The word executor helped me nail down my thoughts (thanks Earwin). I think we should decouple MS into MergeExecutor and MergeScheduler.
ME would control how merges are done: serial, parallel, queue-based (control the level of parallelism) etc. MS would schedule the merges (perhaps a different name is needed). It can be a blocking one (in the sense that the app thread is blocked) or a non-blocking one. It can limit the merges to run a specified amount of time and then abort, etc. I think that all merges block other merges? Anyway, this can be a type of MS too if it isn't the case already. Point is - the decision I make about how should the merges affect my app threads or how long do they take, is not related to how the merges are executed. This will give a nice breakdown of responsibilities between: 1) MP - decides which segments to merge at all 2) ME - executes the merges 3) MS - cotrols all the merges from a high level, mostly the app-level. If we want to consider some further refactoring to IW, we could even tie all three of them together - MS would know of both ME and MP, and IW would interact w/ MS only. This I admit is something that just popped into my mind when writing this email, so perhaps it doesn't make a lot of sense and needs some more mulling. Maybe MS should be renamed to MergeManager or something? Though I'm fine w/ MS too. Shai On Friday, May 28, 2010, Earwin Burrfoot <[email protected]> wrote: > We just need an Executor-based MS, then we can throw all other out of > the window, as threading concerns are now resolved by a proper choice > of Executor supplied to constructor. > Also an application has much more control over threading in > multiple-index situations, as single Executor can be reused for > multiple MSs. > > On Fri, May 28, 2010 at 18:36, Michael McCandless > <[email protected]> wrote: >> Hmm... so I think the questions really are "how many merges are >> allowed to run concurrently?" (SMS is 1 and CMS is N), and "do I spawn >> my own threads for merging or do I steal the app's threads" (SMS >> steals app threads and CMS spawns new ones). >> >> Of course if you steal app threads you can only make use of as much >> concurrency as the app's threads... >> >> Both SMS and CMS will allow other indexing ops to proceed, to a point, >> but if the other indexing ops spawn too many merges, then those >> threads will be blocked by both SMS and CMS. >> >> So I'm not sure blocking/non-blocking is a good first split -- even >> SMS isn't blocking other app indexing threads. >> >> Mike >> >> On Thu, May 27, 2010 at 3:58 AM, Shai Erera <[email protected]> wrote: >>> Hi >>> >>> I've been thinking recently why are these two named like they are ... with a >>> MS we're basically asking two questions: (1) should it block other merges >>> from happening (or app thread from continuing) and (2) should it do its >>> merges concurrently? >>> >>> SMS answers 'true' to (1) and 'false' to (2), while CMS answers the >>> opposite. >>> >>> BUT, there's really no reason why these two are coupled. E.g. someone who >>> wants to block other merges from running, or hold the app thread until >>> merges are finished, does not necessarily want the merges to run in >>> sequence. Those are two different decisions. Even if you want to block the >>> application thread and other merges, you can still benefit form having the >>> merges run concurrently. >>> >>> So, I was thinking that what we really want is a BlockingMS and >>> NonBlockingMS that can be used according to the answer you look for in (1), >>> and then we can have variants for both that execute the merges concurrently >>> or not. I think that serial merging should be supported w/ BlockingMS only, >>> but am interested in other opinions. One of the scenarios for serial merging >>> is if the application wants to ensure no additional threads are spawned >>> other than what it decided to spawn, and therefore it can only be used w/ >>> the BlockingMS.Another scenario is to control IO, but in this case a >>> NonBlockingSerialMS may fit as well (depends if you think other merges may >>> start while this one is running). >>> >>> In fact, w/o changing much, we can have CMS optionally block other merges / >>> app thread by waiting until all merges are finished. We may even stick w/ >>> the current SMS/CMS names, just documenting that CMS can be used to block >>> threads, only merges will be done concurrently. >>> >>> What do you think? >>> >>> Shai >>> >> >> --------------------------------------------------------------------- >> To unsubscribe, e-mail: [email protected] >> For additional commands, e-mail: [email protected] >> >> > > > > -- > Kirill Zakharenko/Кирилл Захаренко ([email protected]) > Phone: +7 (495) 683-567-4 > ICQ: 104465785 > > --------------------------------------------------------------------- > To unsubscribe, e-mail: [email protected] > For additional commands, e-mail: [email protected] > > --------------------------------------------------------------------- To unsubscribe, e-mail: [email protected] For additional commands, e-mail: [email protected]
