This blog post provides some context on why you might use this.
You can fetch a version built for Ubuntu 16.04 at https://s3.amazonaws.com/cldellow/public/libparquet/libparquet.so.xz
The first run will git clone a bunch of libraries, patch them to be statically linkable and build them.
Subsequent builds will only build the parquet virtual table extension.
./make-linux-pgo to build an instrumented binary, run tests to collect real-life usage samples, then build an optimized binary. PGO seems to give a 5-10% reduction in query times.
$ sqlite/sqlite3 sqlite> .load build/linux/libparquet sqlite> CREATE VIRTUAL TABLE demo USING parquet('parquet-generator/99-rows-1.parquet'); sqlite> SELECT * FROM demo; ...if all goes well, you'll see data here!...
Note: if you get an error like:
sqlite> .load build/linux/libparquet Error: parquet/libparquet.so: wrong ELF class: ELFCLASS64
You have the 32-bit SQLite installed. To fix this, do:
sudo apt-get remove --purge sqlite3 sudo apt-get install sqlite3:amd64
Row group filtering
Row group filtering is supported for strings and numerics so long as the SQLite type matches the Parquet type.
e.g. if you have a column
foo that is an INT32, this query will skip row groups whose
statistics prove that it does not contain relevant rows:
SELECT * FROM tbl WHERE foo = 123;
but this query will devolve to a table scan:
SELECT * FROM tbl WHERE foo = '123';
This is laziness on my part and could be fixed without too much effort.
For common constraints, the row is checked to see if it satisfies the query's constraints before returning control to SQLite's virtual machine. This minimizes the number of allocations performed when many rows are filtered out by the user's criteria.
Individual clauses are mapped to the row groups they match.
eg going on row group statistics, which store minimum and maximum values, a clause
WHERE city = 'Dawson Creek' may match 80% of row groups.
In reality, it may only be present in one or two row groups.
This is recorded in a shadow table so future queries that contain that clause can read only the necessary row groups.
These Parquet types are supported:
- INT96 timestamps (exposed as milliseconds since the epoch)
- UTF8 strings
- Variable- and fixed-length byte arrays
These are not currently supported: