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Duplicate Immediate Memberships Issue

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  • From: Shilen Patel <>
  • To: Grouper Dev <>
  • Subject: Duplicate Immediate Memberships Issue
  • Date: Fri, 15 May 2009 16:47:04 -0400

Hi all,

For 1.5, we're working on addressing some of the performance issues with effective memberships. Part of that will mean moving the effective memberships out of the grouper_memberships table. Doing this potentially brings us a step closer to solving another problem.

The issue is that if two processes write immediate memberships for the same member, group/stem, and field before either can do a commit, then we'll end up with two identical membership records in the database.

See --

So one way to solve this would be to use locking on groups and stems during immediate membership adds.

But I think it would be better if we could have a unique constraint on the grouper_memberships table that would just prevent this from happening. However, some databases don't honor unique constraints if part of the key contains a NULL value. The table has columns owner_group_id and owner_stem_id since a membership can either be for a group or a stem and exactly one of the two will always be NULL.

So one way to handle this issue (proposed by Chris) would be to add two more columns (owner_group_id_nulls and owner_stem_id_nulls). These new columns would be identical to owner_group_id and owner_stem_id except if there's a NULL, we would put some string ("<NULL>") in the column instead. There would be no foreign keys on these columns (owner_group_id and owner_stem_id have foreign keys), but the unique constraint would work using the new columns.

Does anyone have any thoughts or suggestions?


-- Shilen

  • Duplicate Immediate Memberships Issue, Shilen Patel, 05/15/2009

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