mirror of
https://github.com/cldellow/sqlite-parquet-vtable.git
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177 lines
5.2 KiB
Markdown
177 lines
5.2 KiB
Markdown
# sqlite-parquet-vtable
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[](https://travis-ci.org/cldellow/sqlite-parquet-vtable)
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[](https://codecov.io/gh/cldellow/sqlite-parquet-vtable)
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A SQLite [virtual table](https://sqlite.org/vtab.html) extension to expose Parquet files as SQL tables. You may also find [csv2parquet](https://github.com/cldellow/csv2parquet/) useful.
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This [blog post](https://cldellow.com/2018/06/22/sqlite-parquet-vtable.html) provides some context on why you might use this.
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## For Linux
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### Installing
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#### Download
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You can fetch a version built for Ubuntu 16.04 at https://s3.amazonaws.com/cldellow/public/libparquet/libparquet.so.xz
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#### Building
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```
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./make-linux
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```
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The first run will git clone a bunch of libraries, patch them to be statically linkable and build them.
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Subsequent builds will only build the parquet virtual table extension.
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#### Building (release)
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Run `./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.
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#### Tests
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Run:
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```
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tests/create-queries-from-templates
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tests/test-all
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```
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## Use
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```
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$ sqlite/sqlite3
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sqlite> .load build/linux/libparquet
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sqlite> CREATE VIRTUAL TABLE demo USING parquet('parquet-generator/99-rows-1.parquet');
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sqlite> SELECT * FROM demo;
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...if all goes well, you'll see data here!...
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```
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Note: if you get an error like:
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```
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sqlite> .load build/linux/libparquet
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Error: parquet/libparquet.so: wrong ELF class: ELFCLASS64
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```
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You have the 32-bit SQLite installed. To fix this, do:
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```
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sudo apt-get remove --purge sqlite3
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sudo apt-get install sqlite3:amd64
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```
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## For Windows
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The following steps were performed on Windows 10 x64 system.
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### Build
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#### 1 Apache-arrow build
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Configure the environment and build Apache-arrow as follows:
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https://github.com/apache/arrow/blob/apache-arrow-0.9.0/cpp/apidoc/Windows.md
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Once the build is complete, files such as arrow.lib, arrow.dll, and so on are generated.
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#### 2 Parquet-cpp build
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Configure the environment and build Parquet-cpp as follows:
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https://github.com/apache/parquet-cpp/blob/apache-parquet-cpp-1.4.0/docs/Windows.md
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The version of boost-cpp can be specified as 1.66.0 to avoid version compatibility issues. Once the build is complete, files such as parquet.lib, parquet.dll, and so on are generated.
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#### 3 Sqlite3 build
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1 Download and extract the following three packages into the same folder.
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sqlite-amalgamation-3490100.zip
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sqlite-dll-win-x64-3490100.zip
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sqlite-autoconf-3490100.tar.gz
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2 Open the developer command prompt for VS 2017, switch to the above folder, and run the following command:
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`lib /DEF:sqlite3.def /OUT:sqlite3.lib `
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After the command is executed, sqlite3.lib was generated.
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#### 4 sqlite-parquet-vtable (windows) build
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1 Open the parquet directory of sqlite-parquet-vtable as dll in VS2017.
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2 Configure the paths for dll, lib, and header files in VS2017.
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3 Modify all the “constexpr” in type.h in the source code of arrow to “const”.
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4 Build this project, if successful, will generate sqlite-parquet-vtable.lib and sqlite-parquet-vtable.dll.
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### Use
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1 Create a new directory{your-directory}
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2 Copy the generated arrow.dll, parquet.dll, sqlite-parquet-vtable.dll from steps 1-4 to {your directory}, and also copy all dlls from C:\local\boost_1_66_0\lib64-msvc-14.1（Your actual boost installation path.） to {your directory}.
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```
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$ sqlite\sqlite3.exe
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sqlite> .load sqlite-parquet-vtable.dll
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sqlite> CREATE VIRTUAL TABLE demo USING parquet('parquet-generator/99-rows-1.parquet');
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sqlite> SELECT * FROM demo;
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...if all goes well, you'll see data here!...
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```
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## Supported features
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### Row group filtering
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Row group filtering is supported for strings and numerics so long as the SQLite
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type matches the Parquet type.
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e.g. if you have a column `foo` that is an INT32, this query will skip row groups whose
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statistics prove that it does not contain relevant rows:
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```
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SELECT * FROM tbl WHERE foo = 123;
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```
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but this query will devolve to a table scan:
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```
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SELECT * FROM tbl WHERE foo = '123';
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```
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This is laziness on my part and could be fixed without too much effort.
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### Row filtering
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For common constraints, the row is checked to see if it satisfies the query's
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constraints before returning control to SQLite's virtual machine. This minimizes
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the number of allocations performed when many rows are filtered out by
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the user's criteria.
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### Memoized slices
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Individual clauses are mapped to the row groups they match.
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eg going on row group statistics, which store minimum and maximum values, a clause
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like `WHERE city = 'Dawson Creek'` may match 80% of row groups.
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In reality, it may only be present in one or two row groups.
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This is recorded in a shadow table so future queries that contain that clause
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can read only the necessary row groups.
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### Types
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These Parquet types are supported:
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* INT96 timestamps (exposed as milliseconds since the epoch)
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* INT8/INT16/INT32/INT64
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* UTF8 strings
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* BOOLEAN
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* FLOAT
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* DOUBLE
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* Variable- and fixed-length byte arrays
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These are not currently supported:
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* UINT8/UINT16/UINT32/UINT64
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* DECIMAL
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