Weird Path in Git directory Structure -

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i have seen following path in directory of .git.

.git/object/3b/12abef878787483abeceddaa5544489abff789a

when infact sha 3b12abef878787483abeceddaa5544489abff789a

which sha of contents of file , hence should stored without /. why did git store blob in weird path,what advantages of doing so?

the reason prevent there being many files in 1 directory. sha values start 3b stored in sub-directory 3b, workload on single directory 1/256th of if blobs in single directory. ultimately, speeds performance; there less searching find particular blob.

you can see similar effects in terminfo directory, entries sub-divided directories based on first letter of terminal entry. cpan system has authors/id/a/aa/aardvark in naming hierarchy.

please elaborate little bit me.

suppose git wants find blob 3b12abef878787483abeceddaa5544489abff789a , directory partitioning scheme not in use. there might be, sake of argument, 512 blobs, , file, kernel might have read 512 directory entries in .git/objects find right entry.

now suppose directory partitioning scheme in use, , miracle of statistical mischance, there 256 subdirectories each containing 2 files. kernel @ worst has read 256 directory entries 2-byte names in each entry (compared 512 directory entries 32-byte names) in ./git/objects directory, , has read @ worst 2 entries 30-byte names in ./git/objects/3b directory.

there complicating factors, such imperfectly balanced hashing , memory caching , disk accesses, general idea distributing files multiple subdirectories means os kernel has less work find file. if number of files in directory extend multiple hundreds, worth considering breaking down.


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