What you say is accurate. I have fixed this issue in our engine, but I just wanted to make you aware of it.
On Mon, Mar 11, 2013 at 4:56 PM, Sergei Petrunia <pser...@askmonty.org> wrote: > Hi Zardosht, > > On Thu, Mar 07, 2013 at 11:08:01PM -0500, Zardosht Kasheff wrote: >> I have found an interesting issue with index condition pushdown. I do >> not know if it is a bug, or if I am misusing the feature. >> >> I have found that in one scenario, when performing a join, an index >> condition is pushed down, but because handler->end_range is not set, >> handler_index_cond_check never returns ICP_OUT_OF_RANGE, even though >> we are out of range. > > Confirm. I have looked how it works in MyISAM and InnoDB. Indeed, they > consider > scan over equality to be a special case. They remember the lookup key and > check it themselves. > > That is, if one does > > h->index_read(key='foo')=0 > h->index_next_same() > > then index_next_same() will check whether the next index tuple has key='foo'. > If the key is different, it will return HA_ERR_END_OF_FILE without checking > the index condition. > > I'm hesitant to say that this is "by design", I'd say that the available > storage engines happened to work this way, and then ICP used that. > > Maybe, this means that implementation of handler::index_next_same() should > set handler::end_range. If it did, a storage engine will be able to support > ICP without implementing index_next_same() call. > > The question for MariaDB is, does it make sense for us to make this change in > MariaDB, when Oracle doesn't support it? > > (As far as I understand, TokuDB will still need to support MySQL, and so will > have to work around the problem by supporting index_next_same() and comparing > the keys like MyISAM/InnoDB do. When you have to do that anyway, there is no > benefit from having this problem fixed in MariaDB...) > >> >> Here is the relevant stack trace, I cannot yet send the entire trace >> as it may include customer information, and I need to double check it >> is ok to send: > <skip> > >> >> In this stack, we are performing an index_next_same, and a condition >> has been pushed down. When we call handler_index_cond_check. we always >> get ICP_NO_MATCH and never get ICP_OUT_OF_RANGE, even though we go >> past the key that we should be retrieving. >> >> Is this by design? Is this a bug? >> > -- > BR > Sergei > -- > Sergei Petrunia, Software Developer > Monty Program AB, http://askmonty.org > Blog: http://s.petrunia.net/blog _______________________________________________ Mailing list: https://launchpad.net/~maria-developers Post to : maria-developers@lists.launchpad.net Unsubscribe : https://launchpad.net/~maria-developers More help : https://help.launchpad.net/ListHelp
