Hi Thomas,
Thanks for the clarification.
What happens when MVCC is on and a user sets the transaction isolation
to something other than read committed?
Thanks,
Gili
On 27/11/2013 2:22 PM, Thomas Mueller wrote:
Hi,
When MVCC is disabled, see
http://h2database.com/html/advanced.html#transaction_isolation
When MVCC is enabled, then H2 behaves in the same way as with read
committed. At least currently. In the future this may change. See also
http://h2database.com/html/advanced.html#mvcc for details
Regards,
Thomas
Thomas,
I just want to make sure that you don't lose track of this question
(since you replied to a follow-up discussion): what is the difference
between SERIALIZABLE isolation when MVCC is on or off?
Thanks,
Gili
On Sunday, November 24, 2013 10:50:18 AM UTC-5, Gili wrote:
Hi Thomas,
It was my understanding that SERIALIZABLE isolation in MVCC mode
is supposed to behave like SERIALIZABLE_SNAPSHOT. At least, that's
the case for Postgres. If SERIALIZABLE behaves the way you mention
in MVCC mode, what is the difference if MVCC mode is on or off? It
doesn't sound like there is a difference.
Gili
On 24/11/2013 7:49 AM, Thomas Mueller wrote:
Hi,
> How does SERIALIZABLE isolation in MVCC mode compare to
SERIALIZABLE_SNAPSHOT? Aren't they the same thing?
I can only refer to Google, which found this:
http://blogs.msdn.com/b/craigfr/archive/2007/05/16/serializable-vs-snapshot-isolation-level.aspx
<http://www.google.com/url?q=http%3A%2F%2Fblogs.msdn.com%2Fb%2Fcraigfr%2Farchive%2F2007%2F05%2F16%2Fserializable-vs-snapshot-isolation-level.aspx&sa=D&sntz=1&usg=AFQjCNHL8riZ1UQ_8q-_ir8sxbV5VX7_XQ>
Regards,
Thomas
On Sun, Nov 24, 2013 at 1:10 PM, cowwoc <[email protected]
<mailto:[email protected]>> wrote:
Hi Thomas,
Thanks for the reply.
On 21/11/2013 6:43 AM, Thomas Mueller wrote:
>Does H2 implement Serializable Snapshot
Currently not, and I didn't plan to support it. In theory,
it could be supported with the MVStore, but I don't
currently think it's very important.
How does SERIALIZABLE isolation in MVCC mode compare to
SERIALIZABLE_SNAPSHOT? Aren't they the same thing?
Thanks,
Gili
Regards,
Thomas
On Sat, Aug 24, 2013 at 8:10 PM, Gili
<[email protected] <mailto:[email protected]>>
wrote:
Thomas,
Can you please clarify how H2's implementation of MVCC
interacts with Transaction Isolation?
1. Is there a practical difference between
READ_COMMITTED and REPEATABLE_READ in MVCC mode?
Doesn't MVCC prevent READ_COMMITTED from seeing
updates committed by other transactions (after the
current transaction has already read the row once)?
If so, aren't they identical?
2. Same question for REPEATABLE_READ and SERIALIZABLE
isolation in MVCC mode.
3. Does H2 implement
http://en.wikipedia.org/wiki/Serializable_Snapshot_Isolation#Serializable_Snapshot_Isolation
<http://www.google.com/url?q=http%3A%2F%2Fen.wikipedia.org%2Fwiki%2FSerializable_Snapshot_Isolation%23Serializable_Snapshot_Isolation&sa=D&sntz=1&usg=AFQjCNExhEdVr75dgDxP5G40R7fHvGul7A>
for
MVCC? If not, do you plan on doing so in the future?
Thank you,
Gili
On Sunday, June 23, 2013 11:23:16 AM UTC-4, Gili wrote:
Thanks Thomas. So you're saying I can use other
isolation modes with MVCC as I normally would?
Gili
On 23/06/2013 7:39 AM, Thomas Mueller wrote:
Hi,
H2 only supports row level locks when using the
MVCC mode. By the way, the plan is that in the
future (with the MVStore), the MVCC mode will be
the default mode.
Insert/delete operations don't wait for other
operations that do not conflict. They wait for
conflicting operations (changes on the same rows).
> What happens in the following scenario?
H2 uses "read committed" by default, so T1 will see
the value from T2.
Regards,
Thomas
On Thu, Jun 20, 2013 at 8:18 PM, Gili
<[email protected]
<mailto:[email protected]>> wrote:
Hi,
Looking at
http://www.h2database.com/html/advanced.html#mvcc
<http://www.google.com/url?q=http%3A%2F%2Fwww.h2database.com%2Fhtml%2Fadvanced.html%23mvcc&sa=D&sntz=1&usg=AFQjCNEZaGOPQsTGn9GcPhWhhmbHy_80kw>,
1. Does H2 only support table locks or MVCC?
Or is there a way to get row locks without
MVCC?
2. Using MVCC, do insert/delete operations
wait until all open transactions complete?
3. Does this imply that open transactions will
never experience insert/delete rows by
other threads in mid-transaction?
4. What happens in the following scenario?
Database contains a single row: count[value=1]
T1: Open transaction
T2: Open transaction
T2: update count set value=2 where value=1
T2: commit
T1: select value from count
Will T1 see a value of 1 or 2?
Thanks,
Gili
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