Always use the C Locale with PostgreSQL
I ran into the weirdest bug with Bricolage today. We use the
LIKE operator to
do string comparisons throughout Bricolage. In one usage, the code checks to see
if there’s a record in the “keyword” table before creating it. This is because
keyword names are unique. So it looks for a keyword record like this:
SELECT name, screen_name, sort_name, active FROM keyword WHERE LOWER(name) LIKE ?
If it finds a keyword, it creates a relationship between it and a story document. If it doesn’t find it, it creates a new keyword record and then associates the new keyword with a story document.
However, one of our customers was getting SQL errors when attempting to add
keywords to a story, and it took me a while to figure out what the problem was.
This is because I couldn’t replicate the problem until I started trying to
create multibyte keywords. Now, Bricolage uses a UTF-8 PostgreSQL database, but
something very odd was going on. When I attempted to add the keyword “북한의”,
it didn’t find an existing keyword, but then threw an error when the unique
index thought it existed already! Running tests in
psql, I found that
would find the existing record, but
Once I posted a query on the pgsql-general list, someone noticed that the
record returned when using
= actually had a different value than was
actually queried for. I had searched for “북한의”, but the database found
“국방비”. It seems that
= compares bytes, while
LIKE compares characters.
The error I was getting meant that the unique index was also using bytes. And
because of the locale used when
initdb was run, PostgreSQL thought that they
actually were the same!
The solution to this problem, it turns out, was to dump the database, shut down
PostgreSQL, move the old data directory, and create a new one with
initdb -locale=C. I then restored the database, and suddenly
(and the unique index) were doing the same thing. Hallelujah!
Naturally, I’m not the first to notice this issue. It’s particularly an issue
with RedHat Linux installations, since RedHat has lately decided to set a
system-wide locale. In my case, it was “en_US.UTF-8.” This apparently can break
collations in other languages, and this affects indices, of course. So I was led
to wonder if
initdb shouldn’t default to a locale of
C instead of the
system default. What do you think?
You can read the whole thread here.
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