Dear Gerlit,
unfortunately I am not a H2 developper but just an user like you.
However, my company runs several large H2 databases and we operated 15+
GB instances in the past. From this experience, my own observations
are:
1) MVCC has a problem when writing large commits into indexed tables
("write amplification"). Drop the indexes before writing and you will
be fine.
2) At least the latest GIT Snapshot of 2.0.201+ seems to be stable and
I have not been able to corrupt a H2 DB since April this year (related
to the developing H2 code, not related to the H2 user time). Although I
also experience such corruptions with 1.4.200/199. But I was never able
to prove it or to provide reliable test cases, so it is more like an
anecdote.
Please indicate at least, what exact H2 version you are using and also
the exact connection string.
3) I have never used"nioMapped", just plain Single File Access or
Server Mode.
4) I can not confirm your "reads into memory" observation. I was able
to open very large DBs with reasonable small Heaps, but of course only
has long as the Commits are small.
5) not sure, but I believe you still can use PageStore but have to
define it in the connection string and it will be incompatible with
MVCC. I might be wrong on this, have not much interest in it.
Best regards
Andreas
On Wed, 2020-12-23 at 22:19 +0100, Gerlits András wrote:
> Hi all,
>
> I have a rather unique setup in my software where I'm running a
> separate h2 instance for each of my threads. I'm currently running 8
> of them, 2 for each vcpu core. Each of these threads has exclusive
> access to these databases, so they are nice and fast. Because there
> is no parallel access, and because I'm very rarely updating anything
> in these databases, MVCC is not helpful and was measured to be about
> half as performant as pagestore.
>
> So far so good. My problems started when I tried scaling these
> databases to multiple gigabytes each. As soon as I've done that, it
> started corrupting, unless I used "nioMapped". And even then, when I
> open any one of these databases, they are always read into memory
> fully, even if I put "file" in the URL. So, not just in my software,
> but if I open a split database of 2 gigs in a SQL console application
> like squirrel, it grows the amount of used memory by 2 gigabytes or
> throws an out of memory error.
>
> Is there anything obvious I'm doing wrong? I understand that this is
> not something most people do, but I read through what I could before
> posting here and couldn't find anything that says anything in doing
> is wrong.
>
> Any help would be very much appreciated.
>
> Thanks,
> Andras Gerlits
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