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Storing data samples with low overheads
by Mark Rogers 04 Jul '12

04 Jul '12

I'm writing an application to run on small ARM units. It collects data from various sources at varying frequencies (up to once per second) and needs to store them. The number of discrete values will vary but we're running tests on around 200 data points dropping the data into MySQL. By "varying frequencies" what I mean is that some items will be read every second, others less frequently (say once every 30mins), so I need a data structure that will cope with that but my tests are currently on the worst-case of storing everything every second (or trying to!) One option is to have a table per item, comprising little more than timestamp and value. Our tests so far have taken 2-5s to store 200 samples this way. We're looking at other ways (eg one table for all samples, storing an item id, timestamp and value). However I can't help think that MySQL is overkill and an overhead we could do without. So, does anyone have any suggestions? We could build our own data storage system - the applications I've seen before that do this would probably have a single binary file per day/week/month of data for any single item, storing a single timestamp (marking the start of the file) and sample period, followed by 4 bytes per sample at the appropriate offset into the file from there; reading or writing just becomes a case of working out which file to look at and the offset into that file. But I'd rather not go quite so low-level if I can avoid it. -- Mark Rogers // More Solutions Ltd (Peterborough Office) // 0844 251 1450 Registered in England (0456 0902) 21 Drakes Mews, Milton Keynes, MK8 0ER

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[ALUG Announce] ALUG Norwich Pub Meet Thursday 12th July
by Viperfang 04 Jul '12

04 Jul '12

ALUG Announce Please send announcements to Announce(a)lists.alug.org.uk Unsub, change settings via http://lists.alug.org.uk/mailman/listinfo/announce ----- Hello Norwich Aluggers, Our monthly ALUG Norwich social meeting will be held this Thursday, 12th July at The Coach and Horses (82 Thorpe Road, Norwich, NR1 1BA). The meeting officially starts at 8pm, although some people may arrive earlier. More information on those people can be found on the list and the IRC channel. If you are unsure if you will recognise us then make yourself and your intent to attend known by either posting on list or visiting us on IRC so we can look out for you rather than hiding in the corner. Optionally you could ask at the bar if they know where the geeky computer weirdos are and they'll point you in the right direction (seriously!). Another possibility is look for heaps of electronics on a table that may possibly look like movie props that would used for detonating explosives. Feel free to bring electronics/laptops/gadgets to the meet, you will by no means be alone. Ben Bewick aka Viperfang NB: This mail is automated, please refer to the usual sources for more information. ALUG Contact Details: Website : http://www.alug.org.uk/ IRC : #alug on irc.alug.org.uk List : http://lists.alug.org.uk/mailman/listinfo Twitter : http://twitter.com/anglianlug Identica: TBA Facebook: http://www.facebook.com/group.php?gid=2381613902 ----- Send discussion replies to main(a)lists.alug.org.uk (Reply-To set) Unsub, change settings via http://lists.alug.org.uk/mailman/listinfo/announce

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2600 meeting at 18:00 on Friday the 6th July.
by Viperfang 03 Jul '12

03 Jul '12

Quick heads up about this months Norwich 2600 meeting, more info at http://www.norwich2600.co.uk

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Lenovo T520
by Paul Grenyer 02 Jul '12

02 Jul '12

Hi All I'm still having lots of wifi and 3G card related problems with my Lenovo T520 and Linux Mint 13 (I though it was 12, it was 13). Does anyone have a similar machine (or even the same machine) that they're successfully working with? Maybe I could pick your brains at one of the pub meets? -- Thanks Paul Paul Grenyer e: paul.grenyer(a)gmail.com b: paulgrenyer.blogspot.com t: pjgrenyer ACCU Member: License to code. (http://www.accu.org)

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2600 meeting at 18:00 on Friday the 1st June.
by Viperfang 29 Jun '12

29 Jun '12

Quick heads up about this months Norwich 2600 meeting, more info at http://www.norwich2600.co.uk

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Open source alternative to full fat Adobe?
by Bev Nicolson 26 Jun '12

26 Jun '12

Evince is great for what it does, imo, but you can't extract pages with it. Does anyone round here know of a good alternative to the full-fat, all singing all dancing but not very cheap Adobe? Does such a thing exist? Bev.

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SOund unavailable on Flash Player
by Ted.Harding＠wlandres.net 24 Jun '12

24 Jun '12

Greetings All! Just now, wanting to play a YouTube video, I found that the sound on Flash Player is turned off, and I can find no way to turn it on again. The "speaker" icon in the bottom bar as an "X" beside it, indicating that it is turned off, and I can find no way to turn it back on again (e.g. clicking on the icon, or on the "X", produces not response; and looking into Settings after right-clicking on the Flash Player screen offers no help). However, everything was fine a few days ago, and I'm not aware of having done anything which might cause this problem. Also, the YouTube video is indeed the same one which I had watched a fews days ago with no problem. Can anyone offer any help with this problem? Adobe Flash Player 10 Iceweasel 3.0.6 (2009) Debian Lenny 2.6.26 ------------------------------------------------- E-Mail: (Ted Harding) <Ted.Harding(a)wlandres.net> Date: 24-Jun-2012 Time: 12:23:35 This message was sent by XFMail -------------------------------------------------

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Wierd hang(s) when using grep
by Chris Green 20 Jun '12

20 Jun '12

Over the past few months I've noticed that when I run grep it sometimes appears to hang, I had put it down to doing "grep -r" down a rather large file hierarchy but now it's happening with a perfectly simple grep:- www-data$ ls *.txt sidebar.txt start.txt www-data$ grep xxx *.txt www-data$ grep fred *.txt www-data$ grep 'CLEARFLOAT' *.txt ... and there it sits, still (like 5 minutes later). The two .txt files are only a few tens of bytes long. It's not using any processor time, it's just stuck. I have just done it again in another terminal window, quotes removed but otherwise the same:- www-data$ grep fred *.txt www-data$ grep CLEARFLOAT *.txt ^C www-data$ ... and with a different user (in the same directory):- chris$ cd /home/www-data/www/wiki/data/pages chris$ grep fred *.txt chris$ grep CLEARFLOAT *.txt ^C chris$ So, what am I missing? -- Chris Green

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Getting MAC address in a shell script
by Mark Rogers 20 Jun '12

20 Jun '12

This works: mac=$(ifconfig eth0 | grep -Eo '..:..:..:..:..:..' | sed -e 's/://g') .. but I'm sure there's a better way. Suggestions? Also, if I have something like: echotemplate="This is my MAC: (MAC)" mac=$(ifconfig eth0 | grep -Eo '..:..:..:..:..:..' | sed -e 's/://g') echo $(echo $echotemplate | sed -e "s/(MAC)/$mac/") .. is there a better way to do the substitution in the last line? I can't swap the top two lines around (one is a user-defined setting at the top of the script, the value of $mac is calculated in the body of the script), otherwise I would just use echo "This is my MAC: $mac" .. which would be nice and easy! But I'm using this as a learning exercise. -- Mark Rogers // More Solutions Ltd (Peterborough Office) // 0844 251 1450 Registered in England (0456 0902) 21 Drakes Mews, Milton Keynes, MK8 0ER

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Getting round lack of suid on scripts (not to become root!)
by Chris Green 20 Jun '12

20 Jun '12

Is there any way to run a script such that it executes as another user than the person running it? Normally (well, old-fashionedly) one would have set the SUID bit in the permissions, made the script owned by the desired user and that would be it but nowadays it no longer works because SUID on scripts is disabled. Is there any reasonably simple way to work round this? All I have found searching so far is to write a short C program to do the SUID change and use that to execute the script. I could do this I suppose but I'd really prefer an easier way to do it as the C program method needs to know both the desired UID and the name of the program to run so, while hardly complex, it will need command line parameters etc. -- Chris Green

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