9:13 a.m.
Considering that the agent has already hit a major problem where Titan is most likely the
cause, I do see that we need to move away from it.
If we go to the next option (Sqlg), how difficult would it be to be able to switch
backends (embedded H2 versus external Postgres)?
And how bad would it be to just support H2 for single-node Hawkular Services installations
(even if in production)?
I don't think we'd want to try to cluster H2 DBs (is that even possible?) in the
case of a multi-node H-Services deployment, but for simple deployments, why make people
install and manage a separate Postgres backend if we can avoid it? But still have the
option to let the person use Postgres if they want.
Obviously, for when running in MiQ environments, we could point inventory to MiQ's
Postgres DB (and that's most likely the vast majority of production deployments - if
not all of them). But for dev environments, I wonder if being able to use the embedded H2
DB would be easier.
In any event, we do need to move off of Titan soon - I can't merge this until we do
(or we fix Titan) - https://github.com/hawkular/hawkular-agent/pull/249
----- Original Message -----
I discussed some more with Lukas and looked around a bit.
Titan is basically the link between TinkerPop (graph API) and Cassandra.
I may have jumped in conclusion but:
- Datastax (the company behind Cassandra) bought ThinkAurelius (the company
behind Titan)
- Since then Datastax built a product "inspired by Titan", a graph DB with
TinkerPop and Cassandra. TThe product is closed-source and completely
targeted to Cassandra. Datastax has no real incentive to maintain Titian as
it competes with their product and all engineers stopped contributing to it.
- Last release of Titan was in Sept 2015 (they used to release ~ every 3
months)
- While the community is relatively active, no Pull request was approved
after June, and we don't know about any fork that is well maintained
- It's a fairly large and complex piece of code, too large and too narrowed
for us to take over.
Conclusion: medium/long term Titan is no longer an option.
The other concern is that there is no good solution to store to Cassandra
which is the only storage dependence for Hawkular Services today (and was an
important requirement).
So we have to make a difficult choice here but we don't seem to have many
options if we stick with TinkerPop at least...
According to Lukas, Sqlg is a good option for the following reasons:
- Performance
- Size/complexity
- The "community" is really small but the lead developer is responsive (and
in the case he stops, it would be easier to fork and maintain).
The big drawback is that for production we would require Postgres (for
non-prod or for Hawkular Services users who don't use the inventory service,
we can use the embedded H2).
Thoughts ?
Thomas
On Thu, Jul 21, 2016 at 2:08 PM, Lukas Krejci < lkrejci(a)redhat.com > wrote:
Hi all,
to move inventory forward, we need to port it to Tinkerpop3 - a new(ish) and
actively maintained version of the Tinkerpop graph API.
Apart from the huge improvement in the API expressiveness and capabilities,
the important thing is that it comes with a variety of backends, 2 of which
are of particular interest to us ATM. The Titan backend (with Titan in
version
1.0) and SQL backend (using the sqlg library).
The SQL backend is a much improved (yet still unfinished in terms of
optimizations and some corner case features) version of the toy SQL backend
for Tinkerpop2.
Back in March I ran performance comparisons for SQL/postgres and Titan
(0.5.4)
on Tinkerpop2 and concluded that Titan was the best choice then.
After completing a simplistic port of inventory to Tinkerpop3 (not taking
advantage of any new features or opportunities to simplify inventory
codebase), I've run the performance tests again for the 2 new backends -
Titan
1.0 and Sqlg (on postgres).
This time the results are not so clear as the last time.
>From the charts [1] you can see that Postgres is actually quite a bit faster
on reads and can better handle concurrent read access while Titan shines in
writes (arguably thanks to Cassandra as its storage).
Of course, I can imagine that the read performance advantage of Postgres
would
decrease with the growing amount of data stored (the tests ran with the
inventory size of ~10k entities) but I am quite positive we'd get competitive
read performance from both solutions up to the sizes of inventory we
anticipate (100k-1M entities).
Now the question is whether the insert performance is something we should be
worried about in Postgres too much. IMHO, there should be some room for
improvement in Sqlg and also our move to /sync for agent synchronization
would
make this less of a problem (because there would be not that many initial
imports that would create vast amounts of entities).
Nevertheless I currently cannot say who is the "winner" here. Each backend
has
its pros and cons:
Titan:
Pros:
- high write throughput
- backed by cassandra
Cons:
- slower reads
- project virtually dead
- complex codebase (self-made fixes unlikely)
Sqlg:
Pros:
- small codebase
- everybody knows SQL
- faster reads
- faster concurrent reads
Cons:
- slow writes
- another backend needed (Postgres)
Therefore my intention here is to go forward with a "proper" port to
Tinkerpop3 with Titan still enabled but focus primarily on Sqlg to see if we
can do anything with the write performance.
IMHO, any choice we make is "workable" as it is even today but we need to
weigh in the productization requirements. For those Sqlg with its small dep
footprint and postgres backend seems preferable to the huge dependency mess
of
Titan.
[1] https://dashboards.ly/ua-TtqrpCXcQ3fnjezP5phKhc
--
Lukas Krejci
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