I am going to look into the following dev idea:
1. from htable module try export a bind() API functions (e.g. similar to
usrloc) and check that basic htable module ops can be done from another
module
2. next, create a topos_htable module that will work with those htable
module API functions
3. last, add new storage("htable") to topos module
This way, topos can use all features of htable module (e.g. standalone SHM
storage and DMQ sync if/when needed)
Thanks,
Stefan
On Tue, Oct 22, 2024 at 10:07 AM Henning Westerholt <h...@gilawa.com> wrote:
> Hi Stefan,
>
>
>
> thanks for the reply. DMQ is usually fast, but it can have data loss or
> data synchronization issues if you are using in concurrent access scenarios.
>
>
>
> Regarding using the shared memory as a cache, this is of course frequently
> used in usrloc module or others. It would certainly help for short
> unavailability of the database. It also should improve the performance if
> combined with a timer-based write-back mode, like in usrloc.
>
>
>
> Cheers,
>
>
>
> Henning
>
>
>
> *From:* Stefan Mititelu <stefan.mitit...@net2phone.com>
> *Sent:* Monday, October 21, 2024 5:05 PM
> *To:* Henning Westerholt <h...@gilawa.com>
> *Cc:* Kamailio (SER) - Development Mailing List <sr-dev@lists.kamailio.org
> >
> *Subject:* Re: [sr-dev] topos module with storage "shm"
>
>
>
> 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.mitit...@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 <h...@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.mitit...@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
>
>
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