Re: [RFC] LSN Map

From: Bruce Momjian <bruce(at)momjian(dot)us>
To: Marco Nenciarini <marco(dot)nenciarini(at)2ndquadrant(dot)it>
Cc: PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: [RFC] LSN Map
Date: 2015-01-07 15:16:19
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On Wed, Jan 7, 2015 at 10:50:38AM +0100, Marco Nenciarini wrote:
> Implementation
> --------------
> We create an additional fork which contains a raw stream of LSNs. To
> limit the space used, every entry represent the maximum LSN of a group
> of blocks of a fixed size. I chose arbitrarily the size of 2048
> which is equivalent to 16MB of heap data, which means that we need 64k
> entry to track one terabyte of heap.

I like the idea of summarizing the LSN to keep its size reaonable. Have
you done any measurements to determine how much backup can be skipped
using this method for a typical workload, i.e. how many 16MB page ranges
are not modified in a typical span between incremental backups?

Bruce Momjian <bruce(at)momjian(dot)us>

+ Everyone has their own god. +

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