u3Izx9ql7vW4 commented on issue #43929:
URL: https://github.com/apache/arrow/issues/43929#issuecomment-2325536409
That's correct, I'm writing to IPC with memory mapped files. I did go over
the page you linked a few times but couldn't figure out the difference between
`new_file` and `new_stream`, as they both accept `NativeFile` . I needed to
have multiple IPCs streams running, so I opted for memory mapped files which
allowed me to designate a file path for each producer. Could this be done with
Arrows' memory buffer somehow?
> If you just want to write to disk and keep the file memory mapped it's
likely easier (and faster) to just write an arrow file to disk and mmap it
after.
I don't quite follow this part. Isn't this what I'm already doing? Perhaps
you're suggesting that I check if the mem map file has already been created
before creating a new one, like below?
```python
def save_data():
size = table.get_total_buffer_size()
file_path = os.path.join(prefix_stream, sink)
if not os.path.exists(file_path):
pa.create_memory_map(file_path, size)
with pa.memory_map(file_path, 'wb') as sink:
with pa.ipc.new_file(sink, table.schema) as writer:
writer.write_table(table, max_chunksize=1000)
```
> edit: actually the offset is likely metadata, maybe?
That's what I thought as well, but I would have thought the
`total_buffer_size` would have included the metadata. Though I may have
dictionary encoded columns, so maybe that's inflating the metadata. Do you know
if there's a way to find out?
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