Hi Stefan,
Just wanted to add some info to Ivan's answer.
First of all, about this blocking thing. This is more like internal
stuff, but if you're comfortable with database locking, you'll
understand what I'm saying. Since one of the transactions was reading
'$documents' system doc, it blocked the whole database in read mode.
Then another transaction wanted to write something and started to wait
for write-lock. That's why new session couldn't get in: it started to
wait in the locking queue. However, for me it's still a mystery why this
first transaction hadn't finished. It seems that it was waiting for
another lock, which should have given us a deadlock, but it didn't. If
you could send older parts of the event log, that would definitely help.
About read-only transactions. Ivan already told you about "-upd-crt".
That's true: this is the parameter. However, notice that we use static
snapshots for read-only transactions. That means every time we want to
make new data available for read-only transactions, there will be a
short barrier-like synchronization that will stall the whole processing.
You can try to set the parameter to '0' and see if that works for you.
In this case snapshots will be advanced after any transaction with
updates commits. Or you can set it to a (very) small value. There is no
"rule-of-thumb" here. Try increasing the value from '0' until you're
satisfied with the performance of your workload.
---
Alex Kalinin
Sedna Team
On 02/22/11 11:22, Stefan Koch wrote:
Hi Ivan,
I've attached a log from today where I had to stop the database,
because everything was blocked. It occured at 11:39.
Se Version is 3.4.66 64 bit (binaryversion), OS is OpenSuse 10.3 64 bit.
I've tested a bit with readonly mode, it works but it only finds
pretty old data. it couldn't even find something that I created 20
minutes before, for much older data it worked fine.
Do you know how bit this gap is?
Greetings from Berlin
Stefan
Am 21.02.2011 14:06, schrieb Ivan Shcheklein:
Stefan,
Try driver from the latest Sedna build
http://modis.ispras.ru/FTPContent/sedna/development/ . It contains
call to enable/disable read-only mode.
Ivan
On Sat, Feb 19, 2011 at 3:33 PM, Ivan Shcheklein
<[email protected] <mailto:[email protected]>> wrote:
Stefan,
@logs, I'll have to look them up, but there is nothing in
there, sedna just hangs and after 2 minutes the log is
updated. Probably the default log-level is not ideal for
this, but as already said it's an productive environment.
Anyway, can you share it with us? (you can remove any valuable
information from queries (save only names of
documents/collections and send directly to the sedna at ispras.ru
<http://ispras.ru>). Default log-level should be enough. BTW,
what version of Sedna do you use (number, x86/x64, OS)?
Does this mean if you don't use collections at all, the lock
is just for single documents and not for the entire collection?
Yes, exactly. But stand-alone documents introduce some other
penalties - you can't create index over multiple documents, you
can't query them with one XPath, they don't share internal
structures so that it's not possible to load millions of
documents without collection.
We use collection to organize different clients (customers),
we do not have to this, but it's very convenient for
administrative purposes to have all clients in different
collections and in one database instance and some clients
have multiple collections.
Sounds reasonable, and anyway I don't see straightforward
explanation for 20-30 seconds hangs in your current system.
@Java-API Update ASAP - that's very great to hear! We've
already written a C JNI wrapper, but coming from a high level
language like Java C is a pain in the ass ;) I don't want to
push you, your support has always been awesome and fast, but
can you say how long it will take, until you update the Java
API? It's just for us to know if we keep on fighting with the
obstacles of C, or if we wait to the next update.
Couple of days I believe.
@Benchmarks: When I do them, I will post my results here!
Ok.
Ivan Shcheklein,
Sedna Team
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