Re: [Firebird-devel] AutoOptimize

[Alex P. <pe...@in...>]

Vlad Horsun:
>>>> I.e., if we mark some thread as low IO priority, we may delay IO requests from it 
>>>
>>>     How much delay ? This is a central point
>>>
>> As a first approach we may delay them as long as there are other active 
>> disk requests.
> 
>     This is not good, imo. Such low-priority thread will always sleep if we have even 
> small but regular IO load, i guess. 
>  

Certainly. But as far as I understand, it must sleep in such cases. Or 
there is no reason to make it low IO priority. Certainly, we can invite 
a lot - let single request pass after N high-priority requests provided 
total requests number is less or equal to M. Having M and N settable 
from firebird.conf:). Do we need such overcomplicated things?

>> But adding IO priority control to, for example, 2.0.1 is not a thing I 
>> want to agree with. Too serious change for point release, is not it? As 
> 
>     Nobody offer to add it into 2.0.1. At least not me ;)
> 
>> an opposite we may run statistics auto-update with normal priority. It 
> 
>     I see no good reason to implement auto-update index statistics even in 2.1
> Until we have histogramms we don't need this feature. IMO, of course
>>From the another POV - it is good to have for PR :)
> 

Well, it seemed to me that we talk about things to be done soon.

>> seems it will not break whole system throughput as much as bad plans do 
> 
>     It depends. Yes, our indices are very dense and we need smaller IO to read 
> leaf level compared to other DBMS, but it is very CPU intensive. 
> 

BTW, when we add (or delete) record to index block, it seems we can 
easily detect, do we add unique or duplicated record? Is not this 
information enough to adjust selectivity dynamically?

>> now. Anyway for future versions (remember prepared statements cache ?) 
>> it will require more common solution.
> 
>     My current worries is cache_writer and garbage_collector threads
> 

You've called thread "AutoOptimize" :)

But what's a problem with this threads? Do you want to make them low IO 
priority? Not good idea, I'm afraid.