Обсуждение: Small OS ports & Handheld devices
Seemingly completely opposite to my usual focus on large scale enterprise issues and requirements, I'm looking into PostgreSQL on small handheld devices. Clearly these have limited memory and little "disk" capability... Are there some ports available to various devices? What is the lowest memory footprint PostgreSQL has achieved? [8Mb was last quote] How little disk space has anyone achieved? Is that an available port, or just a set of configure options? Is there a definitive list of supported ports? (for anything) Does PostgreSQL run on? - Windows 2003 (is that part of Win32 port as a defined target?) - PalmOS - Zaurus Related info is copied below: Q: Does PostgreSQL write repeatedly even when there is a no overt SQL write activity? With a write-capable, but very low write rate, PostgreSQL seems a good candidate, given current memory capacities? Dredging up last year's discussion on "postgres on a PDA" we have.. "Al Bean" <albean84 ( at ) hotmail ( dot ) com> writes: > My PDA has 32MB of RAM (well more like 16 with the way Sharp allocates it) > and I use a 256MB FLASH memory card which sort of looks like a hard drive on > the PDA. I know postgresql will run in about 8MB of RAM so I think I should > be ok on this front but I'm wondering about the data residing in > FLASH. Postgres has kind of gotten away from the notion of a small disk footprint :-(. Some things to look at: * Definitely reduce the size of WAL segments (see XLogSegSize). You can't afford the default 16MB. * You probably don't want to have multiple databases. I'd suggest doing all your work in template1. Consider also dropping template0 --- its only value would be to reinit template1, and if you need to do that you might as well re-initdb. But I fear the real problem is going to be that FLASH memory has a limited lifetime (measured in write cycles). Postgres is going to spend that lifetime with abandon, because it has absolutely no motivation to avoid disk writes. Are you prepared to replace the FLASH every so often? ..reply... In article <1883 ( dot ) 1042606899 ( at ) sss ( dot ) pgh ( dot ) pa ( dot ) us>, Tom Lane <tgl ( at ) sss ( dot ) pgh ( dot ) pa ( dot ) us> wrote: >attention I think it was on the order of magnitude of 10000 write >cycles --- which Postgres could blow through in no time. I hope >it's better now, but I dunno by how much. Anyone have more >up-to-date info? Only about 1 order of magnitude better. From the Linux Embedded FAQ: Q: 3.3 Flash Limited write cycles Flash have limited write cycles capabilities from 200 000 to 400 000. Using swap on such device is dangerous. 300 000writes gives you 200 days at 1 write / minute and 83 hours at 1 write / second. More, If you interrupt power at arbitrarytimes while the device is writing, you can lose the integrity of the file system being modified. The loss is notlimited to the 512 byte sector being modified, as it generally is with rotating disks; you can lose an entire eraseblock, maybe 64K at once. The risk goes up as the "disk" approaches full, because erase rewrite cycles happen moreoften in this condition. Un*x file systems spread their super block tables around the "disk", in the hope that at least one will survive a head crash. Create one file, then /bin/sync: what percentage of the device's erase blocks get hit? Thanks, Simon Riggs 2nd Quadrant
Simon Riggs <simon@2ndquadrant.com> writes:
> ... I'm looking into PostgreSQL on small
> handheld devices. Clearly these have limited memory and little "disk"
> capability...
> Are there some ports available to various devices?
I don't know of any supported ports.
> What is the lowest memory footprint PostgreSQL has achieved?
This depends entirely on your postgresql.conf settings and how complex
the queries you want to process are. I would think you could get it
down to maybe 4 or so meg if you have bottom-of-the-barrel requirements.
Performance in this configuration not guaranteed ;-)
> How little disk space has anyone achieved?
> Is that an available port, or just a set of configure options?
IIRC, configuring the WAL segment size is a pg_config_manual.h setting
in CVS tip, but in extant releases you'd have to dig into the xlog code
to adjust it.
> Q: Does PostgreSQL write repeatedly even when there is a no overt SQL
> write activity?
Given a SELECT-only query load, I'd expect PG to reach a state of zero
new writes fairly quickly (at the latest, after a vacuum and checkpoint
have occurred). The real problem is that any single update operation
will generate quite a number of disk writes, the more so the smaller
your shared_buffers setting :-(. It's not at all optimized to minimize
writes in a low-but-not-zero-update-traffic situation. So you'd likely
be facing some issues with FLASH lifetime.
regards, tom lane
Simon Riggs wrote: > Is there a definitive list of supported ports? (for anything) http://www.postgresql.org/docs/7.4/static/supported-platforms.html For example the Linux/arm port can run on many PDA's but because of the write intensity and the limited write cycles of flash memory this continues to be a toy setup.
> Simon Riggs wrote: > > Is there a definitive list of supported ports? (for anything) > > http://www.postgresql.org/docs/7.4/static/supported-platforms.html > > For example the Linux/arm port can run on many PDA's but because of the > write intensity and the limited write cycles of flash memory this > continues to be a toy setup. Why? If you really need PostgreSQL on your PDA don't use Flash. Use an IDE drive. http://www.flash-memory-store.com/ibmmicrodrives.html http://www.memorysuppliers.com/ibmmic1gbwtr.html $369 for 4GB of storage in a compact flash card is not all that bad. $189 for 2.2GB is very reasonable when you consider the 512MB CF is going for $149! These are basically IDE drives in a compact flash form factor, as such they should have lifetimes approaching a regular IDE drive, right? Just don't bounce them around too much. Later Rob
Rob Butler wrote: > $369 for 4GB of storage in a compact flash card is not all that bad. > $189 for 2.2GB is very reasonable when you consider the 512MB CF is > going for $149! The current "cheap" workaround to get a Hitachi (ne IBM) 4GB microdrive is to buy a Creative Muvo2 4GB and open it up to extract the intact (OEM) 4GB drive. $200 in the US typically. Being a digital camera nerd, I pick up these things... now back to the usual traffic. Peter
> Are there some ports available to various devices? > > What is the lowest memory footprint PostgreSQL has achieved? > [8Mb was last quote] > > How little disk space has anyone achieved? > Is that an available port, or just a set of configure options? > > Is there a definitive list of supported ports? (for anything) > > Does PostgreSQL run on? > - Windows 2003 (is that part of Win32 port as a defined target?) It definitly is there fro Windows Server 2003, in the new port. But since you are talking handhelds, are you possibly referring to Windows Mobile 2003? That is a whole different beast, and *not* included in the win32 part (no Win CE variants are) //Magnus
> -----Original Message----- > From: Magnus Hagander [mailto:mha@sollentuna.net] > Sent: 30 April 2004 11:40 > To: Simon Riggs; pgsql-hackers@postgresql.org > Subject: Re: [HACKERS] Small OS ports & Handheld devices > > It definitly is there fro Windows Server 2003, in the new > port. But since you are talking handhelds, are you possibly > referring to Windows Mobile 2003? That is a whole different > beast, and *not* included in the > win32 part (no Win CE variants are) Nor are they likely to be at a guess. I tried compiling libpq using eVC++ 4.0 with the PPC 2003 SDK the other day and got nowhere fast. Regards, Dave
> > It definitly is there fro Windows Server 2003, in the new port. But > > since you are talking handhelds, are you possibly referring > to Windows > > Mobile 2003? That is a whole different beast, and *not* included in > > the > > win32 part (no Win CE variants are) > > Nor are they likely to be at a guess. I tried compiling libpq using > eVC++ 4.0 with the PPC 2003 SDK the other day and got nowhere fast. Not having looked at the code, I think you are going to have a much easier time looking at npgsql and the Compact Framework, if you developer on the PPC and want just the client. I even think I saw some messages about there being support included in npgsql already, but I'm not sure. Even if not, it shouldn't be *all* that hard to get it running - probably significantly easier than libpq. //Magnus
> -----Original Message----- > From: Magnus Hagander [mailto:mha@sollentuna.net] > Sent: 30 April 2004 13:01 > To: Dave Page; Simon Riggs; pgsql-hackers@postgresql.org > Subject: RE: [HACKERS] Small OS ports & Handheld devices > > Not having looked at the code, I think you are going to have > a much easier time looking at npgsql and the Compact > Framework, if you developer on the PPC and want just the > client. I even think I saw some messages about there being > support included in npgsql already, but I'm not sure. Even if > not, it shouldn't be *all* that hard to get it running > - probably significantly easier than libpq. Yeah, I did consider that (I was one of the Npgsql hackers in the early days). Looks like it will actually make more sense *in this case* to use WinInet and write a middle tier in PHP though. Which is what I'm currently doing :-) Regards, Dave