[pgadmin-hackers] Re: Server side cursor limitations for on demand loading of data inquery tool [RM2137] [pgAdmin4]

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.

- 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.

Thanks!

On Sun, May 7, 2017 at 6:10 PM, Harshal Dhumal <harshal.dhumal@enterprisedb.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@pgadmin.org> wrote:

Hi

On Tue, Apr 25, 2017 at 8:41 AM, Harshal Dhumal <harshal.dhumal@enterprisedb.com> wrote:

Hi Dave,

To implement feature #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