What’s different?

Differences to the old MultiDark Database (www.multidark.org)

Please report any problems to us (Contact form), so we can fix them.
If you encounter heavy problems here, you can still fall back to the older webpage at www.multidark.org, though new data sets (after MDPL) won’t be available there. If any major problems occur with the MultiDark-server, it is likely going to be switched off.

So, what’s actually new? You’ll have realized that we use a completely new web application now (see Links and References for the software behind it). You can still enter SQL queries into an SQL form, but jobs will be send to a job queue. If you want to script your queries, have a look into chapter Data access. The results are now stored in private user tables and can be retrieved at any time. There’s no expire date for these tables so far, but we may apply one in the future.

At the backend, we needed more power to answer your queries faster, and so we switched to the parallel MySQL spider engine and developed PaQu for reformulating the queries. An extensive documentation for PaQu can be found in section PaQu. In comparison to using the Microsoft SQL Server (used for the older MultiDark Database), some things need to be changed or used with care. Here’s a list of what you need to keep in mind:

MySQL-related changes

  • Case-sensitive database and table names
    The databases and tables are stored in directories and files on a Unix system and thus
    their names are case-sensitive.

    SELECT * FROM mdr1.redshifts

    won’t work. You must use the correct case as given by the database browser below the query form:

    SELECT * FROM MDR1.Redshifts

    Also use back-tics ` for special column names (e.g. if refering one of the columns in a result-table).

  • . instead of ..
    use “.” to separate between database and table name, e.g.

    SELECT * FROM MDR1..redshifts

    will now be

    SELECT * FROM MDR1.redshifts
  • LIMIT instead of TOP
    use LIMIT instead of TOP to limit your results to a given number of rows
    A query like

    SELECT TOP 10 fofId, x,y,z FROM MDR1..FOF

    must be replaced by

    SELECT fofId, x,y,z FROM MDR1.FOF LIMIT 10

    Please note that using LIMIT for pagination (i.e. phrases like LIMIT 20,10) won’t work as expected, since this will be applied to each node individually and no assumptions can be made about the distribution of data on the individual server nodes. In short: Don’t use pagination! Use proper selection via physical properties instead.

  • No common table expressions – use subqueries
    MySQL does not support the (non standard) common table expressions of MS SQL (WITH ... AS ...). Instead, you need to rewrite your query into a nested query.

PaQu/Spider related issues

I moved these to another page, to get more visibility. Please find them now here:
PaQu issues.

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