Merge 35947d5 into e1d16fe

.gitignore

@@ -313,3 +313,6 @@ third_party/gflags/
 
 # Test output file logs to ignore
 stats_log
+
+test.txt
+Vagrantfile

CodeReview#1_README.md

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+## Files Added
+
+* [compressed_tile.cpp](https://github.com/rohit-cmu/compression-peloton/blob/master/src/storage/compressed_tile.cpp)
+* [compressed_tile.h](https://github.com/rohit-cmu/compression-peloton/blob/master/src/include/storage/compressed_tile.h)
+
+### Other Existing Files Modified
+
+Some additional functions have been added to support database compression. Here are the following files:
+
+* [tile.h](https://github.com/rohit-cmu/compression-peloton/blob/master/src/include/storage/tile.h)
+* [tile.cpp](https://github.com/rohit-cmu/compression-peloton/blob/master/src/storage/tile.cpp)
+* [tile_group.h](https://github.com/rohit-cmu/compression-peloton/blob/master/src/include/storage/tile_group.h)
+* [tile_group.cpp](https://github.com/rohit-cmu/compression-peloton/blob/master/src/storage/tile_group.cpp)
+* [data_table.cpp](https://github.com/rohit-cmu/compression-peloton/blob/master/src/storage/data_table.cpp)
+
+
+## Strategy for Compressing
+
+* Once a tile gets full (all slots occupied by tuples), the CompressTile is created.
+* We scan each column and sort it.
+* We compute the median, min and max, this gives us the minoffset(min-median) and maxoffset(max-median).
+* If these offsets can be represented in a smaller data type than the original data type, we compress the entire column.
+* The median is chosen as the base, and essentially only the offsets are stored in the column.
+* Currently we can compress SMALLINT and INTEGER and BIGINT. TINYINT is already 1 byte so we do not compress it.
+* We are yet to add support for decimal values.
+* This median is also stored as the metadata to later retrieve the original value
+
+## Testing
+
+* [Compression Correctness Test](https://github.com/rohit-cmu/compression-peloton/blob/master/test/sql/compression_sql_test.cpp)
+* [Compression Size Test](https://github.com/rohit-cmu/compression-peloton/blob/master/test/storage/compression_test.cpp)
+
+
+### Compression Correctness Test:
+* This test inserts 25 tuples
+* Each tuple is of the form (i, i*100) where i belongs to (0,25)
+* Since each tile group contains 1 tile and 10 tuples per tile, there are 3 tile groups formed.
+* The first 2 tile groups are full and get compressed.
+* The third tile group has 5 slots vacant and is still not full and is uncompressed.
+* Thus we now have compressed and uncompressed data.
+* We now perform a SELECT * on this and expect to correctly recieve the true value of the compressed data and uncompressed data.
+
+### Compression Size Test:
+* This test inserts 100 tuples
+* Each tuple is of the form [Integer, Integer, Decimal, Varchar]
+* Thus the tuple length is (4+ 4+ 8+ 8) = 24 bytes.
+* We currently support the compression of integers
+* The integers get compressed to TINYINT making the tuple sizes now (1+ 1+ 8+ 8) = 18 bytes
+* The test checks this decrease in size.
+
+
+
+