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In the mean time, the master branch evolved quite a bit and the schema
changed again (eqclass added to function table). The main reason for the
merge is to resolve the large amounts of conflicts once, so development
of the sqlalchemy branch can continue and still benefit from changes in
the master branch such as schema compatibility, adapting the indent
level in web app due to the use of contextlib.closing which resembles
sqlalchemy's "with db.begin() as conn:".
Conflicts:
autoimport.py
dedup/utils.py
readyaml.py
update_sharing.py
webapp.py
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Hash functions are partitioned into equivalence classes. We are
generally only interested in sharing among hash functions with the same
equivalence class, but the algorithm would compute any sharing. While
the current layout never produces the same hashes for functions in
difference equivalence classes (for different output length), that may
change in future.
Also allow hash functions, that belong to no equivalence class at all
(eqclass = NULL) as a means to add additional metadata to content
without computing any sharing for it.
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This makes the sqlalchemy branch schema-compatible with master again.
The biggest change on master was the introduction of the function table.
It caused most of the conflicts. Note that webapp had one conflict not
detected by git: The selecting of issues in show_package needed
sqlalchemy conversion.
Conflicts:
README
update_sharing.py
webapp.py
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* Rename "image_sha512" to "png_sha512".
* dedup.image.ImageHash is now a base class for image hashes such as
PNGHash and GIFHash.
* Enable both hashes in importpkg.
* Fix README.
* Add new hash combinations to webapp.
* Add "gif file not named *.gif" to issues in update_sharing.
* Add redirect for "image_sha512" to webapp for backwards
compatibility.
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Actual savings on the full data set are around 7%.
Conflicts:
README
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Currently this is invalid .gz files and png files not named .png.
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This already worked quite well for package.id. On a test data set of 5%
size this transformation reduces the database size by about 4%.
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Without using this wrapper the sql statements are not munged by
sqlalchemy. Specifically paramstyle is not translated. For sqlite3 this
did not matter, because it allows the changed paramstyle, but for
postgres it fails without sqlalchemy.text wrappers.
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This basically pulls the packageid branch into sqlalchemy. The merge was
complex, because many sql statements diverged. The merge brings us one
step closer to supporting postgres, because an "INSERT OR REPLACE" was
removed from readyaml.py in the packageid branch.
Conflicts:
update_sharing.py
webapp.py
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By using the :name syntax inside sql statements, sqlalchemy will replace
the contents with whatever paramstyle the underlying dbapi2 module
needs. In case of psycopg2 the paramstyle is not qmark for instance.
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One approach to improve performance is to reduce the database size. A
package name takes up 15 bytes in average. A number of a package takes
up two bytes. Multiply that difference with the number of references and
it should be noticeably. A small test set show a reduction by 10%.
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Makes usage of sqlalchemy easier, cause I can invoke it once and it
works for all connections.
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The original version had two major drawbacks:
1) The SQL query used would cause a btree sort, so the time waiting
for the first output was rather long.
2) For packages with many equal files, the output would grow with
O(n^2).
Thanks to the suggestions by Christine Grohne and Klaus Aehlig. The
approach now groups files in package1 by their main hash value (sha512).
It also does some work SQL was designed to solve manually now. To speed
up page generation a new caching table was added identifying which files
have corresponding shared files.
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In the old content table (package, filename, size) would be the same for
multiple hash functions. Now the schema represents that each file has
precisely one size, but multiple hashes.
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The sharing table is a cache for the /binary web pages. It essentially
contains the numbers presented. This caching table is not automatically
populated. It needs to be reconstructed after every (group of) package
imports.
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