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3274f58948
* Summay
This revision includes big change about temporary file and local cache file.
By this big change, s3fs works with good performance when s3fs opens/
closes/syncs/reads object.
I made a big change about the handling about temporary file and local cache
file to do this implementation.
* Detail
1) About temporary file(local file)
s3fs uses a temporary file on local file system when s3fs does download/
upload/open/seek object on S3.
After this revision, s3fs calls ftruncate() function when s3fs makes the
temporary file.
In this way s3fs can set a file size of precisely length without downloading.
(Notice - ftruncate function is for XSI-compliant systems, so that possibly
you have a problem on non-XSI-compliant systems.)
By this change, s3fs can download a part of a object by requesting with
"Range" http header. It seems like downloading by each block unit.
The default block(part) size is 50MB, it is caused the result which is default
parallel requests count(5) by default multipart upload size(10MB).
If you need to change this block size, you can change by new option
"fd_page_size". This option can take from 1MB(1024 * 1024) to any bytes.
So that, you have to take care about that fdcache.cpp(and fdcache.h) were
changed a lot.
2) About local cache
Local cache files which are in directory specified by "use_cache" option do
not have always all of object data.
This cause is that s3fs uses ftruncate function and reads(writes) each block
unit of a temporary file.
s3fs manages each block unit's status which are "downloaded area" or "not".
For this status, s3fs makes new temporary file in cache directory which is
specified by "use_cache" option. This status files is in a directory which is
named "<use_cache sirectory>/.<bucket_name>/".
When s3fs opens this status file, s3fs locks this file for exclusive control by
calling flock function. You need to take care about this, the status files can
not be laid on network drive(like NFS).
This revision changes about file open mode, s3fs always opens a local cache
file and each status file with writable mode.
Last, this revision adds new option "del_cache", this option means that s3fs
deletes all local cache file when s3fs starts and exits.
3) Uploading
When s3fs writes data to file descriptor through FUSE request, old s3fs
revision downloads all of the object. But new revision does not download all,
it downloads only small percial area(some block units) including writing data
area.
And when s3fs closes or flushes the file descriptor, s3fs downloads other area
which is not downloaded from server. After that, s3fs uploads all of data.
Already r456 revision has parallel upload function, then this revision with
r456 and r457 are very big change for performance.
4) Downloading
By changing a temporary file and a local cache file, when s3fs downloads a
object, it downloads only the required range(some block units).
And s3fs downloads units by parallel GET request, it is same as a case of
uploading. (Maximum parallel request count and each download size are
specified same parameters for uploading.)
In the new revision, when s3fs opens file, s3fs returns file descriptor soon.
Because s3fs only opens(makes) the file descriptor with no downloading
data. And when s3fs reads a data, s3fs downloads only some block unit
including specified area.
This result is good for performance.
5) Changes option name
The option "parallel_upload" which added at r456 is changed to new option
name as "parallel_count". This reason is this option value is not only used by
uploading object, but a uploading object also uses this option. (For a while,
you can use old option name "parallel_upload" for compatibility.)
git-svn-id: http://s3fs.googlecode.com/svn/trunk@458 df820570-a93a-0410-bd06-b72b767a4274
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