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Re: database slowness weirdness
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Re: database slowness weirdness


  • Subject: Re: database slowness weirdness
  • From: Jonathan Rochkind <email@hidden>
  • Date: Mon, 26 Apr 2004 16:47:52 -0500

I think that MS SQL Server may sometimes do table level locking even when a better db woudln't have to. But in this case, maybe even a better db would have to.

The more I think about it, the more I think I know the problem though. Yes, lots of other stuff accesses this table. It is the "User" table for my content management system, so of course it gets lots of use. But in particular, I have one part of my app that does a SELECT with sub-query, and it's querying this User table. The sub-select is not to a single table, but in fact involves a join itself. I have noticed that MS SQL Server does not perform well with a sub-query which involves a join. In some cases, that query can take 10 or more seconds to execute (if the sub-query did not involve two tables, but just involved one table, MS SQL Server does a lot better with it).

So I put that in a WOLongResponse, figured okay, it might take a while to execute, no big deal.

But now I'm worried that for as long as it takes to execute, nobody else can get in to do an UPDATE to that table. And since an UPDATE to that table is done every time someone logs in... that's bad. It keeps people from logging in.

Okay, time to go and fix my logic so a sub-select is not needed. Too bad, because this forces me to have some much messier code (there's a lot of abstraction going on, unfortunately).

--Jonathan

At 2:26 PM -0700 4/26/04, Chuck Hill wrote:
Sounds like the db / your connection is doing table level locking instead of row level locking. Or something is reading or updating so much of that table that the entire thing is being locked. Is anything else accessing the table?


On Apr 26, 2004, at 1:35 PM, Jonathan Rochkind wrote:

I guess there's something bad going on with db-level locking. The db is locking out that update SQL because someone else is doing something that requires a db-level lock. All underneath the hood---none of my code explicitly aquires a lock, but maybe a lock is implied by an 'update' whether you like it or not. I don't really know what I'm talking about, I'm just guessing here, in case anyone has anything useful to suggest.
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References: 
 >database slowness weirdness (From: Jonathan Rochkind <email@hidden>)
 >Re: database slowness weirdness (From: Chuck Hill <email@hidden>)

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