Re: Re: Server side cursor limitations for on demand loading of data in query tool [RM2137] [pgAdmin4]

Hi Harshal!

We applied your patch and ran the Javascript tests and realized there are 6
tests failing. After that we replicate the failures by hand and found the
following issues:

- Clicking in the checkboxes of the rows does not select the row anymore.
- When copying and pasting (any) data, we realized that it copied an empty
dataset.

We didn't review the patch further because there aren't any tests for the
newly implemented functionality.

Is there a place to find a dataset with 96k rows that you guys were testing
with?

Note: To run the Javascript test you can use the following commands
```
$ cd web
$ yarn install
$ yarn run karma start --single-run
```

Thanks
Joao & Sarah

On Mon, May 8, 2017 at 9:16 AM, Harshal Dhumal <
harshal(dot)dhumal(at)enterprisedb(dot)com> wrote:

> Hi Dave,
>
> --
> *Harshal Dhumal*
> *Sr. Software Engineer*
>
> EnterpriseDB India: http://www.enterprisedb.com
> The Enterprise PostgreSQL Company
>
> On Mon, May 8, 2017 at 4:49 PM, Dave Page <dpage(at)pgadmin(dot)org> wrote:
>
>> Hi
>>
>> This is fantastic! The speedup in the query tool is phenomenal with large
>> result sets. For 96K rows, I'm now seeing 1 second until I can browse the
>> data, vs. 13 in v1.4 (and 22 secs in pgAdmin 3)!! Awesome work Harshal :-)
>>
>> Questions/comments:
>>
>> - Can we put the row number in the left-hand column, to the right of the
>> checkbox? This patch highlights just how much value that had in pgAdmin 3
>> (I hadn't realised we had missed it until now)
>>
>> - If the user clicks the checkbox to select all rows, we need to retrieve
>> them all at that time, otherwise they may be inadvertently working with a
>> truncated result set.
>>
>> Sure I'll do above both the changes.
>
>
>> - Are any changes needed to ensure the Download button works? I'm seeing
>> missing rows in my test here, but that could be because of the known issues
>> there with Unicode.
>>
>> This is fixed and checked in.
>
>
>
>> Thanks!
>>
>>
>> On Sun, May 7, 2017 at 6:10 PM, Harshal Dhumal <
>> harshal(dot)dhumal(at)enterprisedb(dot)com> wrote:
>>
>>> Hi,
>>>
>>> Here is patch for initial implementation of on demand loading of result
>>> set for query tool and datagrid.
>>>
>>> --
>>> *Harshal Dhumal*
>>> *Sr. Software Engineer*
>>>
>>> EnterpriseDB India: http://www.enterprisedb.com
>>> The Enterprise PostgreSQL Company
>>>
>>> On Tue, Apr 25, 2017 at 5:21 PM, Dave Page <dpage(at)pgadmin(dot)org> wrote:
>>>
>>>> Hi
>>>>
>>>> On Tue, Apr 25, 2017 at 8:41 AM, Harshal Dhumal <
>>>> harshal(dot)dhumal(at)enterprisedb(dot)com> wrote:
>>>>
>>>>> Hi Dave,
>>>>>
>>>>> To implement feature #2137
>>>>> <https://redmine.postgresql.org/issues/2137> we'll need to use server
>>>>> cursor. However server cursor has some
>>>>> limitation.
>>>>> For eg.
>>>>> 1. It cannot execute BEGIN; query (basically user cannot start new
>>>>> database transaction)
>>>>> 2. In case if Auto commit is true then we try to execute user queries
>>>>> inside BEGIN and END when ever it's possible even though user has not put
>>>>> BEGIN and END in his query.
>>>>>
>>>>> Also not all queries executed using Query tool produces records as
>>>>> result. So can we assume only
>>>>> queries started with SELECT should be executed using server cursor to
>>>>> support on demand loading.
>>>>> Or should we give user an option to use on demand loading like we have
>>>>> options for Auto commit? and Auto rollback?
>>>>> In case of on demand loading option user will be responsible to
>>>>> execute correct queries (queries which can be executed using server cursor)
>>>>>
>>>>> Let me know your opinion on this.
>>>>>
>>>>
>>>> Hmm, those are good points.
>>>>
>>>> So, as a first step, there's no absolute requirement to use a server
>>>> side cursor here. The results can be materialised in libpq/psycopg2
>>>> (perhaps using an async query), then transferred to the client in batches
>>>> as described in the ticket.
>>>>
>>>> I think this would be a significant improvemet - we can re-visit the
>>>> possibility of using server side cursors in the future when we have more
>>>> ability to parse the query string before executing it (something we will
>>>> want to do when we merge query tool/edit grid functionality).
>>>>
>>>> --
>>>> Dave Page
>>>> Blog: http://pgsnake.blogspot.com
>>>> Twitter: @pgsnake
>>>>
>>>> EnterpriseDB UK: http://www.enterprisedb.com
>>>> The Enterprise PostgreSQL Company
>>>>
>>>
>>>
>>
>>
>> --
>> Dave Page
>> Blog: http://pgsnake.blogspot.com
>> Twitter: @pgsnake
>>
>> EnterpriseDB UK: http://www.enterprisedb.com
>> The Enterprise PostgreSQL Company
>>
>
>