BTW, here the current version: http://ofps.oreilly.com/titles/9781449396107/architecture.html#archstorage
Please add feedback online too :) On Jul 6, 2011, at 10:37 PM, Lars George wrote: > Hi Florin, > > Note that this was way old stuff. I updated that chapter the last 3-4 days. > Inline... > > 1. How many MemStores can have Region? > HBDG: "A HRegion also has a MemStore" > HBA: "A Store hosts a MemStore". A Store corresponds to a column family for > a table for a given region. > > Each Store has a MemStore. > > 2. How many HLog instances are created per Region Servers? > HBDG:"A HRegion also has [...] a HLog instance" > HBA: "[...]and there is one HLog instance per RegionServer. " > > The HRegion has a reference of the shared HLog, I had already updated that in > the newer version. > > 3. After reading the HBA, I've concluded (please correct me if I'm wrong), > that the are these reletionships > a) A RegionServer has one HLog instance > > Yes, and it is shared with the HRegion instances. > > b) A RegionServer has one .META. table that holds meta information about > many HTable > > Well, one region server "hosts" the .META. region. Basically, the .META. is > just another table, but treated specially. It only has one region (for now) > and that is on one server. Which one is random. > > c) A HTable can be split in many Regions. > > Yes. > > d) A HTable can have many column family > > Yes. > > e) A Column family has one Store > > Yes. > > f) A Store can have zero ore more HFile instances > > Yes, wrapped into StoreFile instances. > > g) A Store can one MemStore > > It has one, yes. > > h) A column family can have zero or many columns > > Well, the CF is just a schema. The actual columns define a row. So if you > define a CF, it will create a directory for it on disk. But if you do not > store any data, then no data resides on disk. > > I'll look forward for your opinions and answers...and please complete with > your knowledge. > > Hope that helps. Sorry for putting the old info into that section, I had > added a disclaimer a few days ago that I am still overhauling this chapter. > It was written for 0.20.x! But as I said, I just finished the overhaul, and > added much more to it. > > Cheers, > Lars > > > Thank you. > Regards, > Florin > >
