This series of posts discuss processing of common crawl dataset on laptop.
Introduction
Common Crawl(CC)1 is an open repository of web containing peta bytes of data since 2008. As the dataset is huge, most of the tutorials use AWS EMR/Athena to process the data.
In this post, let's learn how to extract a subset of data(entire telugu language web pages) and process it on our local machine.
Exploring Common Crawl
CC provides monthly data dumps in WARC format. Each crawl consists of about ~3 billion web pages with a compressed size of ~100 TB.
In addition to WARC files, CC provides index files as well as columnar index2 files so that users can easily search, filter and download the data.
Common Crawl Index
Each crawl index is spread over 300 files consisting of ~250 GB of data. For this post, let use the latest crawl which is CC-MAIN-2022-40.
The index files can be accessed from AWS S3 or https. We can use aws cli to list all the files along with the sizes.
$ aws s3 ls --recursive --human-readable --summarize s3://commoncrawl/cc-index/collections/CC-MAIN-2022-40
2022-10-08 16:07:59 621.9 MiB cc-index/collections/CC-MAIN-2022-40/indexes/cdx-00000.gz
2022-10-08 16:08:26 721.6 MiB cc-index/collections/CC-MAIN-2022-40/indexes/cdx-00001.gz
...
2022-10-08 16:42:39 146.6 MiB cc-index/collections/CC-MAIN-2022-40/indexes/cluster.idx
2022-10-08 16:42:33 30 Bytes cc-index/collections/CC-MAIN-2022-40/metadata.yaml
Total Objects: 302
Total Size: 236.1 GiB
Let's download an index file to our local machine and see how the data is arranged. We can use aws cli to download the data from s3 bucket or use wget to download it from https endpoint.
# from s3
$ aws s3 cp s3://commoncrawl/cc-index/collections/CC-MAIN-2022-40/indexes/cdx-00000.gz .
# from https
$ wget https://data.commoncrawl.org/cc-index/collections/CC-MAIN-2022-40/indexes/cdx-00000.gz
Let's print top five lines of the file.
$ zcat < cdx-00000.gz | head -n 5
0,1,184,137)/1klikbet 20221005193707 {"url": "http://137.184.1.0/1klikbet/", "mime": "text/html", "mime-detected": "text/html", "status": "200", "digest": "XTKGORHKLZCHDBBOMYCYYIZVRPMXNRII", "length": "7065", "offset": "83437", "filename": "crawl-data/CC-MAIN-2022-40/segments/1664030337663.75/warc/CC-MAIN-20221005172112-20221005202112-00011.warc.gz", "charset": "UTF-8", "languages": "ind"}
0,1,184,137)/7meter 20221005192131 {"url": "http://137.184.1.0/7meter/", "mime": "text/html", "mime-detected": "text/html", "status": "200", "digest": "KUJAMRT6MXYR3RTWRJTIWJ5T2ZUB3EBH", "length": "7456", "offset": "142680", "filename": "crawl-data/CC-MAIN-2022-40/segments/1664030337663.75/warc/CC-MAIN-20221005172112-20221005202112-00182.warc.gz", "charset": "UTF-8", "languages": "ind"}
...
The last column of each line contains the language information. We can use these index files, and we can extract all the lines containing tel language code.
Columnar Index
We can also use columnar index to filter out telugu language web pages. Let's download a single file from the index.
# from s3
$ aws s3 cp s3://commoncrawl/cc-index/table/cc-main/warc/crawl=CC-MAIN-2022-40/subset=warc/part-00001-26160df0-1827-4787-a515-95ecaa2c9688.c000.gz.parquet .
# from https
$ wget https://data.commoncrawl.org/cc-index/table/cc-main/warc/crawl=CC-MAIN-2022-40/subset=warc/part-00001-26160df0-1827-4787-a515-95ecaa2c9688.c000.gz.parquet
We can use Python pandas to read the parquet file and filter out telugu language web pages. Columnar index has content_languages column which can be use to filter out telugu pages.
$ python -c """
import pandas as pd
filename = 'part-00000-26160df0-1827-4787-a515-95ecaa2c9688.c000.gz.parquet'
df = pd.read\_parquet(filename)
df = df[df['content\_languages'].str.startswith('tel', na=False)]
df.to\_csv('telugu.csv')
"""
Improving Performance
Faster Downloads
I have used Macbook M1 with local ISP to download and extract the index. It took around 7 minutes to download a single file and 2 minutes to extract the data. To process 300 index files, it takes ~2 days.
Let's see how we can speed it up.
My Wi-Fi speed is ~4MBps when downloading the index file. To download faster, I have created t2.micro(free-tier) EC2 instance on AWS. In this machine, download speed is ~10MBps. We can use other instances, but I am trying to use only free resources. In this machine, single file download is taking ~3 minutes.
CC dataset is hosted in us-east-1 region. So, I have created a new t2.micro instance in us-east-1 region. This instance is taking <20 seconds to download a single file. We can download entire index in less than 2 hours.
Faster Performance
To extract data from index files, we have used Python pandas without specifying the engine. By default it uses pyarrow which is bit slow. To imrpove speed we can use fastparquet as engine which is ~5x faster than pyarrow.
filename = 'part-00000-26160df0-1827-4787-a515-95ecaa2c9688.c000.gz.parquet'
df = pd.read\_parquet(filename, engine='fastparquet')
To get better performance, we can use duckdb. Duckdb can read parquet files. We can write a simple SQL query to filter out the required rows.
$ duckdb -c """
LOAD parquet;
COPY (select \* from PARQUET\_SCAN('part-00000-26160df0-1827-4787-a515-95ecaa2c9688.c000.gz.parquet') where content\_languages ilike '%tel%') TO 'te0001.csv' (DELIMITER ',', HEADER TRUE);
"""
With duckdb, we can even give the remote url directly to the query.
duckdb -c """
LOAD httpfs;
LOAD parquet;
COPY (select \* from PARQUET\_SCAN('s3://commoncrawl/cc-index/table/cc-main/warc/crawl=CC-MAIN-2022-40/subset=warc/part-00001-26160df0-1827-4787-a515-95ecaa2c9688.c000.gz.parquet') where content\_languages ilike '%tel%') TO 'te0001.csv' (DELIMITER ',', HEADER TRUE);"""
"""
Depending on the file size, duckdb takes 10-15 seconds to process a single file. With this, entire index can be processed in an hour.
Conclusion
We can write a simple shell script as shown below to extract data from the index files.
#! /bin/zsh
set -x
duckdb -c 'INSTALL parquet;'
duckdb -c 'INSTALL httpfs;'
for i in {0000..0300};
do
duckdb -c """
LOAD httpfs;
LOAD parquet;
SET s3\_region='us-east-1';
SET s3\_access\_key\_id='s3\_secret\_access\_key';
SET s3\_secret\_access\_key='s3\_secret\_access\_key';
COPY (select \* from PARQUET\_SCAN('s3://commoncrawl/cc-index/table/cc-main/warc/crawl=CC-MAIN-2022-40/subset=warc/part-0$i-26160df0-1827-4787-a515-95ecaa2c9688.c000.gz.parquet') where content\_languages ilike '%tel%') TO 'te$i.csv' (DELIMITER ',', HEADER TRUE);"""
done
With this script, we can extract a subset of index from CC in < 3 hours.
In the upcoming posts, let's see how we can fetch the data from WARC files using this index and do further data processing.
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