[pgpool-general: 7639] Re: Pgpool query caching
Tatsuo Ishii
ishii at sraoss.co.jp
Mon Jul 12 15:27:49 JST 2021
> Hi,
>
> After enabling memory_cache_enabled = on, got the following in log:
> 2021-07-09 02:53:52: pid 110880: LOG: error while deleting item from shmem
> cache, item: 86 was already deleted
> 2021-07-09 02:53:52: pid 110880: LOG: error while deleting item from shmem
> cache, item: 86 was already deleted
> 2021-07-09 02:53:52: pid 110880: LOG: error while deleting item from shmem
> cache, item: 86 was already deleted
> 2021-07-09 02:53:52: pid 110720: LOG: pool_reuse_block: blockid: 3
>
> May I know what might be the cause?
Do those messages appear frequently? If not, I think they are harmless
and you can safely ignore (downgrading the messages from LOG to DEBUG
is in my plan).
> * num_cache_hits | num_selects | cache_hit_ratio | num_hash_entries |
> used_hash_entries | num_cache_entries | used_cache_entries_size |
> free_cache_entries_size | fragment_cache_entries_size
> ----------------+-------------+-----------------+------------------+-------------------+-------------------+-------------------------+-------------------------+-----------------------------
> 7797
> | 33619 | 0.19 | 1048576 | 858
> | 858 | 872837 | 62534330
> | 3663873(1 row)*
>
> As per this cache status is it recommended to enable cache?
No. We generally recommend to enable cache if the cache hit rate is
higher than 0.7 (70%).
> Is there any option to enable query caching only for selected tables?
Yes, you can use cache_safe_memqcache_table_list or
cache_unsafe_memqcache_table_list.
Best regards,
--
Tatsuo Ishii
SRA OSS, Inc. Japan
English: http://www.sraoss.co.jp/index_en.php
Japanese:http://www.sraoss.co.jp
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