Python fetchall slow fetchall() method in Python's SQL queries. fetchmany(100) # 关闭数据库连接 . rows = c. – Oct 27, 2012 · At the moment I'm using python to do this, but the fetch command takes 1-2 hours to complete about 2000 Events, which is far too slow, since I need to process about 1000000 events. It just seems to convert result to list. fetchall() fetches all the rows of a query result. I've created a connection with python through the odbc library, but a simple select statement (single column table, 4 rows) takes around 4 seconds to run. It seems that it takes too long when fetching large amount of dataset, I used pandas read_sql to get the result, but the performance is same when using session. This problem can arise when dealing with large datasets, and we will discuss possible solutions and best practices to optimize the performance of your SQL queries. 为避免 fetchall 方法卡住，我们可以考虑使用 fetchmany 或者 fetchone 方法来逐批获取数据，这样可以降低内存的使用量。 下面是一个示例代码，演示了如何使用 fetchmany 方法来避免 fetchall 方法卡住的情况： # 连接数据库 . Here is the result comparision for sample size = 10000, 50000, 100000, 500000. SQLite 在 Python 上的 fetchone 操作较慢，fetchall 操作会卡住 在本文中，我们将介绍在使用 SQLite 数据库时，Python 中的 fetchone 操作为什么较慢，以及为何 fetchall 操作会卡住的原因。我们还将提供示例说明来帮助读者更好地理解这个问题。 Jan 26, 2016 · I compare the operating time when fetching large amount of dataset among teradata python module, ODBC(with pyodbc), and JDBC(with jaydebeapi). . fetchall() directly. I am going to use another database (MongoDB) which seems to be much faster for what I am doing. – Mar 4, 2011 · I think it indeed depends on the implementation, but you can get an idea of the differences by looking into MySQLdb sources. Running it in the query window of sql server is instant, but for some reason it is extremely slow when using python and the odbc library. It returns all the rows as a list of tuples. Sep 5, 2020 · I've created a connection with python through the odbc library, but a simple select statement (single column table, 4 rows) takes around 4 seconds to run. append([eventNumber, degree]) Jun 3, 2019 · python使用pymysql操作数据库，速度太慢，已解决-----mysql-connector-python 小编使用python的pymysql操作数据库使发现，网页的加载速度特别慢，正常加载时间应该是零点几秒，可是用pymysql加载的速度高至十几秒，开始分析时，认为是图片，js，css …内存过大，然后用了 Sep 4, 2019 · This a batch process, not an app. fetchone is slow because it has to execute all subqueries for each record in r_ele. 在本文中，我们介绍了为什么在使用 SQLite 数据库时，Python 中的 fetchone 操作较慢，以及为何 fetchall 操作会卡住的原因。 我们了解到 fetchone 方法是逐行逐行地读取数据，导致每次读取数据都会有一定的延迟，特别对于大型数据库。 而 fetchall 方法一次性获取全部结果，可能导致内存消耗过大，从而程序卡住。 Jan 26, 2016 · It seems that it takes too long when fetching large amount of dataset, I used pandas read_sql to get the result, but the performance is same when using session. Depending on the options, mysqldb fetch* keep the current set of rows in memory or server side, so fetchmany vs fetchone has some flexibility here to know what to keep in (python's) memory and what to keep db server side. Jan 25, 2018 · We are experiencing a linear time complexity when returning larger query-sets (anything over 10k rows). I've changed some things around and got some speed-up, but it still takes over an hour for the select statement to finish. Nov 16, 2012 · I asked two related questions ( How can I speed up fetching the results after running an sqlite query? and Is it normal that sqlite. By default fetchall() is as slow as looping over fetchone() due to the arraysize of the Cursor object being set to 1. I reduced the amount of data stored in my table building better relationship, and have been more accurate in my queries which helps. An empty list is returned if there is no record to fetch. To eliminate all possible factors stemming from table structure and/or query complexity, I ended up creating a row generator which unfortunately suffers the same fate, but demonstrates the problem nicely. I assumed execute was lazy as there are fetchall and fetchmeny methods available. cursor. If full result is already available, I don't see any point in calling fetchall. This is my fetching part, which takes so long: _degrees = [] for degree, eventNumber in cursor. WITH data(r) AS ( SELECT 1 r FROM dual. fetchall(): _degrees. To speed things up you can loop over fetchmany() , but to see a performance gain, you need to provide it with a size parameter bigger than 1, otherwise it'll fetch "many" by batches of arraysize , i. I need to process this data a bit and move to different place. fetchall is even slower because it takes just as long as if you had executed fetchone for all records. Mar 9, 2021 · cursor. Nov 16, 2012 · I asked two related questions ( How can I speed up fetching the results after running an sqlite query? and Is it normal that sqlite. fetchmany(size) returns the number of rows specified by size argument. fetchall() is so slow?). Aug 21, 2013 · SQLite computes result records on the fly. Nov 20, 2015 · @Justin, not really. 1. e. Sep 12, 2024 · In this article, we will explore the issue of slow fetching speed when using the cursor. I tend to think that the pyodbc connector is just slow using Python. ewuxam ollhzx bbvxa isqfe alkzz paw eijyxi waem ygvlkvs xmpwbl ugsp izwh aiuafn jclc cdxtx