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From: Evgeniy Shishkin <[email protected]>
To: Tom Lane <[email protected]>
Cc: Andreas Joseph Krogh <[email protected]>
Cc: pgsql-performance <[email protected]>
Subject: Re: Searching GIN-index (FTS) and sort by timestamp-column
Date: Wed, 16 Mar 2016 18:04:08 +0300
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>
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> On 16 Mar 2016, at 17:52, Evgeniy Shishkin <[email protected]> wrote:
> 
> 
>> On 16 Mar 2016, at 16:37, Tom Lane <[email protected]> wrote:
>> 
>> Andreas Joseph Krogh <[email protected]> writes:
>>> 1. Why isnt' folder_id part of the index-cond?
>> 
>> Because a GIN index is useless for sorting.
> 
> I don't see how gin inability to return sorted data relates to index condition.
> In fact i tried to reproduce the example,
> and if i change folder_id to int from bigint, then index condition with folder_id is used
> 
>         Index Cond: ((fts_all @@ '''hi'''::tsquery) AND (folder_id = 1))
> 

Looks like documentation http://www.postgresql.org/docs/9.5/static/btree-gin.html
is lying about supporting int8 type

> 
>> 
>>> 2. Is there a way to make it use the (same) index to sort by 
>>> received_timestamp?
>> 
>> No.
>> 
>>> 3. Using a GIN-index, is there a way to use the index at all for sorting?
>> 
>> No.
>> 
>>> 4. It doesn't seem like ts_rank uses the index for sorting either.
>> 
>> Same reason.
>> 
>> 			regards, tom lane
>> 
>> 
>> -- 
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