I’m trying to load a large DataFrame into a PostgreSQL table and I’m considering two different approaches. I would like to know which one is generally faster, or if there’s a better approach I should consider.
Method 1: Convert PySpark DataFrame to multiple CSV files and load them into PostgreSQL
filepath = "/base_path/psql_multiprocessing_data"
df.repartition(400).write.mode("overwrite").format("csv").save(filepath, header='false')
import glob
import psycopg2
from multiprocessing import Pool, cpu_count
file_path_list = sorted(glob.glob("/base_path/psql_multiprocessing_data/*.csv"))
def psql_copy_load(fileName):
con = psycopg2.connect(database="my_db", user="my_user", password="my_password", host="my_host", port="my_port")
cursor = con.cursor()
with open(fileName, 'r') as f:
cursor.copy_from(f, 'my_schema.my_table', sep=",")
con.commit()
con.close()
return fileName
with Pool(cpu_count()) as p:
p.map(psql_copy_load, file_path_list)
Method 2: Convert the PySpark DataFrame into smaller pandas DataFrame chunks, write to a StringIO buffer, and load directly into PostgreSQL
import math
from io import StringIO
chunks = math.ceil(df_ops.count / 100000)
chunk_result = None
chunk_count = 0
for i in range(0, chunks):
start_value = i * 100000
end_value = (i + 1) * 100000
df = df_ops.get_chunk(start_value, end_value) # custom function to get a chunk of 100,000 rows
sio = StringIO()
sio.write(df.toPandas().to_csv(index=None, header=None, sep=separator, na_rep='nan'))
sio.seek(0)
raw_connections = engine.raw_connection()
with raw_connections.cursor() as c:
c.copy_from(sio, table_name, columns=df.columns, sep=separator)
raw_connections.commit()
Context:
The DataFrame is very large, and I’m trying to optimize the load time into PostgreSQL.
Method 1 utilizes multiprocessing and CSV files, while Method 2 processes smaller chunks of data in memory and loads them directly.
Question:
Which of these methods is likely to be faster in practice?
Are there any significant trade-offs between these two methods that I should be aware of?
Is there a more efficient way to handle this type of data loading?
Any insights or recommendations would be greatly appreciated!
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