Monthly Archives: November 2009

Linux OOM Killer

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The Linux OOM Killer heuristic can be summed up as:

  1. Run out of memory.
  2. Kill PostgreSQL.
  3. Look for processes that might be using too much memory, and kill them, hopefully freeing memory.

Notice that step #2 is independent of factors like:

  • Is PostgreSQL consuming a significant share of the memory resources?
  • Will killing PostgreSQL alleviate any memory pressure at all? Continue reading →

Temporal Keys, Part 2

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In the last article, I argued that:

  • A schedule conflict is a typical business problem.
  • The later you try to resolve a schedule conflict, the more costly it is to resolve.
  • In particular, there is a big jump in the cost the moment after conflicting data is recorded.
  • Therefore, it’s best for the DBMS itself to enforce the constraint, because only the DBMS can avoid the conflict effectively before the conflict is recorded.

Then, I opened up a discussion to see how people are dealing with these schedule conflicts. In the comments I received at the end of the article, as well as other anecdotes from conferences, user groups, mailing lists, and my own experience, the solutions fall into a few categories:

Continue reading →

Temporal Keys, Part 1

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“Schedule conflict” — it’s one of the simplest and most common constraints for business or any other organization. One person cannot be in two places at the same time; and in many cases a only a single person can use a given resource at any time.

Does your database system know anything about a schedule conflict? Should it?

Constraints are always enforced at some point, it’s just a matter of when, how, and the cost of correcting the situation.

Continue reading →