| From: | Gokulakannan Somasundaram <gokul007(at)gmail(dot)com> |
|---|---|
| To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
| Cc: | "simon(at)2ndquadrant(dot)com" <simon(at)2ndquadrant(dot)com>, PG Hackers <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: Lazy Snapshots |
| Date: | 2009-08-22 18:51:21 |
| Message-ID: | 9362e74e0908221151q25254acla85ce0f858161ad0@mail.gmail.com |
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| Lists: | pgsql-hackers |
> The maintenance costs and update contention for such a datastructure
> would render this completely impractical, even if consulting it were
> free.
>
Thanks for the reply.
a) Only one transaction would be updating its commit status. Its multiple
readers Vs Single Writer for the position of a particular transation( a
memory location ). So a reader-writer lock would reduce the contention.
Moreover it releases the need for the synchronization that happens with
global pg_procs now. For example something like a select which would only
query the old data will never access this structure.
I am right now not able to think of anything on the maintenance cost
perspective.
Gokul.
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