389-devel February 2019

389-devel@lists.fedoraproject.org

9 participants
28 discussions

[discuss] Entry cache and backend txn plugin problems
by Mark Reynolds 05 Mar '19

05 Mar '19

I want to start a brief discussion about a major problem we have backend transaction plugins and the entry caches. I'm finding that when we get into a nested state of be txn plugins and one of the later plugins that is called fails then while we don't commit the disk changes (they are aborted/rolled back) we DO keep the entry cache changes! For example, a modrdn operation triggers the referential integrity plugin which renames the member attribute in some group and changes that group's entry cache entry, but then later on the memberOf plugin fails for some reason. The database transaction is aborted, but the entry cache changes that RI plugin did are still present :-( I have also found other entry cache issues with modrdn and BE TXN plugins, and we know of other currently non-reproducible entry cache crashes as well related to mishandling of cache entries after failed operations. It's time to rework how we use the entry cache. We basically need a transaction style caching mechanism - we should not commit any entry cache changes until the original operation is fully successful. Unfortunately the way the entry cache is currently designed and used it will be a major change to try to change it. William wrote up this doc: http://www.port389.org/docs/389ds/design/cache_redesign.html But this also does not currently cover the nested plugin scenario either (not yet). I do know how how difficult it would be to implement William's proposal, or how difficult it would be to incorporate the txn style caching into his design. What kind of time frame could this even be implemented in? William what are your thoughts? If William's design is too huge of a change that will take too long to safely implement then perhaps we need to look into revising the existing cache design where we use "cache_add_tentative" style functions and only apply them at the end of the op. This is also not a trivial change. And what impact would changing the entry cache have on Ludwig's plugable backend work? Anyway we need to start thinking about redesigning the entry cache - no matter what approach we want to take. If anyone has any ideas or comments please share them, but I think due to the severity of this flaw redesigning the entry cache should be one of our next major goals in DS (1.4.1?). Thanks, Mark

4 7

Please review
by Anuj Borah 28 Feb '19

28 Feb '19

Hi all, Please review bellow PR: https://pagure.io/389-ds-base/pull-request/50178 Its pending from long time . Regards Anuj Borah

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Fwd: Filter does not work with Anonymous connection
by Anuj Borah 27 Feb '19

27 Feb '19

Hi all, We have recently implemented Filter and Anonymous to lib389 . But it seems like Filter does not work with Anonymous connection . It actually does not work with any kind of connection whether ACI allow or not rather than root . My suspense is it is related to this issue which is not yet fixed: https://pagure.io/389-ds-base/issue/50137 Please check attached test case . Regards Anuj Borah

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Re: [discuss] Entry cache and backend txn plugin problems
by Howard Chu 27 Feb '19

27 Feb '19

> Date: Tue, 26 Feb 2019 17:21:50 -0700 > From: Rich Megginson <rmeggins(a)redhat.com> > Message-ID: <d40bde83-1e88-b34f-9b5d-d2b320468f14(a)redhat.com> > On 2/26/19 4:26 PM, William Brown wrote: >>> I think the recursive/nested transaction on the database level are not the problem, we do this correctly already, either all or no change becomes persistent. >>> What we do not manage is modifications we do in parallel on the in memory structure like the entry cache, changes to the EC are not managed by any txn and I do not see how any of the database txn models would help, they do not know about ec and can abort changes. >>> We would need to incorporate the EC into a generic txn model, or have a way to flag ec entries as garbage for if a txn is aborted >> The issue is we allow parallel writes, which breaks the consistency guarantees of the EC anyway. LMDB won’t allow parallel writes (it’s single write - concurrent parallel readers), and most other modern kv stores take this approach too, so we should be remodelling our transactions to match this IMO. It will make the process of how we reason about the EC much much simpler I think. > Some sort of in-memory data structure with fast lookup and transactional semantics (modify operations are stored as mvcc/cow so each read of the database with a given txn handle sees its own > view of the ec, a txn commit updates the parent txn ec view, or the global ec view if no parent, from the copy, a txn abort deletes the txn's copy of the ec) is needed. A quick google search > turns up several hits. I'm not sure if the B+Tree proposed at http://www.port389.org/docs/389ds/design/cache_redesign.html has transactional semantics, or if such code could be added to its > implementation. > > With LMDB, if we could make the on-disk entry representation the same as the in-memory entry representation, then we could use LMDB as the entry cache too - the database would be the entry > cache as well. Exactly. This was the original design goal for back-mdb and LMDB in OpenLDAP. http://www.openldap.org/lists/openldap-devel/200905/msg00036.html Note that the back-mdb in OpenLDAP 2.4 is a compromise from this original design; we still have a slight deserialization pass when reading entries from the DB. But it's much simpler and faster than what we used to do with back-bdb/hdb. Ultimately - if your local persistence layer is so slow that it needs an in-memory cache, that local persistence layer is broken. This conclusion is inescapable, after many years of working with BerkeleyDB. -- -- Howard Chu CTO, Symas Corp. http://www.symas.com Director, Highland Sun http://highlandsun.com/hyc/ Chief Architect, OpenLDAP http://www.openldap.org/project/

1 0

Please review: 50230 - improve permission error messages
by William Brown 27 Feb '19

27 Feb '19

https://pagure.io/389-ds-base/pull-request/50248 https://pagure.io/389-ds-base/issue/50230 -- Sincerely, William

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Pagure broken?
by William Brown 27 Feb '19

27 Feb '19

I did a merge for a PR, and now everything on pagure seems to have locked up? I don’t know what’s the next step to investigate or resolve this issue, but it looks like most git-related web UI actions are frozen for now. :( — Sincerely, William Brown Software Engineer, 389 Directory Server SUSE Labs

1 1

please review: PR 50216 - UI - implement Database tab in reactJS
by Mark Reynolds 26 Feb '19

26 Feb '19

https://pagure.io/389-ds-base/pull-request/50216

1 1

Please review 50137 create exist check
by William Brown 26 Feb '19

26 Feb '19

https://pagure.io/389-ds-base/issue/50137 https://pagure.io/389-ds-base/pull-request/50245 — Sincerely, William Brown Software Engineer, 389 Directory Server SUSE Labs

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Please review: 50243 add modrdn refint test
by William Brown 25 Feb '19

25 Feb '19

https://pagure.io/389-ds-base/issue/50243 https://pagure.io/389-ds-base/pull-request/50244 -- Sincerely, William

1 0

Please Review: 50242 fix lib389 list issue
by William Brown 25 Feb '19

25 Feb '19

https://pagure.io/389-ds-base/pull-request/50242 — Sincerely, William Brown Software Engineer, 389 Directory Server SUSE Labs

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389-devel February 2019