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Re: (ITS#6716) syncprov sessionlog 'sl_mincsn' not assigned a value.
- To: openldap-its@OpenLDAP.org
- Subject: Re: (ITS#6716) syncprov sessionlog 'sl_mincsn' not assigned a value.
- From: firstname.lastname@example.org
- Date: Thu, 20 Jan 2011 23:21:49 GMT
- Auto-submitted: auto-generated (OpenLDAP-ITS)
Chris Mikkelson wrote:
> On Thu, Jan 13, 2011 at 12:30:32PM -0800, Howard Chu wrote:
>> email@example.com wrote:
>>> Other than the patch I suggested (using the list head's
>>> CSN value directly), I can think of two other approaches:
>>> 1) When adding an entry to the sessionlog, check
>>> if sl_mincsn is empty. If it is, update sl_mincsn
>>> to the new entry's CSN.
>>> 2) When initializing the sessionlog, set sl_mincsn
>>> to the maximum contextCSN value of the underlying
>>> #2 seems ideal from an efficiency standpoint, although it
>>> differs from the algorithm the current code appears to be
>>> intended to implement.
>> We should have gone with #2. The problem scenario:
> The current code (in HEAD) covers the vast majority of
> cases, but still has a hole which can come up quite often
> in MMR + refreshOnly scenarios. The scenario:
> 1: provider 1, provider 2, and consumer all in sync. SID 1 CSN
> is a few minutes old, SID 2 is a few hours old. Both sessionlogs
> are empty with sl_mincsn set to the newest (provider 1) CSN value
> 2: stop consumer
> 3: write on provider 2
> 4: start consumer
> The provider will see that the consumer is out of date
> wrt the SID 2 CSN and that the old value of the SID 2 CSN
> predates sl_mincsn, so it will skip the session log.
> I think the following approach will cover this case:
> * sl_mincsn holds a CSN value for each SID
Yeah, looks like we were headed there anyway.
> * in syncprov_op_search, mincsn is compared to
> the sl_mincsn value with the same SID
The mincsn variable is no longer useful as-is. We need to compare the vector
of CSNs from the cookie with the vector of CSNs in the provider. If any CSN in
the consumer is older than the matching sl_mincsn then the log must be skipped.
At this point there are a bunch of redundant O(N^2) walkthrus of the CSNs
anyway, so getting rid of mincsn would be a good simplification. Since there
may be many SIDs it would be better to sort both vectors and then walk thru
> * when expiring log entries in in syncprov_add_slog,
> the sl_mincsn value with the same SID as the expired
> entry's CSN is set to the maximum of the two values.
> If there is no matching SID in sl_mincsn, then:
> * in syncprov_op_search, this implies that the
> mincsn's SID has been added to the provider's
> configuration since startup or that the first
> change recorded by that SID occurred since startup,
> and thus the sessionlog contains sufficient
> * in syncprov_add_slog, sl_mincsn will need to
> be expanded to hold the new SID's CSN
-- Howard Chu
CTO, Symas Corp. http://www.symas.com
Director, Highland Sun http://highlandsun.com/hyc/
Chief Architect, OpenLDAP http://www.openldap.org/project/