From: Rui DeSousa <rui@crazybean.net>
To: pavan95 <pavan.postgresdba@gmail.com>
Cc: pgsql-admin@postgresql.org
Subject: Re: Relation between parameters in postgresql.conf file!!
Date: Fri, 2 Nov 2018 10:56:03 -0400
Message-ID: <CB2CFFB1-0FAD-4967-8FD8-C372A3C4351C@crazybean.net> (raw)
In-Reply-To: <1541140765942-0.post@n3.nabble.com>
References: <1541140765942-0.post@n3.nabble.com>
> On Nov 2, 2018, at 2:39 AM, pavan95 <pavan.postgresdba@gmail.com> wrote:
>
>
> 1. vacuum_cost_page_hit
> 2. vacuum_cost_page_miss
> 3. vacuum_cost_page_dirty
>
>
These are tunable parameters to control auto vacuum. Look at vacuum_cost_limit and then consider how the above parameters would affect it.
> 1. autovacuum_vacuum_scale_factor=0.2(20%)
> 2. autovacuum_analyze_scale_factor=0.1(10%)
>
Those are just the factors used to determine when auto vacuum or analyze should vacuum/analyze a table.
> From the below description:
>
>> vacuum_cost_page_hit (integer)
>> The estimated cost for vacuuming a buffer found in the shared buffer cache.
> It represents the cost to lock the buffer pool, lookup the shared hash table
> and scan the content of the page. The default value is one
> 1. Does the vacuum operate on the buffer pool(memory)? Assuming it is
> operated on the data files!!!
> 2. What does the sentence "lock the buffer pool, lookup the shared hash
> table and scan the content of the page" refers to??
>
To do anything with the block in the datafile it first needs to be loaded into the buffer pool thus all associated overhead of that operation.
>> vacuum_cost_page_dirty (integer)
>> The estimated cost charged when vacuum modifies a block that was previously
> clean. It represents the extra I/O required to flush the dirty block out to
> disk again. The default value is 20.
> What does actually happen here?? Why does this generate extra I/O??
>
> What is the meaning of the sentence "It represents the extra I/O required to
> flush the dirty block out to disk again"?? Why does vacuum flush the dirty
> block to disk when writer process does that?
>
Again it’s the same as the other tunable parameters.. it just states the cost of modifying a clean block.
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To: pgsql-admin@postgresql.org
Cc: rui@crazybean.net, pavan.postgresdba@gmail.com
Subject: Re: Relation between parameters in postgresql.conf file!!
In-Reply-To: <CB2CFFB1-0FAD-4967-8FD8-C372A3C4351C@crazybean.net>
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