<div dir="ltr">Comments inline.<br><br><div><div class="gmail_extra"><div class="gmail_quote">On Mon, Dec 19, 2016 at 1:47 PM, Xavier Hernandez <span dir="ltr"><<a href="mailto:xhernandez@datalab.es" target="_blank">xhernandez@datalab.es</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div class="HOEnZb"><div class="h5">On 12/19/2016 07:57 AM, Aravinda wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<br>
regards<br>
Aravinda<br>
<br>
On 12/16/2016 05:47 PM, Xavier Hernandez wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
On 12/16/2016 08:31 AM, Aravinda wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
Proposal to add one more byte to GFID to store "Type" information.<br>
Extra byte will represent type(directory: 00, file: 01, Symlink: 02<br>
etc)<br>
<br>
For example, if a directory GFID is f4f18c02-0360-4cdc-8c00-0164e4<wbr>9a7afd<br>
then, GFID2 will be 00f4f18c02-0360-4cdc-8c00-0164<wbr>e49a7afd.<br>
<br>
Changes to Backend store<br>
------------------------<br>
Existing: .glusterfs/gfid[0:2]/gfid/[2:4<wbr>]/gfid<br>
Proposed: .glusterfs/gfid2[0:2]/gfid2[2:<wbr>4]/gfid2[4:6]/gfid2<br>
<br>
Advantages:<br>
-----------<br>
- Automatic grouping in .glusterfs directory based on file Type.<br>
- Easy identification of Type by looking at GFID in logs/status output<br>
etc.<br></blockquote></blockquote></blockquote></div></div></blockquote><div><br></div><div>Above two will be good enough points to bump up the priority for the feature.<br> <br></div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div class="HOEnZb"><div class="h5"><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
- Crawling(Quota/AFR): List of directories can be easily fetched by<br>
crawling `.glusterfs/gfid2[0:2]/` directory. This enables easy<br>
parallel Crawling.<br></blockquote></blockquote></blockquote></div></div></blockquote><div><br></div><div>With the current design, we still have to do a distributed readdir() to get all <br>the entries in the directory. This layout change, along with proposed <br>DHT2/EHT/DHT2+ (name for me doesn't matter here) layout, where directory <br>entries would be created in just one place should enhance the performance overall.<br></div><div> </div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div class="HOEnZb"><div class="h5"><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
- Quota - Marker: Marker transator can mark xtime of current file and<br>
parent directory. No need to update xtime xattr of all directories<br>
till root.<br>
- Geo-replication: - Crawl can be multithreaded during initial sync.<br>
With marker changes above it will be more effective in crawling.<br>
<br></blockquote></blockquote></blockquote></div></div></blockquote><div> </div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div class="HOEnZb"><div class="h5"><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
Please add if any more advantageous.<br>
<br>
Disadvantageous:<br>
----------------<br>
Functionality is not changed with the above change except the length<br>
of the ID. I can't think of any disadvantages except the code changes<br>
to accommodate this change. Let me know if I missed anything here.<br>
</blockquote>
<br>
One disadvantage is that 17 bytes is a very ugly number for<br>
structures. Compilers will add paddings that will make any structure<br>
containing a GFID noticeable bigger. This will also cause troubles on<br>
all binary formats where a GFID is used, making them incompatible. One<br>
clear case of this is the XDR encoding of the gluster protocol.<br>
Currently a GFID is defined this way in many places:<br>
<br>
opaque gfid[16]<br>
<br>
This seems to make it quite complex to allow a mix of gluster versions<br>
in the same cluster (for example in a middle of an upgrade).<br></blockquote></blockquote></div></div></blockquote><div><br></div><div>Totally agree with Xavier here. Not in support of adding one more byte.<br> <br></div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div class="HOEnZb"><div class="h5"><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<br>
What about this alternative approach:<br>
<br>
Based on the RFC4122 [1] that describes the format of an UUID, we can<br>
define a new structure for new GFID's using the same length.<br>
<br>
Currently all GFID's are generated using the "random" method. This<br>
means that all GFID have this structure:<br>
<br>
xxxxxxxx-xxxx-Mxxx-Nxxx-xxxxxx<wbr>xxxxxx<br>
<br>
Where N can be 8, 9, A or B, and M is 4.<br>
<br>
There are some special GFID's that have a M=0 and N=0, for example the<br>
root GFID.<br>
<br>
What I propose is to use a new variant of GFID, for example E or F<br>
(officially marked as reserved for future definition) or even 0 to 7.<br>
We could use M as an internal version for the GFID structure (defined<br>
by ourselves when needed). Then we could use the first 4 or 8 bits of<br>
each GFID as you propose, without needing to extend current GFID<br>
length nor risking to collide with existing GFID's.<br>
<br>
If we are concerned about the collision probability (quite small but<br>
still bigger than the current version) because we loose some random<br>
bits, we could use N = 0..7 and leave M random. This way we get 5 more<br>
random bits, from which we could use 4 to represent the inode type.<br>
<br>
I think this way everything will work smoothly with older versions<br>
with minimal effort.<br>
<br>
What do you think ?<br>
</blockquote>
That is really nice suggestion.<br>
<br>
To get the crawling advantageous as mentioned above, we need to make<br>
backend store as .glusterfs/N/gfid[0:2]/gfid[2:<wbr>4]/gfid<br>
</blockquote>
<br></div></div>
That's one possibility. Since N will be 4 bits at most, it won't collide with currently existing subdirectories that represent 8 bits. Or we could use M. It all depends on the exact interpretation we give to each field.<br>
<br>
One suggestion I would make is to define it in a way that we use the minimal amount of bits to represent what we need now but leave space for future extensions. For example creating a "reserved" value for the field.<br>
<br>
Proposal:<br>
<br>
Use N = 00xx for special GFID's, like NULL GFID, or the ones currently used in some places. All these will also have M = 0. All other values of M will be reserved for future extensions.<br>
<br>
Also reserve all other values of N (01xx) for future extensions.<br>
<br>
This gives a lot of space to represent many things in the future if necessary, while keeping current usage compatible with it.<br>
<br>
For this particular case we could use N = 0000 and define M as (this is a mapping of the posix S_IFxxx values):<br>
<br>
M = 0000 Current special GFID's<br>
M = 0001 Fifo (S_IFIFO)<br>
M = 0010 Character Device (S_IFCHR)<br>
M = 0100 Directory (S_IFDIR)<br>
M = 0110 Block Device (S_IFBLK)<br>
M = 1000 Regular File (S_IFREG)<br>
M = 1010 Symbolic Link (S_IFLNK)<br>
M = 1100 Socket (S_IFSOCK)<br>
<br>
M = xx11 \<br>
M = x1x1 | Reserved for future extensions<br>
M = 1xx1 |<br>
M = 111x /<br>
<br>
If we use our own mapping instead of using the same values than IF_Sxxx macros, we can get a more compact representation if needed.<br>
<br>
In this case the directory structure could be .glusterfs/M/gfid[0:2]/gfid[2:<wbr>4]/gfid. And use M = 0 to put all current existing gfid's, or we could leave existing gfid's in their current location.<br>
<br>
Or we could even have .glusterfs/NM/gfid[0:2]/gfid[2<wbr>:4]/gfid. This would probably be compatible even with future extensions.<br>
<br></blockquote><div><br></div><div>I would go with only 'M' being considered for current layout and keeping N for future developments. Even though we are not considering 'N' internally, we can keep directory name as '00MM' (zero zero M M). so that backend layout would be compatible to consider N later if required.<br><br></div><div>One major thing is we need a solid plan for migration from current layout to newer layout.<br><br></div><div>Regards,<br></div><div>Amar<br> <br></div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
Xavi<div class="HOEnZb"><div class="h5"><br>
<br>
<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<br>
Xavi<br>
<br>
[1] <a href="https://www.ietf.org/rfc/rfc4122.txt" rel="noreferrer" target="_blank">https://www.ietf.org/rfc/rfc41<wbr>22.txt</a><br>
<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<br>
Changes:<br>
---------<br>
- Code changes to accommodate 17 bytes GFID instead of 16 bytes(Read<br>
and Write)<br>
- Migration Tool to upgrade GFIDs in Volume/Cluster<br>
<br>
Let me know your thoughts.<br>
<br>
</blockquote>
<br>
</blockquote>
<br>
</blockquote>
<br>
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