetaStore？Is there a related JIRA?
>
>  thinks.
>  I am looking forward to your reply！
>

Re: Alternatives to Streaming Mutation API in Hive 3.x

[David Mollitor]

Hello,

Streaming? NiFi

Upserts? HBase, Kudu, Hive 3.x

Doing upserts on Hive can be cumbersome, depending on the use case.  If
Upserts are being submitted continuously and quickly, it can overwhelm the
system because it will require a scan across the data set (for all intents
and purposes) for each query submission.

On Mon, Jan 13, 2020, 5:56 AM Nandakishore Mm 
wrote:

> Hi Hive Team,
> I have a use case where data has to be continuously streamed into a hive
> table as well as old records with the same primary key have to be
> updated/deleted (i.e. upserts). This document
> 
>  for
> 'HCatalog Streaming Mutation API' seems to be suitable for my use case but
> is deprecated from Hive 3 onwards. Is there any alternative for is feature
> or any other way to handle my use case with Hive?
>
> Thanks and Regards,
> Nandakishore MM
> Software Developer
> Flipkart
> Mobile : +91 9043412922
>
>
> --
> Nandakishore MM
> Mobile : +91 9043412922
>
>
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Re: What is the Hive HA processing mechanism?

[David Mollitor]

Hello,

Not sure if this answers your question, but please note the following:

Processing occurs via MapReduce, Spark, or Tez.  The processing engines run
on top of YARN.  Each processing engine derives much of their HA from
YARN.  There are some quarks there, but these engines running on YARN is
generally considered to be highly available.

HiveServer2 does not share client session state between instances.
Therefore, if a single HiveServer2 instance is lost, all of the work being
performed which was originated from this instance will be lost.  Clients
will have to re-connect to another instance of HiveServer2 and re-submit
their queries.  There is no transparent client fail-over offered at this
time.

Thanks.

On Fri, Nov 15, 2019 at 2:05 AM qq <987626...@qq.com> wrote:

> Hello:
>
>   What is the Hive HA processing mechanism? What problems can be
> solved?
>
> thinks.
> I am looking forward to your reply！
>