Re: bloat indexes - opinion

2017-02-25 17:53 GMT+13:00 Patrick B <patrickbakerbr(at)gmail(dot)com>:

>
>
> 2017-02-23 11:46 GMT+13:00 Jeff Janes <jeff(dot)janes(at)gmail(dot)com>:
>
>> On Tue, Feb 21, 2017 at 1:44 PM, Patrick B <patrickbakerbr(at)gmail(dot)com>
>> wrote:
>>
>>> Hi guys,
>>>
>>> I've got a lot of bloat indexes on my 4TB database.
>>>
>>> Let's take this example:
>>>
>>> Table: seg
>>> Index: ix_filter_by_tree
>>> Times_used: 1018082183
>>> Table_size: 18 GB -- wrong. The table is mostly on pg_toast table. Its
>>> real size is 2TB
>>> Index_size: 17 GB
>>> Num_writes 16245023
>>> Index definition: CREATE INDEX ix_filter_by_tree ON seg USING btree
>>> (full_path varchar_pattern_ops) WHERE (full_path IS NOT NULL)
>>>
>>>
>> What is this from? If you think the table size reported should include
>> toast, then change it to do that, or request the author of whatever-this-is
>> to make that change.
>>
>> What indication is there that the index is bloated? If the
>> meat-and-potatoes of a table is held in toast, then wouldn't you expect the
>> size of the table and the size of the index to be about the same?
>>
>> Cheers,
>>
>> Jeff
>>
>
>
> I am running queries to see bloat indexes [1]. Also i understand an index
> can't have same size as table.
> If you have any other table that can prove the index is indeed bloat,
> please let me know and i will be happy to post results here.
>
> [1] https://wiki.postgresql.org/wiki/Index_Maintenance
>
> Patrick
>
>

FYI - using this query to see the index size:

SELECT idstat.schemaname AS schema,

idstat.relname AS table_name,

indexrelname AS index_name,

idstat.idx_scan AS times_used,

pg_size_pretty(pg_relation_size(quote_ident(idstat.schemaname) ||
'.' || quote_ident(idstat.relname))) AS table_size,

pg_size_pretty(pg_relation_size(quote_ident(idstat.schemaname) ||
'.' || quote_ident(indexrelname))) AS index_size,

n_tup_upd + n_tup_ins + n_tup_del as num_writes,

indexdef AS definition

FROM pg_stat_user_indexes AS idstat

JOIN pg_indexes ON indexrelname = indexname

JOIN pg_stat_user_tables AS tabstat ON idstat.relname = tabstat.relname

WHERE indexrelname = 'index_name';