[Lustre-devel] Erratum about indexes in robinhood DB

[Lustre-devel] Erratum about indexes in robinhood DB

[Eric Barton]

Thomas,

Thanks a lot and I hope you don't mind me cc-ing lustre-devel as this
seems to be of general interest.

Do you have a feel (or measurements :) for the rate at which a changelog
can be ingested into robinhood?  And I'm wondering about DNE and multiple
changelogs coming from multiple MDTs.  I'd be very interested to know if
you've thought about this and have views on what the maximum ingest rate
could be and whether there will be issues coordinating/merging events
across multiple feeds.

          Cheers,
                   Eric

Eric Barton
CTO Whamcloud, Inc.

> -----Original Message-----
> From: LEIBOVICI Thomas [mailto:thomas.leibovici at cea.fr]
> Sent: 29 September 2011 10:04 AM
> To: Eric Barton
> Subject: Erratum about indexes in robinhood DB
> 
> Hello Eric,
> 
> Re-thinking about your question on indexes in robinhood DB, my answer
> was incomplete.
> Actually, there are indexes on user/group/type/status, but there are not
> on the main table:
> 
> 1) As I said you, on the main table (the one that list all FS entries),
> there are as few indexes as possible (just fid as primary key, and
> parent fid)
> in order to preserve a good insert/update rate on this table whatever
> the FS size (the deeper the DB index trees, the slower those requests).
> 
> 2) There is a secondary table where robinhood maintains aggregated
> statitics like nbr entries, volume per user/group/type/(hsm)status and
> which is updated on the fly.
> This one as indexes on quite all its fields, which makes it possible to
> get instantaneous stats per user, etc. without penalizing insert/update
> rate on main table.
> Indexes on this secondary table are less expensive, given that the set
> of users is much more resticted that the nbr of entries.
> 
> This time you have a more complete answer.
> 
> Best regards
> Thomas

[Lustre-devel] Erratum about indexes in robinhood DB

[LEIBOVICI Thomas]

Hello Eric,

With a fast enough feeder, the ingest rate robinhood can currently 
sustain is between 50.000/sec and 100.000/sec
(depending on insert/update/remove ratio) with a basic MySQL DB stored 
on a local disk.
This can certainly still be improved with MySQL tunings and/or better HW 
and/or enterprise class DB,
but for now, we notice it is easily high enough for reading a MDT 
changelog stream on a Petaflopic system.

This rate is actually lower when processing Lustre MDT changelogs (but I 
have no measurement) because of "stat" operations to get file attributes
(unfortunately, changelogs do not give the new value of what has just 
changed, e.g new uid for a chown operation, new size&mtime with a mtime 
event...)
SOM will probably improve that point, but it could be a good idea to add 
more info in changelogs.

Handling chglogs from multiple MDTs is indeed a very interesting point 
to address.
The main issue is the database scaling in terms of operation rate, 
volume and entry location.
A solution could be using an existing clustered DB engine (MySQL 
cluster, NOSQL DBs...),
thus we are going to take a look at the different alternatives and see 
if they could match the need.
For that, it would be interesting to know how records will be splitted 
into the multiple changelog streams:
is a given fid always reported by the same stream? what about the parent 
fid (like in create/unlink operations)?
If you have a document about DNE design, I think it would give a more 
precise idea about
what event and fid is supposed to be reported by each MDT.

Thanks,
Thomas

Eric Barton wrote:
> Thomas,
>
> Thanks a lot and I hope you don't mind me cc-ing lustre-devel as this
> seems to be of general interest.
>
> Do you have a feel (or measurements :) for the rate at which a changelog
> can be ingested into robinhood?  And I'm wondering about DNE and multiple
> changelogs coming from multiple MDTs.  I'd be very interested to know if
> you've thought about this and have views on what the maximum ingest rate
> could be and whether there will be issues coordinating/merging events
> across multiple feeds.
>
>           Cheers,
>                    Eric
>
> Eric Barton
> CTO Whamcloud, Inc.
>
>   
>> -----Original Message-----
>> From: LEIBOVICI Thomas [mailto:thomas.leibovici at cea.fr]
>> Sent: 29 September 2011 10:04 AM
>> To: Eric Barton
>> Subject: Erratum about indexes in robinhood DB
>>
>> Hello Eric,
>>
>> Re-thinking about your question on indexes in robinhood DB, my answer
>> was incomplete.
>> Actually, there are indexes on user/group/type/status, but there are not
>> on the main table:
>>
>> 1) As I said you, on the main table (the one that list all FS entries),
>> there are as few indexes as possible (just fid as primary key, and
>> parent fid)
>> in order to preserve a good insert/update rate on this table whatever
>> the FS size (the deeper the DB index trees, the slower those requests).
>>
>> 2) There is a secondary table where robinhood maintains aggregated
>> statitics like nbr entries, volume per user/group/type/(hsm)status and
>> which is updated on the fly.
>> This one as indexes on quite all its fields, which makes it possible to
>> get instantaneous stats per user, etc. without penalizing insert/update
>> rate on main table.
>> Indexes on this secondary table are less expensive, given that the set
>> of users is much more resticted that the nbr of entries.
>>
>> This time you have a more complete answer.
>>
>> Best regards
>> Thomas
>>     
>
>   

[Lustre-devel] Erratum about indexes in robinhood DB

[Eric Barton]

Thomas,

Interesting point about changelog entries requiring a 'stat'.

Nathan, what's your take on making changelogs tell you what has
changed - even if only on "easy" changes?

          Cheers,
                   Eric

> -----Original Message-----
> From: LEIBOVICI Thomas [mailto:thomas.leibovici at cea.fr]
> Sent: 06 October 2011 12:02 PM
> To: Eric Barton
> Cc: lustre-devel at lists.lustre.org
> Subject: Re: Erratum about indexes in robinhood DB
> 
> Hello Eric,
> 
> With a fast enough feeder, the ingest rate robinhood can currently
> sustain is between 50.000/sec and 100.000/sec
> (depending on insert/update/remove ratio) with a basic MySQL DB stored
> on a local disk.
> This can certainly still be improved with MySQL tunings and/or better HW
> and/or enterprise class DB,
> but for now, we notice it is easily high enough for reading a MDT
> changelog stream on a Petaflopic system.
> 
> This rate is actually lower when processing Lustre MDT changelogs (but I
> have no measurement) because of "stat" operations to get file attributes
> (unfortunately, changelogs do not give the new value of what has just
> changed, e.g new uid for a chown operation, new size&mtime with a mtime
> event...)
> SOM will probably improve that point, but it could be a good idea to add
> more info in changelogs.
> 
> Handling chglogs from multiple MDTs is indeed a very interesting point
> to address.
> The main issue is the database scaling in terms of operation rate,
> volume and entry location.
> A solution could be using an existing clustered DB engine (MySQL
> cluster, NOSQL DBs...),
> thus we are going to take a look at the different alternatives and see
> if they could match the need.
> For that, it would be interesting to know how records will be splitted
> into the multiple changelog streams:
> is a given fid always reported by the same stream? what about the parent
> fid (like in create/unlink operations)?
> If you have a document about DNE design, I think it would give a more
> precise idea about
> what event and fid is supposed to be reported by each MDT.
> 
> Thanks,
> Thomas
> 
> Eric Barton wrote:
> > Thomas,
> >
> > Thanks a lot and I hope you don't mind me cc-ing lustre-devel as this
> > seems to be of general interest.
> >
> > Do you have a feel (or measurements :) for the rate at which a changelog
> > can be ingested into robinhood?  And I'm wondering about DNE and multiple
> > changelogs coming from multiple MDTs.  I'd be very interested to know if
> > you've thought about this and have views on what the maximum ingest rate
> > could be and whether there will be issues coordinating/merging events
> > across multiple feeds.
> >
> >           Cheers,
> >                    Eric
> >
> > Eric Barton
> > CTO Whamcloud, Inc.
> >
> >
> >> -----Original Message-----
> >> From: LEIBOVICI Thomas [mailto:thomas.leibovici at cea.fr]
> >> Sent: 29 September 2011 10:04 AM
> >> To: Eric Barton
> >> Subject: Erratum about indexes in robinhood DB
> >>
> >> Hello Eric,
> >>
> >> Re-thinking about your question on indexes in robinhood DB, my answer
> >> was incomplete.
> >> Actually, there are indexes on user/group/type/status, but there are not
> >> on the main table:
> >>
> >> 1) As I said you, on the main table (the one that list all FS entries),
> >> there are as few indexes as possible (just fid as primary key, and
> >> parent fid)
> >> in order to preserve a good insert/update rate on this table whatever
> >> the FS size (the deeper the DB index trees, the slower those requests).
> >>
> >> 2) There is a secondary table where robinhood maintains aggregated
> >> statitics like nbr entries, volume per user/group/type/(hsm)status and
> >> which is updated on the fly.
> >> This one as indexes on quite all its fields, which makes it possible to
> >> get instantaneous stats per user, etc. without penalizing insert/update
> >> rate on main table.
> >> Indexes on this secondary table are less expensive, given that the set
> >> of users is much more resticted that the nbr of entries.
> >>
> >> This time you have a more complete answer.
> >>
> >> Best regards
> >> Thomas
> >>
> >
> >

[Lustre-devel] Erratum about indexes in robinhood DB

[Nathan Rutman]

We actually already did some of that for a one-off. We didn't push the changes upstream because
there were some ugly layering violations involved.  Vitaly, do you remember the details?


On Oct 11, 2011, at 6:04 AM, Eric Barton wrote:

> Thomas,
> 
> Interesting point about changelog entries requiring a 'stat'.
> 
> Nathan, what's your take on making changelogs tell you what has
> changed - even if only on "easy" changes?
> 
>         Cheers,
>                  Eric
> 
>> -----Original Message-----
>> From: LEIBOVICI Thomas [mailto:thomas.leibovici at cea.fr]
>> Sent: 06 October 2011 12:02 PM
>> To: Eric Barton
>> Cc: lustre-devel at lists.lustre.org
>> Subject: Re: Erratum about indexes in robinhood DB
>> 
>> Hello Eric,
>> 
>> With a fast enough feeder, the ingest rate robinhood can currently
>> sustain is between 50.000/sec and 100.000/sec
>> (depending on insert/update/remove ratio) with a basic MySQL DB stored
>> on a local disk.
>> This can certainly still be improved with MySQL tunings and/or better HW
>> and/or enterprise class DB,
>> but for now, we notice it is easily high enough for reading a MDT
>> changelog stream on a Petaflopic system.
>> 
>> This rate is actually lower when processing Lustre MDT changelogs (but I
>> have no measurement) because of "stat" operations to get file attributes
>> (unfortunately, changelogs do not give the new value of what has just
>> changed, e.g new uid for a chown operation, new size&mtime with a mtime
>> event...)
>> SOM will probably improve that point, but it could be a good idea to add
>> more info in changelogs.
>> 
>> Handling chglogs from multiple MDTs is indeed a very interesting point
>> to address.
>> The main issue is the database scaling in terms of operation rate,
>> volume and entry location.
>> A solution could be using an existing clustered DB engine (MySQL
>> cluster, NOSQL DBs...),
>> thus we are going to take a look at the different alternatives and see
>> if they could match the need.
>> For that, it would be interesting to know how records will be splitted
>> into the multiple changelog streams:
>> is a given fid always reported by the same stream? what about the parent
>> fid (like in create/unlink operations)?
>> If you have a document about DNE design, I think it would give a more
>> precise idea about
>> what event and fid is supposed to be reported by each MDT.
>> 
>> Thanks,
>> Thomas
>> 
>> Eric Barton wrote:
>>> Thomas,
>>> 
>>> Thanks a lot and I hope you don't mind me cc-ing lustre-devel as this
>>> seems to be of general interest.
>>> 
>>> Do you have a feel (or measurements :) for the rate at which a changelog
>>> can be ingested into robinhood?  And I'm wondering about DNE and multiple
>>> changelogs coming from multiple MDTs.  I'd be very interested to know if
>>> you've thought about this and have views on what the maximum ingest rate
>>> could be and whether there will be issues coordinating/merging events
>>> across multiple feeds.
>>> 
>>>         Cheers,
>>>                  Eric
>>> 
>>> Eric Barton
>>> CTO Whamcloud, Inc.
>>> 
>>> 
>>>> -----Original Message-----
>>>> From: LEIBOVICI Thomas [mailto:thomas.leibovici at cea.fr]
>>>> Sent: 29 September 2011 10:04 AM
>>>> To: Eric Barton
>>>> Subject: Erratum about indexes in robinhood DB
>>>> 
>>>> Hello Eric,
>>>> 
>>>> Re-thinking about your question on indexes in robinhood DB, my answer
>>>> was incomplete.
>>>> Actually, there are indexes on user/group/type/status, but there are not
>>>> on the main table:
>>>> 
>>>> 1) As I said you, on the main table (the one that list all FS entries),
>>>> there are as few indexes as possible (just fid as primary key, and
>>>> parent fid)
>>>> in order to preserve a good insert/update rate on this table whatever
>>>> the FS size (the deeper the DB index trees, the slower those requests).
>>>> 
>>>> 2) There is a secondary table where robinhood maintains aggregated
>>>> statitics like nbr entries, volume per user/group/type/(hsm)status and
>>>> which is updated on the fly.
>>>> This one as indexes on quite all its fields, which makes it possible to
>>>> get instantaneous stats per user, etc. without penalizing insert/update
>>>> rate on main table.
>>>> Indexes on this secondary table are less expensive, given that the set
>>>> of users is much more resticted that the nbr of entries.
>>>> 
>>>> This time you have a more complete answer.
>>>> 
>>>> Best regards
>>>> Thomas
>>>> 
>>> 
>>> 
> 
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[Lustre-devel] Erratum about indexes in robinhood DB

[Vitaly Fertman]

HI,

yes, there is a fixed patch which adds some info to the changelog,
UID, GID, NID. it is not a problem to pack it with other (changed)
inode attributes. not sent upstream because an issue has been 
found which fix has not been landed yet.

On Oct 11, 2011, at 9:12 PM, Nathan Rutman wrote:

> We actually already did some of that for a one-off. We didn't push the changes upstream because
> there were some ugly layering violations involved.  Vitaly, do you remember the details?
> 
> 
> On Oct 11, 2011, at 6:04 AM, Eric Barton wrote:
> 
>> Thomas,
>> 
>> Interesting point about changelog entries requiring a 'stat'.
>> 
>> Nathan, what's your take on making changelogs tell you what has
>> changed - even if only on "easy" changes?
>> 
>>        Cheers,
>>                 Eric
>> 
>>> -----Original Message-----
>>> From: LEIBOVICI Thomas [mailto:thomas.leibovici at cea.fr]
>>> Sent: 06 October 2011 12:02 PM
>>> To: Eric Barton
>>> Cc: lustre-devel at lists.lustre.org
>>> Subject: Re: Erratum about indexes in robinhood DB
>>> 
>>> Hello Eric,
>>> 
>>> With a fast enough feeder, the ingest rate robinhood can currently
>>> sustain is between 50.000/sec and 100.000/sec
>>> (depending on insert/update/remove ratio) with a basic MySQL DB stored
>>> on a local disk.
>>> This can certainly still be improved with MySQL tunings and/or better HW
>>> and/or enterprise class DB,
>>> but for now, we notice it is easily high enough for reading a MDT
>>> changelog stream on a Petaflopic system.
>>> 
>>> This rate is actually lower when processing Lustre MDT changelogs (but I
>>> have no measurement) because of "stat" operations to get file attributes
>>> (unfortunately, changelogs do not give the new value of what has just
>>> changed, e.g new uid for a chown operation, new size&mtime with a mtime
>>> event...)
>>> SOM will probably improve that point, but it could be a good idea to add
>>> more info in changelogs.
>>> 
>>> Handling chglogs from multiple MDTs is indeed a very interesting point
>>> to address.
>>> The main issue is the database scaling in terms of operation rate,
>>> volume and entry location.
>>> A solution could be using an existing clustered DB engine (MySQL
>>> cluster, NOSQL DBs...),
>>> thus we are going to take a look at the different alternatives and see
>>> if they could match the need.
>>> For that, it would be interesting to know how records will be splitted
>>> into the multiple changelog streams:
>>> is a given fid always reported by the same stream? what about the parent
>>> fid (like in create/unlink operations)?
>>> If you have a document about DNE design, I think it would give a more
>>> precise idea about
>>> what event and fid is supposed to be reported by each MDT.
>>> 
>>> Thanks,
>>> Thomas
>>> 
>>> Eric Barton wrote:
>>>> Thomas,
>>>> 
>>>> Thanks a lot and I hope you don't mind me cc-ing lustre-devel as this
>>>> seems to be of general interest.
>>>> 
>>>> Do you have a feel (or measurements :) for the rate at which a changelog
>>>> can be ingested into robinhood?  And I'm wondering about DNE and multiple
>>>> changelogs coming from multiple MDTs.  I'd be very interested to know if
>>>> you've thought about this and have views on what the maximum ingest rate
>>>> could be and whether there will be issues coordinating/merging events
>>>> across multiple feeds.
>>>> 
>>>>        Cheers,
>>>>                 Eric
>>>> 
>>>> Eric Barton
>>>> CTO Whamcloud, Inc.
>>>> 
>>>> 
>>>>> -----Original Message-----
>>>>> From: LEIBOVICI Thomas [mailto:thomas.leibovici at cea.fr]
>>>>> Sent: 29 September 2011 10:04 AM
>>>>> To: Eric Barton
>>>>> Subject: Erratum about indexes in robinhood DB
>>>>> 
>>>>> Hello Eric,
>>>>> 
>>>>> Re-thinking about your question on indexes in robinhood DB, my answer
>>>>> was incomplete.
>>>>> Actually, there are indexes on user/group/type/status, but there are not
>>>>> on the main table:
>>>>> 
>>>>> 1) As I said you, on the main table (the one that list all FS entries),
>>>>> there are as few indexes as possible (just fid as primary key, and
>>>>> parent fid)
>>>>> in order to preserve a good insert/update rate on this table whatever
>>>>> the FS size (the deeper the DB index trees, the slower those requests).
>>>>> 
>>>>> 2) There is a secondary table where robinhood maintains aggregated
>>>>> statitics like nbr entries, volume per user/group/type/(hsm)status and
>>>>> which is updated on the fly.
>>>>> This one as indexes on quite all its fields, which makes it possible to
>>>>> get instantaneous stats per user, etc. without penalizing insert/update
>>>>> rate on main table.
>>>>> Indexes on this secondary table are less expensive, given that the set
>>>>> of users is much more resticted that the nbr of entries.
>>>>> 
>>>>> This time you have a more complete answer.
>>>>> 
>>>>> Best regards
>>>>> Thomas
>>>>> 
>>>> 
>>>> 
>> 

--
Vitaly