Horton

Re: unlogged tables vs. GIST

Heikki Linnakangas <hlinnakangas@vmware.com>

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From: Heikki Linnakangas <hlinnakangas@vmware.com>
To: Jeevan Chalke <jeevan.chalke@enterprisedb.com>
Cc: Robert Haas <robertmhaas@gmail.com>, Tom Lane <tgl@sss.pgh.pa.us>, pgsql-hackers@postgresql.org
Date: 2013-01-15T18:10:05Z
Lists: pgsql-hackers

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  1. The GiST scan algorithm uses LSNs to detect concurrent pages splits, but

On 15.01.2013 08:54, Jeevan Chalke wrote:
> For (2), I have added a new function called, GetXLogRecPtrForUnloogedRel()
> which returns a fake LSN for GiST indexes. However, I have removed
> GetXLogRecPtrForTemp() function and added its functionality inside this new
> function itself to avoid complexity.

I don't much care for using a new field in the control file for this. 
First, it seems like a big modularity violation to store a gist-specific 
counter in the control file. Second, you'd be generating a lot of 
traffic on the ControlFileLock. It's not heavily contended at the 
moment, but when the control file is updated, it's held over an fsync, 
which could cause unnecessary stalls to insertions to unlogged gist 
tables. And it's just a bad idea to share a lock for two things with 
completely different characteristics in general.

Could we stash the counter e.g. in the root page of the index?

- Heikki