Re: performance problem on big tables

Hi Daniel,
I already tried to set the destination table to unlogged - it improved the
performance slightly. Is there a way to make sure that I/O is the problem ?

2017-08-17 0:46 GMT+03:00 Daniel Blanch Bataller <
daniel(dot)blanch(dot)bataller(at)gmail(dot)com>:

> Seems your disks are too slow. On my laptop (nothing special, just one
> disk) using COPY I can dump 3G in ~ 20 secs, loading takes 120 secs, bare
> copying 3G takes 10 secs.
>
> Similar proportion you had, but much faster.
>
> confirm I/O is your bottleneck, and tell us how you solved your problem
>
> Anyway, You can cut import time by half if you set your destination table
> to unlogged (postgres will write half the data, it will save the
> transaction log writing). Remember to set it to logged when finished!!
>
>
> Regards,
>
> Daniel
>
> El 16 ago 2017, a las 16:32, Mariel Cherkassky <
> mariel(dot)cherkassky(at)gmail(dot)com> escribió:
>
> My server is virtual and it have virtual hd from a vnx storage machine.
> The logs and the data are on the same disk.
>
> 2017-08-16 17:04 GMT+03:00 Daniel Blanch Bataller <
> daniel(dot)blanch(dot)bataller(at)gmail(dot)com>:
>
>> Considering it has to write logs and data at checkpoints I don’t see it
>> particularly slow compared to the extract phase. What kind of disks you
>> have SSD or regular disks? Different disks for ltransaction logs and data?
>>
>>
>> El 16 ago 2017, a las 15:54, Mariel Cherkassky <
>> mariel(dot)cherkassky(at)gmail(dot)com> escribió:
>>
>> I run the copy command via psql to create a local dump of a 3G table and
>> it took me 134059.732ms =~2 minutes. After that I imported the data via
>> copy and it took 458648.677ms =~7 minutes. So the copy command works but
>> pretty slow.
>>
>> 2017-08-16 16:08 GMT+03:00 Daniel Blanch Bataller <
>> daniel(dot)blanch(dot)bataller(at)gmail(dot)com>:
>>
>>> See if the copy command is actually working, copy should be very fast
>>> from your local disk.
>>>
>>>
>>> El 16 ago 2017, a las 14:26, Mariel Cherkassky <
>>> mariel(dot)cherkassky(at)gmail(dot)com> escribió:
>>>
>>>
>>> After all the changes of the memory parameters the same
>>> operation(without the copy utility) didnt run much faster - it took one
>>> minute less. I made a test with the copy command (without the 'with
>>> binary') and it took 1.5 hours to create the dumpfile in my local
>>> postgresql server. Then I tried to run the copy from the local dump and it
>>> is already running two hours and it didnt even finish. I looked at the
>>> server log and I saw that I run the copy command at 13:18:05, 3 minutes
>>> later checkpoint started and completed and there are no messages in the log
>>> after that. What can I do ? Improving the memory parameters and the memory
>>> on the server didnt help and for now the copy command doesnt help either.
>>>
>>>
>>>
>>>
>>> 2017-08-15 20:14 GMT+03:00 Scott Marlowe <scott(dot)marlowe(at)gmail(dot)com>:
>>>
>>>> On Tue, Aug 15, 2017 at 4:06 AM, Mariel Cherkassky
>>>> <mariel(dot)cherkassky(at)gmail(dot)com> wrote:
>>>> > Hi,
>>>> > So I I run the cheks that jeff mentioned :
>>>> > \copy (select * from oracle_remote_table) to /tmp/tmp with binary - 1
>>>> hour
>>>> > and 35 minutes
>>>>
>>>> So 26G takes 95 minutes, or 27 MB/minute or 456k/second? Sound about
>>>> right (it's early, I haven't had enough coffee please check my math).
>>>> That's pretty slow unless you're working across pretty big distances
>>>> with mediocre connections. My home internet downloads about 100MB/s
>>>> by comparison.
>>>>
>>>> > \copy local_postresql_table from /tmp/tmp with binary - Didnt run
>>>> because
>>>> > the remote oracle database is currently under maintenance work.
>>>>
>>>> You shouldn't need the remote oracle server if you've already copied
>>>> it over, you're just copying from local disk into the local pgsql db.
>>>> Unless I'm missing something.
>>>>
>>>> > So I decided to follow MichaelDBA tips and I set the ram on my
>>>> machine to
>>>> > 16G and I configured the effective_cache memory to 14G,tshared_buffer
>>>> to be
>>>> > 2G and maintenance_work_mem to 4G.
>>>>
>>>> Good settings. Maybe set work_mem to 128MB or so while you're at it.
>>>>
>>>> > I started running the copy checks again and for now it coppied 5G in
>>>> 10
>>>> > minutes. I have some questions :
>>>> > 1)When I run insert into local_postresql_table select * from
>>>> > remote_oracle_table I insert that data as bulk to the local table or
>>>> row by
>>>> > row ? If the answer as bulk than why copy is a better option for
>>>> this case
>>>> > ?
>>>>
>>>> insert into select from oracle remote is one big copy, but it will
>>>> take at least as long as copying from oracle to the local network
>>>> took. Compare that to the same thing but use file_fdw on the file
>>>> locally.
>>>>
>>>> > 2)The copy from dump into the postgresql database should take less
>>>> time than
>>>> > the copy to dump ?
>>>>
>>>> Yes. The copy from Oracle to your local drive is painfully slow for a
>>>> modern network connection.
>>>>
>>>> > 3)What do you think about the new memory parameters that I cofigured ?
>>>>
>>>> They should be OK. I'm more worried about the performance of the io
>>>> subsystem tbh.
>>>>
>>>
>>>
>>>
>>
>>
>
>