[ovs-dev] [PATCH] ovsdb-idl: Re-parse backrefs of inserted rows only once.

Ilya Maximets i.maximets at ovn.org
Fri Nov 19 17:42:08 UTC 2021

On 11/19/21 12:02, Dumitru Ceara wrote:
> Hi Ilya,
> On 11/19/21 3:22 AM, Ilya Maximets wrote:
>> While adding new rows ovsdb-idl re-parses all the other rows that
>> references this new one.  For example, current ovn-kubernetes creates
>> load balancers and adds the same load balancer to all logical switches
>> and logical routers.  So, then a new load balancer is added, rows for
>> all logical switches and routers re-parsed.
>> During initial database connection (or re-connection with
>> monitor/monitor_cond or moniotr_cond_since with outdated last
> Typo: moniotr.
>> transaction id) the client downloads the whole content of a database.
>> In case of OVN, there might be already thousands of load balancers
>> configured.  ovsdb-idl will process rows in that initial monitor reply
>> one-by-one.  Therefore, for each load balancer row, it will re-parse
>> all rows for switches and routers.
>> Assuming that we have 120 Logical Switches and 30K load balancers.
>> Processing of the initial monitor reply will take 120 (switch rows) *
>> 30K (load balancer references in a switch row) * 30K (load balancer
>> rows) = 10^11 operations, which may take hours.
> Well, as mentioned in other discussions, the application should use Load
> Balancer groups in that case but if it can not, or for the Southbound
> database case where the contents are 120 Datapath_Binding records each
> referring to 30K load balancer UUIDs, this patch is very beneficial.
>> Re-parsing doesn't change any internal structures of the IDL.  It
>> destroys and re-creates exactly same arcs between rows.  The only
>> thing that changes is the application-facing array of pointers.
>> Since internal structures remains intact, suggested solution is to
>> postpone the re-parsing of back references until all the monitor
>> updates processed.  This way we can re-parse each row only once.
> Cool!
>> Tested in a sandbox with 120 LSs, 120 LRs and 3K LBs, where each
>> load balancer added to each LS and LR, by re-statring ovn-northd and
>> measuring the time spent in ovsdb_idl_run().
>> Before the change:
>>   OVN_Southbound: ovsdb_idl_run took: 924 ms
>>   OVN_Northbound: ovsdb_idl_run took: 825118 ms  --> 13.75 minutes!
>> After:
>>   OVN_Southbound: ovsdb_idl_run took: 692 ms
>>   OVN_Northbound: ovsdb_idl_run took: 1698 ms
> I confirm; I also see signficant improvement when running against NB/SB
> databases taken from an OpenShift large scale cluster.
>> Signed-off-by: Ilya Maximets <i.maximets at ovn.org>
>> ---
> The code looks good to me, thanks!
> Acked-by: Dumitru Ceara <dceara at redhat.com>

Thanks!  I adjusted the commit message and applied.

Best regards, Ilya Maximets.

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