[Webkit-unassigned] [Bug 97570] New: IndexedDB: Allow multiple transactions to run in parallel

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=97570

           Summary: IndexedDB: Allow multiple transactions to run in
                    parallel
           Product: WebKit
           Version: 523.x (Safari 3)
          Platform: Unspecified
        OS/Version: Unspecified
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: WebCore Misc.
        AssignedTo: webkit-unassigned at lists.webkit.org
        ReportedBy: jsbell at chromium.org
        Depends on: 97501


Per spec http://dvcs.w3.org/hg/IndexedDB/raw-file/tip/Overview.html#transaction-concept transactions within a database can run in parallel:

* a version change transaction precludes all other transactions
* "readonly" transactions can run at the same time even if their scopes are overlapping
* multiple "readwrite" transactions can't run at the same time if their scopes are overlapping

More details in the spec about letting readonly and readwrite transactions run in parallel - basically, transactions should read from a data snapshot so that their view of data is consistent.

Following webkit.org/b/97501 WebKit runs transactions serially within a database. Allowing read-only transactions to run in parallel will be a nice performance boost. We can do this incrementally:

(1) Allow transactions with non-overlapping scopes to run in parallel
(2) Allow read-only transactions with overlapping scopes to run in parallel
(3) Give each transaction a "snapshot" of the database, and only serialize read-write transactions with overlapping scopes

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