Обсуждение: PostgreSQL Portable

I just started to look at PostgreSQL to implement a large GIS DB (1Tb).  The data must reside in an external disk with eSATA connection and may be moved to different locations (and Windows desktops/laptops). I was looking to install PostgreSQL and PostGIS extensions on each PC (setting-up the proper PGDATA directory to the external disk) until I read about PostgreSQL and PgAdmin Portable …

 

http://sourceforge.net/projects/pgadminportable/

http://sourceforge.net/projects/postgresqlportable/

 

Is that a viable alternative considering the expected size of the DB? Any comments or proposal would be appreciated J

a 1TB database on a single disk drive, presumably 7200rpm, will not perform very well under any sort of concurrency, or doing any sort of operation that requires aggregating a lot of rows.

also, Windows disables writeback caching on external disks, this will greatly slow down update transactions.

-- 
john r pierce                                      37N 122W
somewhere on the middle of the left coast

On Sep 10, 2014, at 2:00 PM, Daniel Begin <jfd553@hotmail.com> wrote:

> First, I am a Newbie regarding PostgreSQL …
>
> I just started to look at PostgreSQL to implement a large GIS DB (1Tb).  The data must reside in an external disk
witheSATA connection and may be moved to different locations (and Windows desktops/laptops). I was looking to install
PostgreSQLand PostGIS extensions on each PC (setting-up the proper PGDATA directory to the external disk) until I read
aboutPostgreSQL and PgAdmin Portable … 
>
> http://sourceforge.net/projects/pgadminportable/
> http://sourceforge.net/projects/postgresqlportable/


>  Is that a viable alternative considering the expected size of the DB? Any comments or proposal would be appreciated
.

Adding postgis to that, if it's not already included, might take some work. Not impossible but you'd be making some
unneededwork for yourself. 

The external disk isn't going to be blindingly fast, however you use it. For Windows in particular, it's probably going
tobe more conservative in caching the external drive than it would an internal one. Any large or unindexed queries are
likelyto be a bit painful. 

I do use an external drive for some work, though, and it's usable. I have all of postgresql and the tools I use
installedon the drive, with nothing for that instance installed on my laptop. I just have the external drives bin
directoryearly in my PATH, so I can plug in the drive and do pg_ctl start, and it all works. That's on a mac, I'm sure
youcould do the same with Windows. 

Cheers,
  Steve

First, I am a Newbie regarding PostgreSQL …

 

I just started to look at PostgreSQL to implement a large GIS DB (1Tb).  The data must reside in an external disk with eSATA connection and may be moved to different locations (and Windows desktops/laptops). I was looking to install PostgreSQL and PostGIS extensions on each PC (setting-up the proper PGDATA directory to the external disk) until I read about PostgreSQL and PgAdmin Portable …

 

http://sourceforge.net/projects/pgadminportable/

http://sourceforge.net/projects/postgresqlportable/

 

Is that a viable alternative considering the expected size of the DB? Any comments or proposal would be appreciated J

Daniel

It appears you are looking to take the PostgreSQL data directory from machine to machine on an external drive. I fear you will run into some potential problems:

1. Performance (mentioned by others).

2. OS mismatch. Have you ensured that all client machines are running identical setups? The underlying files are not guaranteed portable between OS versions and 64/32-bit. In fact they probably won't be.

3. Backups. What happens when one user screws up the database?

Perhaps you could explain further the genesis of this requirement. The message list is littered with questions like this asking how to implement a certain solution when, given an understanding of the reason the question is being asked, a far better solution exists. This happens even more often when the person asking is a "newbie."

Cheers,
Steve

On Thu, Sep 11, 2014 at 08:40:21AM +0200, Rémi Cura wrote:

> It is also easy to backup (but very slow due to huge iso file).

- rsync when you plug in
- make a copy
- rsync to copy continously during work
  (note that this rsynced copy will be inconsistent,
  it only serves to speed up the last step)
- final rsync to copy after you shut down the
  virtual machine before you unplug the external disk
- delete the initial rsync (which was the copy
  _before_ this session)

Should be acceptably fast even with large VMs.

Karsten
--
GPG key ID E4071346 @ gpg-keyserver.de
E167 67FD A291 2BEA 73BD  4537 78B9 A9F9 E407 1346

On Wed, 10 Sep 2014 14:19:45 -0700, John R Pierce
<pierce@hogranch.com> wrote:

>also, Windows disables writeback caching on external disks, this will
>greatly slow down update transactions.

Not exactly.  By default, write caching is disabled for external
drives to support quick disconnect, i.e. yanking the device without
unmounting it.

If the driver permits it and you [or your users] can be trusted to
perform a safe unmount via the OS *before* disconnecting the device,
then you can enable write caching for the device using the device
manager.  [Note that the device must be connected for it to be visible
in the device manager.]

Most USB disks and Flash devices do support write caching.  If you are
willing to live dangerously, you can get better write performance.

George

On 09/11/2014 05:50 AM, Steve Crawford wrote:
> 2. OS mismatch. Have you ensured that all client machines are running
> identical setups? The underlying files are not guaranteed portable
> between OS versions and 64/32-bit. In fact they probably won't be.

You can just run 32-bit Pg on both the 32-bit and 64-bit hosts without
problems.

--
 Craig Ringer                   http://www.2ndQuadrant.com/
 PostgreSQL Development, 24x7 Support, Training & Services

On 09/11/2014 03:16 PM, George Neuner wrote:
>
> If the driver permits it and you [or your users] can be trusted to
> perform a safe unmount via the OS *before* disconnecting the device,
> then you can enable write caching for the device using the device
> manager.  [Note that the device must be connected for it to be visible
> in the device manager.]

It shouldn't be living dangerously, actually.

While I haven't tested it myself, writeback caching on the external
drive should be safe so long as it continues to honour explicit disk
flush requests.

That's why we have the WAL and do periodic checkpoints. If you yank the
drive mid-write you'll lose uncommitted transactions and might have
slower startup next time around, but it should otherwise not be overly
problematic.

--
 Craig Ringer                   http://www.2ndQuadrant.com/
 PostgreSQL Development, 24x7 Support, Training & Services

Hi Craig,

On Fri, 12 Sep 2014 11:33:55 +0800, Craig Ringer
<craig@2ndquadrant.com> wrote:

>On 09/11/2014 03:16 PM, George Neuner wrote:
>>
>> If the driver permits it and you [or your users] can be trusted to
>> perform a safe unmount via the OS *before* disconnecting the device,
>> then you can enable write caching for the device using the device
>> manager.  [Note that the device must be connected for it to be visible
>> in the device manager.]
>
>It shouldn't be living dangerously, actually.
>
>While I haven't tested it myself, writeback caching on the external
>drive should be safe so long as it continues to honour explicit disk
>flush requests.
>
>That's why we have the WAL and do periodic checkpoints. If you yank the
>drive mid-write you'll lose uncommitted transactions and might have
>slower startup next time around, but it should otherwise not be overly
>problematic.

For the most part you're correct, but recall that WAL itself can be
made asynchronous [see fsync() and synchronous_commit() settings] and
the periodic OS sync also may be disabled - which doesn't affect WAL
handling but may(?) affect the background writer.

Even having synchronous WAL the most recent transactions can be lost
if the log device fails *during* a write.  That's why, if we use
external devices at all, we tend to use closely coupled devices - disk
array, wired SAN, etc. - that aren't very likely to be physically
disconnected.  And uninterruptible power all around 8-)

A portable device can be reasonably safe if treated properly, but it
never will be quite as safe as an internal device.

George