So far I've been thinking of this topos SHM htable stuff as a replacement for existing storages (redis/mysql).

Now, I am thinking of this topos SHM htable as a cache between kama procs and existing storages. So this should happen:
1. on store, always keep in shm htable and write in storage db
2. on load, check shm htable first, and if not found, load from storage db in shm htable

Should be an improvement to existing active-active setups, when redis db becomes unavailable.

Of course, DMQ sync of this topos SHM htable can be done, in best effort way. Can happen that db storage is unavailable and DMQ sync is too slow at the same time => topos will still fail.

Thanks,
Stefan

On Mon, Oct 21, 2024 at 4:28 PM Stefan Mititelu <stefan.mititelu@net2phone.com> wrote:
Hi,

Thanks for the feedback for this.

My motivation is related to an active-active scenario and supposing that redis db becomes unavailable => topology info will then become unavailable. Now that I am double thinking about DMQ sync, I think you are right. If DMQ does not sync fast enough, there will be no topology info available too...

Looking in existing code, and doing some tests with redis, I see topos does 2 types of redis store:
1. for dialog "d:..."
2. for each transaction "b:..."

I. Suppose a BYE comes to a kamailio => topos needs to have the nr 1. already synced or will send back "404 Not here" and not forward the BYE
II. Suppose a 200OK for that BYE comes to a diiferent kamailio => topos needs to have the nr 2. already synced or will have bad Via header and log error

Thank you,
Stefan 

On Mon, Oct 21, 2024 at 10:02 AM Henning Westerholt <hw@gilawa.com> wrote:

Hi Stefan,

 

certainly, a new storage mode “shared memory” could be added, to avoid any additional dependencies for topos. This sounds useful.

 

I personally don’t see a large case for adding also DMQ synchronisation capabilities for it. The DMQ synchronisation is not 100% reliable in all corner cases, there are no locks or other synchronization mechanism implemented. As a loss of topology related information would cause immediate issues for message processing, it might be not the best choice especially as there is already redis as a distributed in memory storage available.

 

But maybe I just misunderstood the motivation for the DMQ synchronization for topos information. If its e.g. more about an active/passive fail-over setup, data-consistency issues are of course not a big issue.

 

Cheers,

 

Henning

 

 

From: Stefan Mititelu via sr-dev <sr-dev@lists.kamailio.org>
Sent: Friday, October 18, 2024 10:45 AM
To: sr-dev@lists.kamailio.org
Cc: Stefan Mititelu <stefan.mititelu@net2phone.com>
Subject: [sr-dev] topos module with storage "shm"

 

Hi,

I am thinking of this idea to add shm storage for topos module. Main motivation for this is that if db backend is not available, there will be no store/load happening.

Did anyone else thought of this or is doing something similar already?

I see 2 milestones here:

1. Add code in topos to keep a shm hash table with all the information needed, guarded via locks. The api functions should be very similar to what tps_storage.c has, just it will do ops directly in memory not on db.

2. Find a way to synchronize this topos hash table among multiple kamailios. This should be similar to how htable module syncronize via DMQ. Sync may happen either for each new cell, for batches or for entire topos hash table.

What do you think of this? Any opinions, comments, appreciated.

Thank you,

Stefan Mititelu