Loading Data from The Local Filesystem
to CockroachDB
in Python with dlt
We will be using the dlt PostgreSQL destination to connect to CockroachDB. You can get the connection string for your CockroachDB database as described in the CockroachDB Docs.
Join our Slack community or book a call with our support engineer Violetta.
This documentation covers the process of loading data from The Local Filesystem
to CockroachDB
using the open-source Python library dlt
. The Local Filesystem
source allows for seamless streaming of CSV, Parquet, and JSONL files with the reader
source. CockroachDB
offers a simple and reliable SQL API, is distributed, cloud-native, Kubernetes compatible, and free up to 5GB and 1vCPU. The integration leverages dlt
to efficiently manage the data transfer. For further details on The Local Filesystem
source, visit this link.
dlt
Key Features
- Write Disposition Handling: Learn how
dlt
handles different write dispositions such asappend
,replace
, andmerge
. Read more - DuckDB Integration: Discover how to set up and use DuckDB as a destination for your
dlt
pipelines. Read more - Memory and Disk Management: Understand how to control in-memory buffers and intermediary file sizes to optimize performance. Read more
- Governance Support: Explore the governance features in
dlt
pipelines, including metadata utilization, schema enforcement, and schema change alerts. Read more - Data Types: Get detailed information on the different data types supported by
dlt
and their precision and scale. Read more
Getting started with your pipeline locally
0. Prerequisites
dlt
requires Python 3.8 or higher. Additionally, you need to have the pip
package manager installed, and we recommend using a virtual environment to manage your dependencies. You can learn more about preparing your computer for dlt in our installation reference.
1. Install dlt
First you need to install the dlt
library with the correct extras for CockroachDB
:
pip install "dlt[postgres]"
The dlt
cli has a useful command to get you started with any combination of source and destination. For this example, we want to load data from The Local Filesystem
to CockroachDB
. You can run the following commands to create a starting point for loading data from The Local Filesystem
to CockroachDB
:
# create a new directory
mkdir filesystem_local_pipeline
cd filesystem_local_pipeline
# initialize a new pipeline with your source and destination
dlt init filesystem postgres
# install the required dependencies
pip install -r requirements.txt
The last command will install the required dependencies for your pipeline. The dependencies are listed in the requirements.txt
:
dlt[postgres]>=0.4.3a0
openpyxl>=3.0.0
You now have the following folder structure in your project:
filesystem_local_pipeline/
├── .dlt/
│ ├── config.toml # configs for your pipeline
│ └── secrets.toml # secrets for your pipeline
├── filesystem/ # folder with source specific files
│ └── ...
├── filesystem_pipeline.py # your main pipeline script
├── requirements.txt # dependencies for your pipeline
└── .gitignore # ignore files for git (not required)
2. Configuring your source and destination credentials
The dlt
cli will have created a .dlt
directory in your project folder. This directory contains a config.toml
file and a secrets.toml
file that you can use to configure your pipeline. The automatically created version of these files look like this:
generated config.toml
# put your configuration values here
[runtime]
log_level="WARNING" # the system log level of dlt
# use the dlthub_telemetry setting to enable/disable anonymous usage data reporting, see https://dlthub.com/docs/telemetry
dlthub_telemetry = true
[sources.filesystem]
bucket_url = "bucket_url" # please set me up!
generated secrets.toml
# put your secret values and credentials here. do not share this file and do not push it to github
[sources.filesystem.credentials]
aws_access_key_id = "aws_access_key_id" # please set me up!
aws_secret_access_key = "aws_secret_access_key" # please set me up!
[destination.postgres]
dataset_name = "dataset_name" # please set me up!
[destination.postgres.credentials]
database = "database" # please set me up!
password = "password" # please set me up!
username = "username" # please set me up!
host = "host" # please set me up!
port = 5432
connect_timeout = 15
2.1. Adjust the generated code to your usecase
The default filesystem source is configured to load from AWS S3. To load from the local filesystem, remove the [sources.filesystem.credentials]
section from your secrets.toml.
You can also set up your bucket_url
(which is the local file path) and file_glob
in the config.toml
[sources.filesystem] # use [sources.readers.credentials] for the "readers" source
bucket_url="file://path/to/my/output"
file_glob="*"
3. Running your pipeline for the first time
The dlt
cli has also created a main pipeline script for you at filesystem_pipeline.py
, as well as a folder filesystem
that contains additional python files for your source. These files are your local copies which you can modify to fit your needs. In some cases you may find that you only need to do small changes to your pipelines or add some configurations, in other cases these files can serve as a working starting point for your code, but will need to be adjusted to do what you need them to do.
The main pipeline script will look something like this:
import os
import posixpath
from typing import Iterator
import dlt
from dlt.sources import TDataItems
try:
from .filesystem import FileItemDict, filesystem, readers, read_csv # type: ignore
except ImportError:
from filesystem import (
FileItemDict,
filesystem,
readers,
read_csv,
)
TESTS_BUCKET_URL = posixpath.abspath("../tests/filesystem/samples/")
def stream_and_merge_csv() -> None:
"""Demonstrates how to scan folder with csv files, load them in chunk and merge on date column with the previous load"""
pipeline = dlt.pipeline(
pipeline_name="standard_filesystem_csv",
destination='postgres',
dataset_name="met_data",
)
# met_data contains 3 columns, where "date" column contain a date on which we want to merge
# load all csvs in A801
met_files = readers(
bucket_url=TESTS_BUCKET_URL, file_glob="met_csv/A801/*.csv"
).read_csv()
# tell dlt to merge on date
met_files.apply_hints(write_disposition="merge", merge_key="date")
# NOTE: we load to met_csv table
load_info = pipeline.run(met_files.with_name("met_csv"))
print(load_info)
print(pipeline.last_trace.last_normalize_info)
# now let's simulate loading on next day. not only current data appears but also updated record for the previous day are present
# all the records for previous day will be replaced with new records
met_files = readers(
bucket_url=TESTS_BUCKET_URL, file_glob="met_csv/A801/*.csv"
).read_csv()
met_files.apply_hints(write_disposition="merge", merge_key="date")
load_info = pipeline.run(met_files.with_name("met_csv"))
# you can also do dlt pipeline standard_filesystem_csv show to confirm that all A801 were replaced with A803 records for overlapping day
print(load_info)
print(pipeline.last_trace.last_normalize_info)
def read_csv_with_duckdb() -> None:
pipeline = dlt.pipeline(
pipeline_name="standard_filesystem",
destination='postgres',
dataset_name="met_data_duckdb",
)
# load all the CSV data, excluding headers
met_files = readers(
bucket_url=TESTS_BUCKET_URL, file_glob="met_csv/A801/*.csv"
).read_csv_duckdb(chunk_size=1000, header=True)
load_info = pipeline.run(met_files)
print(load_info)
print(pipeline.last_trace.last_normalize_info)
def read_csv_duckdb_compressed() -> None:
pipeline = dlt.pipeline(
pipeline_name="standard_filesystem",
destination='postgres',
dataset_name="taxi_data",
full_refresh=True,
)
met_files = readers(
bucket_url=TESTS_BUCKET_URL,
file_glob="gzip/*",
).read_csv_duckdb()
load_info = pipeline.run(met_files)
print(load_info)
print(pipeline.last_trace.last_normalize_info)
def read_parquet_and_jsonl_chunked() -> None:
pipeline = dlt.pipeline(
pipeline_name="standard_filesystem",
destination='postgres',
dataset_name="teams_data",
)
# When using the readers resource, you can specify a filter to select only the files you
# want to load including a glob pattern. If you use a recursive glob pattern, the filenames
# will include the path to the file inside the bucket_url.
# JSONL reading (in large chunks!)
jsonl_reader = readers(TESTS_BUCKET_URL, file_glob="**/*.jsonl").read_jsonl(
chunksize=10000
)
# PARQUET reading
parquet_reader = readers(TESTS_BUCKET_URL, file_glob="**/*.parquet").read_parquet()
# load both folders together to specified tables
load_info = pipeline.run(
[
jsonl_reader.with_name("jsonl_team_data"),
parquet_reader.with_name("parquet_team_data"),
]
)
print(load_info)
print(pipeline.last_trace.last_normalize_info)
def read_custom_file_type_excel() -> None:
"""Here we create an extract pipeline using filesystem resource and read_csv transformer"""
# instantiate filesystem directly to get list of files (FileItems) and then use read_excel transformer to get
# content of excel via pandas
@dlt.transformer(standalone=True)
def read_excel(
items: Iterator[FileItemDict], sheet_name: str
) -> Iterator[TDataItems]:
import pandas as pd
for file_obj in items:
with file_obj.open() as file:
yield pd.read_excel(file, sheet_name).to_dict(orient="records")
freshman_xls = filesystem(
bucket_url=TESTS_BUCKET_URL, file_glob="../custom/freshman_kgs.xlsx"
) | read_excel("freshman_table")
load_info = dlt.run(
freshman_xls.with_name("freshman"),
destination='postgres',
dataset_name="freshman_data",
)
print(load_info)
def copy_files_resource(local_folder: str) -> None:
"""Demonstrates how to copy files locally by adding a step to filesystem resource and the to load the download listing to db"""
pipeline = dlt.pipeline(
pipeline_name="standard_filesystem_copy",
destination='postgres',
dataset_name="standard_filesystem_data",
)
# a step that copies files into test storage
def _copy(item: FileItemDict) -> FileItemDict:
# instantiate fsspec and copy file
dest_file = os.path.join(local_folder, item["relative_path"])
# create dest folder
os.makedirs(os.path.dirname(dest_file), exist_ok=True)
# download file
item.fsspec.download(item["file_url"], dest_file)
# return file item unchanged
return item
# use recursive glob pattern and add file copy step
downloader = filesystem(TESTS_BUCKET_URL, file_glob="**").add_map(_copy)
# NOTE: you do not need to load any data to execute extract, below we obtain
# a list of files in a bucket and also copy them locally
# listing = list(downloader)
# print(listing)
# download to table "listing"
# downloader = filesystem(TESTS_BUCKET_URL, file_glob="**").add_map(_copy)
load_info = pipeline.run(
downloader.with_name("listing"), write_disposition="replace"
)
# pretty print the information on data that was loaded
print(load_info)
print(pipeline.last_trace.last_normalize_info)
def read_files_incrementally_mtime() -> None:
pipeline = dlt.pipeline(
pipeline_name="standard_filesystem_incremental",
destination='postgres',
dataset_name="file_tracker",
)
# here we modify filesystem resource so it will track only new csv files
# such resource may be then combined with transformer doing further processing
new_files = filesystem(bucket_url=TESTS_BUCKET_URL, file_glob="csv/*")
# add incremental on modification time
new_files.apply_hints(incremental=dlt.sources.incremental("modification_date"))
load_info = pipeline.run((new_files | read_csv()).with_name("csv_files"))
print(load_info)
print(pipeline.last_trace.last_normalize_info)
# load again - no new files!
new_files = filesystem(bucket_url=TESTS_BUCKET_URL, file_glob="csv/*")
# add incremental on modification time
new_files.apply_hints(incremental=dlt.sources.incremental("modification_date"))
load_info = pipeline.run((new_files | read_csv()).with_name("csv_files"))
print(load_info)
print(pipeline.last_trace.last_normalize_info)
if __name__ == "__main__":
copy_files_resource("_storage")
stream_and_merge_csv()
read_parquet_and_jsonl_chunked()
read_custom_file_type_excel()
read_files_incrementally_mtime()
read_csv_with_duckdb()
read_csv_duckdb_compressed()
Provided you have set up your credentials, you can run your pipeline like a regular python script with the following command:
python filesystem_pipeline.py
4. Inspecting your load result
You can now inspect the state of your pipeline with the dlt
cli:
dlt pipeline filesystem_pipeline info
You can also use streamlit to inspect the contents of your CockroachDB
destination for this:
# install streamlit
pip install streamlit
# run the streamlit app for your pipeline with the dlt cli:
dlt pipeline filesystem_pipeline show
5. Next steps to get your pipeline running in production
One of the beauties of dlt
is, that we are just a plain Python library, so you can run your pipeline in any environment that supports Python >= 3.8. We have a couple of helpers and guides in our docs to get you there:
The Deploy section will show you how to deploy your pipeline to
- Deploy with GitHub Actions: Learn how to deploy your
dlt
pipeline using GitHub Actions for continuous integration and deployment. Follow the guide here. - Deploy with Airflow and Google Composer: Use Airflow and Google Composer to manage and schedule your
dlt
pipelines. Detailed instructions can be found here. - Deploy with Google Cloud Functions: Explore how to deploy your
dlt
pipeline using Google Cloud Functions for a serverless approach. Check the guide here. - More Deployment Options: Discover various other methods to deploy your
dlt
pipelines, including different cloud services and orchestration tools. Learn more here.
The running in production section will teach you about:
- How to Monitor your pipeline: Learn how to effectively monitor your
dlt
pipeline in production, ensuring smooth and reliable operation. How to Monitor your pipeline - Set up alerts: Configure alerts to get notified about important events and issues in your
dlt
pipeline, allowing for proactive management. Set up alerts - And set up tracing: Implement tracing to gain insights into the execution and performance of your
dlt
pipeline, helping you identify and resolve issues quickly. And set up tracing
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