Re: [sqlite] legacy_file_format

[Mark Richards]

That's the problem!  Thank you for pointing it out.

/m

[EMAIL PROTECTED] wrote:
Version 3.3.7 creates (by default) a database file that can be read or 
written by any version of SQLite back to version 3.0.0.  There is no

need to do the "PRAGMA legacy_file_format=ON".  That is now the default.

But you are trying to read the database with SQLite version 2.8.17,
which is earlier (and vastly different) from version 3.0.0.
--
D. Richard Hipp   <[EMAIL PROTECTED]>



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Re: [sqlite] Is it possible to call sqlite_exec() from within the callback made inside sqlite_exec()

[drh]

Kevin Stewart <[EMAIL PROTECTED]> wrote:
> I am still curious. Generally speaking, can one access
> the database inside the callback from select via sqlite_exec()?
> 

Yes.  SQLite is reentrant.

SQLite uses this reentrancy internally.  There are occasions
when you are running an SQL statement that SQLite while invoke
sqlite3_exec() as part of the processing for that SQL statement.
This happens, for example, when you are running an ALTER TABLE
or a CREATE TABLE command.

--
D. Richard Hipp   <[EMAIL PROTECTED]>


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[sqlite] Query Optimisation Question?

[Da Martian]

Hi

I have found that using an in clause with a subquery can be twice as fast as
a straght join. Can enyone explain the logic of this to me? I am curious to
understand it so I can optimise other queries for better performance.

I have included the queries below:

OT_TARGETS has 20 rows for regionid = 1
OT_PRODUCTS has 201 rows for regionid = 1

select distinct RegionID, ProductID, ProductName,  ProductShortName,
ProductRank
from
  OT_PRODUCTS p
Where
  RegionID = 1  and
  ProductID in (select distinct productid from ot_targets where regionid =
1)
order by
  ProductRank,
  ProductName,
  ProductID;

2-3 seconds slower than above:

select distinct t.RegionID, t.ProductID, p.ProductName,  p.ProductShortName,
p.ProductRank
from
OT_TARGETS t,
OT_PRODUCTS p
Where
   t.ProductID = p.ProductID and
   t.RegionID = p.RegionID and
   t.RegionID = 1
 order by
  p.ProductRank,
  p.ProductName,
  p.ProductID;


Thanks,

Re: [sqlite] Is it possible to call sqlite_exec() from within the callback made inside sqlite_exec()

[Jay Sprenkle]

On 9/15/06, Kevin Stewart <[EMAIL PROTECTED]> wrote:

Well, its a little more complicated than that. I don't want the whole
table, just the set of records that matched the initial search criteria
in the select. But thanks for your response. I did a little redesigning


Add a where clause to the select statement that is the source for the
insert.


of the database schema and the way my code handles things and I came up
with a better solution anyway. Maybe I shouldn't have jumped the gun and
submitted this questionhowever I am still curious. Generally
speaking, can one access the database inside the callback from select
via sqlite_exec()?


I believe not.

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Re: [sqlite] Concurrency with writer and read-only processes

[Thomas . L]

On Fri, 15 Sep 2006 17:29:13 -0400, you wrote:

Hi Liam

>I have a database that has one writer which runs once a day, and
>potentially many readers running whenever someone wants some
>information.  I am trying to understand concurrency in sqlite3 so that

I do a daily Job too in my programm. It seems to me, there are
likewise rules.

If you allow reading while another Process do a big writing, several
reader possible get different results, while writer is not ready.
Thats not a Sqlite-Problem, its the same to all other DB.

The better way is, to lock the Table while it is be  written and allow
reading then, if this Jobs is ready.
I don't mean a read-write-dialog-process in this case , but a big
writer, ideally a  especially and exclusive writer.

Reading isn't a primary concurrency problem, much more writing is.

I do my big writing while the system is generally locked to possible
1500 users. It's customized to a time, when Users are not present - at
03:00 o'clock in the morning.

>I understand from lang_transaction that if the writer starts with
>BEGIN IMMEDIATE
>and ends with
>END
>then it will be possible for readers to read the database while the
>writer is updating it: 

Is it ok to you, that user possibly get different or premature
Query-Results?


Best Regards
Thomas

www.thlu.de

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