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From John Wilson <sami.hailu...@gmail.com>
Subject Re: Page Locking vs Entry-level Locking
Date Tue, 13 Feb 2018 13:51:30 GMT
Hi Pavlov,

Thanks for your explanation. However, I still have these questions:

   1. If locking is per page-level and there are no entry-level locks, then
   why does the documentation here talk about having entry-level transaction
   locks? https://apacheignite.readme.io/docs/transactions
   2. I'm not clear with what "locking a durable memory region segment "
   means, what is a segment? Does a page contain multiple segments or a
   segment contains multiple pages? The mental picture I have is: a memory
   region is divided into pages (which can be meta data pages, index, or data
   pages). Index pages hold links to data page id and offset for key-value
   pairs while data pages contain the actual key-value pairs. So, what really
   is a segment and what does locking a memory segment means? I understanding
   page-locks, what is segment lock?

Appreciate your response!!!

On Tue, Feb 13, 2018 at 2:32 AM, Dmitry Pavlov <dpavlov.spb@gmail.com>

> Hi John,
> 1. No, content modification require lock holding to page to provide
> consitency in multithreaded environment.
> 2. Page is locked for read before reading its content, and unlocked after.
> Same for lock for write for writting. 1 writer or N readers allowed for
> page. On unlock write lock, dirty flag for page may be set if there data
> was actually modified.
> 3. Lock has per-page basis, additional striping by any offest within page
> is not required accoring to tests.
> Only one contention is observed sometimes in high load test, it is
> contention of threads to lock to durable memory region segment. But this
> situation can be handled by setting concurrenclyLevel in
> DataStorageConfiguration.
> Sincerely,
> Dmitriy Pavlov
> вт, 13 февр. 2018 г. в 9:56, John Wilson <sami.hailu.15@gmail.com>:
> > Hi,
> >
> > Ignite documentation talks about entry-level locks and the page structure
> > has a LOCK_OFFSET that I assume is used to store tag info. I have these
> > questions.
> >
> >    1. Does Ignite use a lock-free implementation to lock pages and/or
> >    entries?
> >    2. When is a page locked and when is it released?
> >    3. When an entry is inserted/modified in a page, is the page locked
> >    (forbidding other threads from inserting entries in the page)? or only
> > the
> >    entry's offset is locked? (allowing other threads to insert/modify
> other
> >    items)
> >
> > Thanks!
> >

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