On 4/1/22 13:28, Dumitru Ceara wrote:
> On 3/29/22 11:40, Dumitru Ceara wrote:
>> OVS commit 1cc618c32524 ("ovsdb-idl: Fix atomicity of writes that
>> don't change a column's value.") [0] explains why writes that don't
>> change a column's value cannot be optimized out early if the column is
>> read/write.
>>
>> In northd, most tables have change tracking enabled, making all their
>> columns read/write. That means that a write to a column (even if it
>> doesn't change the value) will add the row to the current transaction.
>> Validation is eventually performed before sending the transaction to the
>> server but if there are lots of such records this becomes costly.
>>
>> Profiling what happens in northd when running with a NB database taken
>> from an ovn-k8s-like scale test (16K load balancers applied to 120
>> logical switches and routers) we notice that ovn-northd was always
>> writing to the SB.Load_Balancer columns even if nothing changed.
>>
>> This commit changes that behavior and only writes to the
>> SB.Load_Balancer columns if needed.
>>
>> Without this change, in our test server, with ovn-northd running
>> against NB database mentioned above, processing loop intervals were
>> ~13 seconds.
>>
>> With this change applied, loop intervals go down to ~7 seconds.
>>
>> [0] https://github.com/openvswitch/ovs/commit/1cc618c32524
>>
>> Reported-at: https://bugzilla.redhat.com/show_bug.cgi?id=2069623
>> Signed-off-by: Dumitru Ceara <[email protected]>
>> ---
Also, just for future reference, the regression was introduced when
change tracking of the SB database was enabled:
Fixes: e4d6d3455baf ("ovn-northd: Enable change tracking for all SB tables.")
>
> Please disregard this patch.
>
> A more generic solution is proposed at the IDL layer:
>
> https://patchwork.ozlabs.org/project/openvswitch/list/?series=293071&state=*
>
> Once that is accepted we can instead just change ovn-northd to call:
>
> ovsdb_idl_track_changes_noalert(sb_idl);
>
> Regards,
> Dumitru
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