July 2013 - database-devel

Esquleto : 'ORDER BY random()'?
by Erik de Castro Lopo 12 Jul '13

12 Jul '13

Hi all (and specifically Felipe), I'm wonder who to implement the following SQL in Esqueleto: SELECT * FROM table WHERE field = X ORDER BY RANDOM() LIMIT N I noticed that there is a random_ function and I figured out how to use it by reading the tests, but it doesn't seem to be useful in the above context. Clues? Maybe Esqueleto needs an 'orderByRandom'. Cheers, Erik -- ---------------------------------------------------------------------- Erik de Castro Lopo http://www.mega-nerd.com/

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Request for Feedback on COPY IN/OUT support for postgresql-simple
by Leon Smith 12 Jul '13

12 Jul '13

Although the postgresql-libpq binding has supported both COPY IN and COPY OUT for some time now, this functionality wasn't available to postgresql-simple without mucking around in the Internal module to call libpq functions on your own. I just now fixed that. The interface I went with ultimately mimics the libpq interface rather closely, albeit with many simplifications. I did consider offering fold-like combinators, and while they would certainly be much more convenient for some use cases, they also introduce a number of complications, such as dealing with exceptions. If anybody's interested in reviewing these latest patches, I'd appreciate it. I suppose the one thing I'm most unsure about is exactly which exceptions should be raised under various conditions. https://github.com/lpsmith/postgresql-simple/commit/491247f687fcbfd30c8b0f5… https://github.com/lpsmith/postgresql-simple/commit/4cfcdbee22a0cb1fb798598… Best, Leon

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Announcing postgresql-libpq-0.8.2.3
by Leon Smith 09 Jul '13

09 Jul '13

I just fixed a fairly serious performance problem with postgresql-libpq's binding to PQescapeStringConn; in was exhibiting a non-linear slowdown when more strings are escaped and retained. https://github.com/lpsmith/postgresql-libpq/commit/adf32ff26cdeca0a12fa5965… If you are using postgresql-libpq's escapeStringConn, or a library that uses it (e.g. postgresql-simple, or persistent-postgresql), I do recommend upgrading. You may or may not see a performance improvement, depending on your particular use case, but if you do it can be quite substantial. It's not entirely clear to me what the root cause really is, but it certainly appears as though it's related to the (direct) use of mallocBytes, which was replaced with (indirect) calls to mallocForeignPtrBytes / mallocPlainForeignPtrBytes (through the bytestring package). In this case, it resulted in an asymptotic improvement in time complexity of some algorithms. Best, Leon

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