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Show HN: SQL on CSV/TSV/etc + native/WASM + worlds fastest CSV parser

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Please note: this code is still alpha / pre-production. Everything here should be considered preliminary.

If you like zsv+lib, please give it a star!

zsv+lib: the world’s fastest CSV parser, with an extensible CLI

zsv+lib is a fast CSV parser library and extensible command-line utility.
It achieves high performance using SIMD operations,
efficient memory use and other optimization techniques.


Preliminary performance results compare favorably vs other CSV utilities (xsv, tsv-utils, csvkit, mlr (miller) etc).
Below were results on a pre-M1 OSX MBA; on most platforms zsvlib was 2x faster, though in some cases the advantage was as small as
20% (see also M1 update note below):

count speedselect speed

** See 12/19 update re M1 processor at

Built-in and extensible features

zsv is an extensible CSV utility, which uses zsvlib,
for tasks such as slicing and dicing, querying with SQL,
combining, converting, serializing, flattening and more.

zsv is streamlined for easy development of custom dynamic extensions, one of which is
available here and offers added features such as statification and validation reporting,
automated column mapping and transformation, and github-like capabilities for sharing
and collaboration.

zsvlib and zsv are written in C, but since zsvlib is a library, and zsv
extensions are just shared libraries, you can extend zsv with
your own code in any programming language, so long as it has been compiled
into a shared library that implements the expected interface.

Key highlights

  • Available as BOTH a library and an application
  • Open-source, permissively licensed
  • Handles real-world CSV the same way that spreadsheet programs do (including
    edge cases
    ). Gracefully handles (and can “clean”) real-world data that may be
  • Runs on OSX (tested on clang/gcc), Linux (gcc), Windows (mingw),
    BSD (gcc-only) and in-browser (emscripten/wasm)
  • Fast (maybe the fastest ever?). See
  • Low memory usage (regardless of how big your data is)
  • Easy to use as a library in a few lines of code
  • Includes ZSV command-line app with batteries:
    • select, count, sql query, describe, flatten, serialize and more
  • Easy to extend/customize zsv with a few lines of code via modular plug-in framework.
    Just write a few custom functions and compile into a distributable DLL that any existing zsv
    installation can use
  • zsvlib and zsv are permissive licensed
  • Coming soon!: free extension with added capabilities:
    • generate multi-tab XLSX validation break-out reports
    • generate multi-table XLSX or CSV stratifications
    • automate column mapping and transformations
    • create, train and share re-usable data domains using github-like features

Binary downloads

Pre-built binaries for OSX, Windows, Linux and BSD are available at


zsv runs best (and by far, fastest) as a desktop CLI. But, you can also try out an extended
version in the browser (though it runs much slower), at A tutorial that demonstrates a small subset of the
capabilities of ZSV and the ZSVHub extension is available at

Why another CSV parser / utility?

Our objectives, which we were unable to find in a pre-existing project, are:

  • Reasonably high performance
  • Available as both a library and a standalone executable / command-line interface utility (CLI)
  • Memory-efficient, configurable resource limits
  • Handles real-world CSV cases the same way that Excel does, including all edge cases
    (quote handling, newline handling (either n or r), embedded newlines,
    abnormal quoting (e.g. aaa”aaa,bbb…)
  • Handles other “dirty” data issues:
    • Assumes valid UTF8, but does not misbehave if input contains bad UTF8
    • Option to specify multi-row headers
    • Does not assume or stop working in the case of inconsistent numbers of columns
  • Easy to use library or extend/customize CLI

There are several excellent tools that achieve high performance. Among those we
considered were xsv and tsv-utils. While they met our performance
objective, both were designed primarily as a utility and not a library, and
were not easy enough, for our needs, to customize. This was because they were not designed
for modular customizations that could be maintained (or licensed) independently
of the related project (in addition to the fact that they were written in Rust
and D, respectively, which happen to be languages with which we lacked deep
experience). Others we considered were Miller (mlr), csvkit and Go (csv module), which did not meet our performance objective.
We also considered various libraries using SIMD, but none seemed to (yet) meet the “real-world CSV” objective.

Hence zsv was created as a library and a versatile application, both optimized for speed
and ease of development for extending and/or customizing to your needs

Batteries included

zsv comes with several built-in commands:

  • echo: read CSV from stdin and write it back out to stdout. This is mostly
    useful for demonstrating how to use the API and also how to create a plug-in,
    and has some limited utility beyond that e.g. for adding/removing the UTF8 BOM,
    or cleaning up bad UTF8
  • select: re-shape CSV by skipping leading garbage, combining header rows into
    a single header, selecting or excluding specified columns, removing duplicate
    columns, sampling, searching and more
  • sql: run ad-hoc SQL query on a CSV file
  • desc: provide a quick description of your table data
  • pretty: format for console (fixed-width) display, or convert to markdown
  • 2json, 2tsv: convert CSV to JSON or TSV
  • serialize (inverse of flatten): convert an NxM table to a single 3x (Nx(M-1))
    table with columns: Row, Column Name, Column Value
  • flatten (inverse of serialize): flatten a table by combining rows that share
    a common value in a specified identifier column
  • stack: merge CSV files vertically

Each of these can also be built as an independent executable.

Building and installing the CLI

Basically: ./configure && sudo make install

See for more details.

Running the CLI

After installing, run zsv help to see usage details. The typical syntax is zsv


zsv sql my_population_data.csv "select * from data where population > 100000"

Third-party extensions

In addition to the above extensions, at least one third-party extensions will be made
available. If you would like to add your extensions to this list, please contact the
project maintainers.

Creating your own extension

You can extend zsv by providing a pre-compiled shared or static library that
defines the functions specified in extension_template.h and which zsv loads in
one of three ways:

  • as a static library that is statically linked at compile time
  • as a dynamic library that is linked at compile time and located in any
    library search path
  • as a dynamic library that is located in the same folder as the zsv executable
    and loaded at runtime if/as/when the custom mode is invoked

Example and template

You can build and run a sample extension by running make test from app/ext_example.

The easiest way to implement your own extension is to
copy and customize the template files in app/ext_template

Alpha release limitations

This alpha release does not yet implement the full range of core features
that are planned for implementation prior to beta release. If you are interested in
helping, please post an issue.

Possible enhancements and related developments

  • online “playground” See
  • optimize search; add search with hyperscan or re2 regex matching, possibly parallelize?
  • auto-generated documentation, and better documentation in general
  • Additional benchmarking. Would be great to use as a springboard to benchmarking a number of various tasks
  • encoding conversion e.g. UTF16 to UTF8

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