[GitHub] [arrow] westonpace commented on issue #35305: [C++] Support predicate pushdown for timestamp and string types in Parquet Scanner

["westonpace (via GitHub)" <gi...@apache.org>]

westonpace commented on issue #35305:
URL: https://github.com/apache/arrow/issues/35305#issuecomment-1527954990

   I think we might need more details or a reproducing script of some kind.  Here is a quick experiment I ran:
   
   ```
   import pyarrow as pa
   import pyarrow.compute as pc
   import pyarrow.parquet as pq
   import pyarrow.dataset as ds
   import shutil
   
   shutil.rmtree("/tmp/my_dataset", ignore_errors=True)
   
   values = list(range(100))
   
   int_col = pa.array(values, pa.int64())
   ts_col = pc.cast(int_col, pa.timestamp('us'))
   
   table = pa.Table.from_arrays([int_col, ts_col], names=["ints","timestamps"])
   
   ds.write_dataset(table, "/tmp/my_dataset", format="parquet")
   
   my_dataset = ds.dataset("/tmp/my_dataset")
   
   # Prime the query once to load parquet metadata into memory                                                                                                                                                        
   my_dataset.to_table()
   
   big_ts = pc.cast(pa.array([1000], pa.int64()), pa.timestamp('us'))[0]
   print("WITH FILTER")
   print(my_dataset.to_table(filter=pc.field("timestamps") > big_ts))
   
   print("WITHOUT FILTER")
   print(my_dataset.to_table())
   ```
   
   I then tested this with `strace` using the command `strace -f -P /tmp/my_dataset/part-0.parquet python repr.py`:
   
   ```
   WITH FILTER
   pyarrow.Table
   ints: int64
   timestamps: timestamp[us]
   ----
   ints: [[]]
   timestamps: [[]]
   WITHOUT FILTER
   [pid 43296] openat(AT_FDCWD, "/tmp/my_dataset/part-0.parquet", O_RDONLY) = 7
   [pid 43296] newfstatat(7, "", {st_mode=S_IFREG|0664, st_size=2111, ...}, AT_EMPTY_PATH) = 0
   [pid 43296] newfstatat(7, "", {st_mode=S_IFREG|0664, st_size=2111, ...}, AT_EMPTY_PATH) = 0
   [pid 43314] pread64(7, "\25\4\25\300\f\25\266\6L\25\310\1\25\4\22\0\0\240\6\0\0\r\1\0\1\r\10\0\2\r\10\0"..., 595, 4) = 595
   [pid 43314] pread64(7, "\25\4\25\300\f\25\266\6L\25\310\1\25\4\22\0\0\240\6\0\0\r\1\0\1\r\10\0\2\r\10\0"..., 595, 695) = 595
   [pid 43314] close(7)                    = 0
   pyarrow.Table
   ints: int64
   timestamps: timestamp[us]
   ----
   ints: [[0,1,2,3,4,...,95,96,97,98,99]]
   timestamps: [[1970-01-01 00:00:00.000000,1970-01-01 00:00:00.000001,1970-01-01 00:00:00.000002,1970-01-01 00:00:00.000003,1970-01-01 00:00:00.000004,...,1970-01-01 00:00:00.000095,1970-01-01 00:00:00.000096,1970-01-01 00:00:00.000097,1970-01-01 00:00:00.000098,1970-01-01 00:00:00.000099]]
   ```
   
   I also verified with a debugger that the row groups are not actually being read.
   
   


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