Life, death, and broken software

In a post titled Life, Death, and Splitting Secrets, Jeff Moser presents a software solution for splitting up a password N ways so your loved ones can put the secrets together and get access to critical information from you after your death, using a computer program.

While this shared secret approach is interesting for certain uses, it is unwise for Moser’s stated use… Read the rest of this entry »

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Indexing only null column values in Oracle

We have a table that can have tens or hundreds of millions of rows in it, and in this table there is a certain column. This column usually—typically—generally—has non-null hash values in it.

In unusual cases though, that column can be NULL. And the thing is, there are times when the interesting rows, the rows we want to gather together and do something with, are exactly the rows where that column is null.

Table scans to find the rows where the column is NULL are expensive, so naturally we want to index this column. But since non-null values in this column are a hash and we only ever care about the NULL values, we’d like to avoid the time and space overhead of indexing the non-null values. We’d like a partial index of only the rows where the column is NULL… Read the rest of this entry »

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Change default runlevel (target) on Fedora

I’m running on Fedora 20, and the graphical boot (Plymouth-something-something) sometimes waits a long time and then times out, which when it happens makes the computer take several minutes to boot. This doesn’t happen if I boot to “runlevel 3″ (now called multi-user.target) and then run startx from there.

You can change the default target to “runlevel 3″ like this:
systemctl set-default multi-user.target

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Easy peasy JPGs to PDF conversion

Our scanner at home is an old flatbed that scans to a .jpg file. When you have several pages that you need to scan and send to someone, a pile of JPGs isn’t very nice—you’d rather have one PDF.

If you’re running Linux (at home I’m currently running Fedora 20 – “Heisenbug”), this is easy peasy: with ImageMagick installed, just use the convert command:

convert 1.jpg 2.jpg 3.jpg 1-2-3.pdf

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Mumps-style “dotted do” notation example

FT                                      # A label (for jumping to)
  NEW X,MSG2
  I $$RDVALS^MISC22()=SUCCESS DO QUIT   # The second space between DO and QUIT is significant
  . S X="DO ACTN5^ACTNS"
  . X X                                 # The two Xs mean different things (Cache' is not a context-free language)
  . S MSG2=MSG_" succeeded."            # Expect MSG to float in from somewhere else
  E DO
  . S ERRMSG=INVALIDREADMSG
  . W 1/0

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Method signature joke

STDMETHODIMP CI3DBTranDataSet::GetReal(), man.

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How to have the bash prompt display the full current working directory

To display the full working directory at the bash prompt (Linux command line), edit /etc/bashrc and where the PS1 variable is set, change \W to \w .

I’m running Fedora 19.

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