[BDB 11gR2 Beta] Berkeley DB 11gR2 Beta release -- Mike Owens [#18275]

[Dave Segleau]

Michael/Alex,

Can you comment on Mike Owen's observations and questions below?

Thanks,

Dave

On 3/20/2010 8:01 PM, Mike Owens wrote:
> I should have the article ready by next Monday 29th. I've got my test 
> code together and have some things that I am not quite clear on.
>
> I guess the relates to both the article and the tech eval. I can't 
> quite figure out what PRAGMA synchronous means in BDB. This is an 
> important comparison and when I run some benchmarks I get better 
> performance with synchronous=1 than with synchronous=0 in BDB, which 
> is counterintuitive with SQLite.
>
> I see some comments in sql/adaptor/btree.c that suggest that perhaps 
> the numbers don't mean the same things:
>
> /*
> ** Change the way data is synced to disk in order to increase or 
> decrease how
> ** well the database resists damage due to OS crashes and power failures.
> ** Level 1 is the same as asynchronous (no syncs() occur and there is 
> a high
> ** probability of damage)  Level 2 is the default.  There is a very 
> low but
> ** non-zero probability of damage.  Level 3 reduces the probability of 
> damage
> ** to near zero but with a write performance reduction.
> **
> ** Berkeley DB always does the equivalent of "fullSync".
> */
> int sqlite3BtreeSetSafetyLevel(Btree *p, int level, int fullSync)
> {
>     BtShared *pBt;
>     log_msg(LOG_VERBOSE,
>         "sqlite3BtreeSetSafetyLevel(%p, %u, %u)", p, level, fullSync);
>
>     pBt = p->pBt;
>     if (GET_DURABLE(p->pBt)) {
>         pDbEnv->set_flags(pDbEnv, DB_TXN_NOSYNC, (level == 1));
>         pDbEnv->set_flags(pDbEnv, DB_TXN_WRITE_NOSYNC, (level == 2));
>     }
>     return SQLITE_OK;
> }
>
> For SQLite levels, 0=OFF, 1=NORMAL, 2=FULL (there is no 3).
>
> In the code above, it seems that 1=OFF and 2=NORMAL and I don't see 
> any code that sets FULL (unless this is 3 in BDB and equates to the 
> default "fullSync").
>
> The BDB code that parses this PRAGMA is identical to SQLite's (in 
> sqlite/src/pragma.c which both code bases share identically) in that 
> it associates whatever integer value is passed in through SQL is 
> associated with the DB/btree.
>
> The problem here is that if this is true, then BDB's values are 
> different from SQLite's. And if a programmer were going for SQLite's 
> synchronous value of 1, it would mean that the sme code running 
> against BDB would not be durable (nosyncs) -- something they would not 
> expect.
>
> Can you confirm this for me?
>
> If this is true, then perhaps the above code should be (in part)
>
>    if (GET_DURABLE(p->pBt)) {
>         pDbEnv->set_flags(pDbEnv, DB_TXN_NOSYNC, (level == 0));
>         pDbEnv->set_flags(pDbEnv, DB_TXN_WRITE_NOSYNC, (level == 1));
>     }
>
> And at least 0 and 1 would match up with SQLite. Still not sure about 
> 2 (unless again it maps to BDB's level which is default fullSync).
>
> Thanks,
>
> Mike
>
> On Fri, Mar 19, 2010 at 1:54 PM, Dave Segleau <dave.segleau at oracle.com 
> <mailto:dave.segleau at oracle.com>> wrote:
>
>     Hello Mike,
>
>     Thank you very much for the quote earlier this week.
>
>     I wanted to let you know that the final Beta Release snapshot is
>     now available here:
>
>     http://download.oracle.com/otn/beta/bdb/db-5.0.13.zip
>     http://download.oracle.com/otn/beta/bdb/db-5.0.13.tar.gz
>
>     This is the last planned Berkeley DB 11gR2 beta snapshot. This
>     snapshot contains bug fixes, documentation updates and a cleaned
>     up build process. We're on target for a production release on
>     March 31st. Please provide any feedback or major issues by end of
>     day, Monday March 22nd.
>
>     I'm looking forward to seeing your article. When do to you think
>     that you'll have a draft.
>
>     Also, I'm working with Jonathan to get OSCON on "marketing
>     program" map. Is there anyone at OSCON that I can speak with to
>     get an understanding of typical attendance and profile of the
>     attendees?
>
>     Thank you very much for your participation in the Beta program.
>     Your evaluation and feedback about the product is very valuable to
>     us.
>
>     Regards,
>
>     Dave
>

-- 
Oracle <http://www.oracle.com>
David Segleau | Director Product Management - Berkeley DB
Phone: +1 425 945 8533 | Mobile: +1 408 420 7350
Oracle Database Engineering

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