[Lustre-devel] rename in Changelog

[Lai Siyao]

Mike, you're right, only rename needs to use the new version of changelog
format; and
it will be unpacked in liblustreapi, the user space tool will not even
notice it.

On Thu, Apr 26, 2012 at 2:06 AM, Mikhail Pershin <mike.tappro at gmail.com>wrote:

> On Wed, 25 Apr 2012 20:36:08 +0400, Nathan Rutman <
> Nathan_Rutman at xyratex.com> wrote:
>
>  it wasn't done that way in the first place because the record size in an
>> llog is fixed,
>> so any size increase is multiplied by the number of records, so fewer
>> records
>> can be stored.  Splitting the rename into two was the unfortunate
>> casualty of that goal.
>>
>
> This is true if we are using the same record for all operations and Lai
> did so by adding extra field. But I'd note that fixed size is not mandatory
> thing but good to have. Moreover, changelog records are naturally not fixed
> size because contain name which size is not fixed. So I suppose rename was
> done in two parts just as simpler way to go because required no additional
> changes in processing, etc. Also, IIRC, CL_EXT appeared even later than
> CL_RENAME itself.
>
> To avoid space consuming we can just introduce extended
> 'changelog_ext_rec' for rename. It is not the problem to create such
> changelogs but requires processing tools to be aware about that, is that a
> big problem or acceptable?
>
>
>
>> On Apr 25, 2012, at 2:05 AM, Lai Siyao wrote:
>>
>>  Rename record in Changelog is different from other operations, it's
>>> split into
>>> two records: RNMFRM and RNMTO. This makes Changelog analysis hard
>>> because these two records may not be consecutive and several renames
>>> may occur at the same time.
>>>
>>> I'm not clear why it's designed to be so, except that RNMTO is needed
>>> because for DNE (distributed namespace) the rename target may reside on
>>> another MDS, and a separate RNMTO record is needed. But even with this
>>> it's fine to store all information in a RENME record, but leave the
>>> information of
>>> whether rename removes the last hardlink of the target file (if it
>>> exists) in
>>> RNMTO record.
>>>
>>> I tried to add a field spfid in struct changelog_rec to store source
>>> parent fid,
>>> and pack both source (if has) and target names into record. Normally the
>>> record size if sizeof(fid) larger than before, and it can be
>>> differentiated
>>> according to version. The test result looks good, but I want to know
>>> whether
>>> anyone oppose to this? If not, I'll make the change and make it changelog
>>> version 2.
>>>
>>> Cheers,
>>> - Lai
>>>
>>>
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