Very impressive! The long running transaction problem has plagued the
system from the days of Groton Database Systems. A solution is long overdue.
On Friday, October 10, 2014, Nikolay Samofatov <
nikolay.samofa...@red-soft.biz> wrote:
> Hello, All!
>
> I have mostly completed my work for statement-level read consistency in
> READ COMMITTED mode and
> implementation of intermediate versions GC as suggested by Jim Starkey.
>
> Please have a look at the patch against current Firebird 3:
> https://drive.google.com/open?id=0B9tc80DCcxtrNWtpSnBDNUdKcGc&authuser=0
>
> The patch includes the following changes:
>
> 1. Read Committed transactions have statement-level read consistency
> semantics by default
> 2. New atomics code, uses libatomic_ops for all platforms
> 3. Shared database counters moved to shared memory
> 4. TIP cache (TPC) moved to shared memory and is implemented using
> lock-free algorithms
> 5. Snapshot (isc_tpc_concurrency) mode transactions now use shared TIP
> cache and not a private copy of TIP bitmap
> 6. Lock manager data is now ULONG (to allow 2^32-1 transactions)
> 7. Intermediate versions GC, performed:
> - when unneeded version is read by VIO_chase_record_version
> - by GC and sweep threads (special logic)
> - during index creation (prevents false duplicates)
> - during record updates (in prepare_update)
> 8. Removed some code for precommitted transactions (was thread-unsafe)
> 9. Fixed errors in ATT_no_cleanup mode
> 10. Changed handling of records changed by transactions in limbo when
> reading them in
> no_rec_version transactions with statement-level read-consistency disabled.
>
> It is possible to split some of the changes into smaller patches, but most
> of the changes depend on each other.
>
> Criticism and suggestions are more than welcome at this stage. The code
> passes some basic testing, but I plan to test it more.
>
> If you like it, and ask me for it, I might actually commit it to HEAD so
> that it is not only me who tests it.
>
> Nikolay Samofatov
>
>
--
Jim Starkey
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