> I'd appreciate it if anyone could let me know if this pragma still
> works and how to use it if so.
You can get away without pragma. Just implement your own VFS which
will redirect all calls except lock-related to the standard VFS.
Lock-related methods would be implemented as no-op and thus won't
cause any performance problems.
Pavel
On Thu, Feb 17, 2011 at 4:36 PM, Mike Lin <m...@mit.edu> wrote:
> Dear all,
>
> I have a large SQLite database with genomic data which is strictly
> read-only at this point, and in direct spite of the FAQ I intend to
> query it concurrently on a network FS. Our parallel FS ought to be
> able to handle a heavy read workload from our cluster, based on past
> experience, but acquiring read locks seems to cause a bottleneck. I
> have found a few mentions of an experimental 'pragma omit_readlock'
> which seems just right for this situation, but I have not been having
> luck making it work so far.
>
> I also found the following June 2009 e-mail to this list from Joerg
> Hoinkis that seemed to make some progress by digging into the SQLite
> source, but did not get any replies. I have similarly tried some
> obvious things like opening my database with SQLITE_OPEN_READONLY and
> making sure my file's permissions are 444.
>
> I'd appreciate it if anyone could let me know if this pragma still
> works and how to use it if so.
>
> Thanks,
> Mike Lin
>
>
>> Hi!
>>
>> I'm trying to access a readonly database without locks, using the
>> amalgamation of SQLite 3.6.14.2
>>
>> After I opened the database with flags = SQLITE_OPEN_READONLY I perform
>>
>> sqlite3_exec (db, "PRAGMA omit_readlock=ON", 0, 0, 0);
>>
>> I traced that down into the amalgamation to the point where the database
>
>> flag is set in flagPragma...
>>
>> db->flags |= p-mask;
>>
>> So I can be sure the pragma syntax is correct.
>>
>>
>> Now when I execute a SELECT statement, it is parsed and I run into
>> pagerSharedLock, but
>> the pager->noReadlock variable is 0. As a result the database file gets
>> locked.
>>
>>
>> It look like the initialization of the pager->noReadlock flag, but that
>> happens when the database is
>> opened.
>
> I messed up the last sentence, better:
>
> It looks like the initialization of the pager->noReadlock flag only
> happens
> when the database is opened, but by that time the omit_readlock pragma is
> not active.
>
>>
>> Am I doing something wrong or did this ("Very experimental") feature got
>
>> lost in past refactorings?
>>
>>
>> Thanks for listening & in advance to any hints
>
> Joerg
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>
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