RFR (S) 8227123: Assertion failure when setting SymbolTableSize larger than 2^17 (131,072)

[coleen.phillimore at oracle.com]

On 7/23/19 11:45 AM, Jiangli Zhou wrote:
> On Tue, Jul 23, 2019 at 8:35 AM <coleen.phillimore at oracle.com> wrote:
>>
>>
>> On 7/23/19 11:25 AM, Jiangli Zhou wrote:
>>> Hi Coleen,
>>>
>>> On Mon, Jul 22, 2019 at 12:51 PM <coleen.phillimore at oracle.com> wrote:
>>>> Thanks Jiangli, and for the suggestion to increase the max size.  I was
>>>> waffling about removing the experimental option completely.
>>> Would it be worth considering making SymbolTableSize a product flag?
>>> There was a noticeable performance issue for a large application with
>>> older JDK versions. It was found to be related to slow
>>> SymbolTable::lookup due to too many collisions. Setting a large
>>> initial symbol table size worked around the performance issue and the
>>> improvement was significant. With newer JDK (> 12), user may still
>>> prefer setting a large initial size to avoid any potential overhead
>>> (avoid resizing) for large applications.
>> I think the cost of resizing is low enough that it's not worth making it
>> a product flag.  I know it doesn't match StringTableSize in this way.
>> Ideally, customers should not have knowledge that these things are
>> hashtables and should not have controls for internal implementation
>> decisions.
>>
>> With resizing, both of these tables should perform acceptably out of the
>> box.   Do we have any recent cases of customers needing to set this
>> value to a large size, that may have prompted your bug report?
> That was indeed the case, though it was with older JDK.

Okay, that's good that it wasn't for the latest JDK. 
https://bugs.openjdk.java.net/browse/JDK-8019375 This bug has the 
history of why we made SymbolTableSize experimental, which still holds 
today, so I want to leave it as experimental.  I'm thinking in the 
future we could make StringTableSize experimental to match, and someday 
remove both, but not just now.

Thanks,
Coleen

>
> Best regards,
> Jiangli
>> Coleen
>>
>>> Best regards,
>>> Jiangli
>>>
>>>> Coleen
>>>>
>>>> On 7/22/19 3:40 PM, Jiangli Zhou wrote:
>>>>> Looks good.
>>>>>
>>>>> Best regards,
>>>>> Jiangli
>>>>>
>>>>> On Mon, Jul 22, 2019 at 11:46 AM <coleen.phillimore at oracle.com> wrote:
>>>>>> Summary: Increase max size for SymbolTable and fix experimental option
>>>>>> range.  Make experimental options trueInDebug so they're tested by the
>>>>>> command line option testing
>>>>>>
>>>>>> open webrev at http://cr.openjdk.java.net/~coleenp/2019/8227123.01/webrev
>>>>>> bug link https://bugs.openjdk.java.net/browse/JDK-8227123
>>>>>>
>>>>>> Tested locally with default and -XX:+UseZGC since ZGC has a lot of
>>>>>> experimental options.  I didn't test with shenanodoah.
>>>>>>
>>>>>> I will test with hs-tier1-3 before checking in.
>>>>>>
>>>>>> Thanks,
>>>>>> Coleen