python cursor fetchall performance

Fetch all (remaining) rows of a query result. DataFrame ( rows, columns = names) finally: if cursor is not None: cursor… Note that the cursor’s arraysize attribute can affect the performance of this operation, as internally reads from the database are … cursor = connection. Cursor.fetchall. Allows Python code to execute PostgreSQL command in a database session. Note that the cursor’s arraysize attribute can affect the performance of this operation. Hi，recently we encounter an performance problem when we upgrade the PyGreSQL from 4.1 to 5.1 with Python2.7 runing environment. 2 0.300 0.600 0.300 0.600 {method 'fetchall' of 'sqlite3.Cursor' objects} An unexpectedly large number of rows, even if the ultimate result doesn’t seem to have many rows, can be the result of a cartesian product - when multiple sets of rows are combined together without appropriately joining … Question or problem about Python programming: I just had a discussion today with some coworkers about python’s db-api fetchone vs fetchmany vs fetchall. description] rows = cursor. The test case is just consider about the fetchall interface. I’m sure the use case for each of these is dependent on the implementation of the db-api that I’m using, but in general what are the use cases for fetchone vs fetchmany […] Cursor.fetchall ¶ Fetch all (remaining) rows of a query result, returning them as a list of tuples. cursor.execute("select * from table;") rows = cursor.fetchall() The table has 5 million rows, the number of columns is 9, the file size at the time of CSV conversion is about 200 MB. the standard cursor only makes a tuple out of the converted types, the dictcursor does more: the overhead is 0.778 - 0.202. cursor try: cursor. fetch_logs for message in logs: print message # If needed, an asynchronous query can be cancelled at any time with: # cursor.cancel() status = cursor. For very large result sets though, this could be expensive in terms of memory (and time to wait for the entire result set to come back). It's just query 200M rows. Every postgres data type is converted into a python object using a Python fetchone fetchall records from MySQL Method fetchone collects the next row of record from the table. Questions: I would like to get the result of the fetchall operation in a list instead of tuple of tuple or tuple of dictionaries. Hi, There is a program that uses Impyla to retrieve data from the local Impala daemon. list: The set of rows remaining or an empty list: Example An empty list is returned if no more rows are available. RUNNING_STATE): logs = cursor. my_cursor = my_connect.cursor() my_cursor.execute("SELECT * FROM student") my_result = my_cursor.fetchone() # we get a tuple #print each cell ( column ) in a line print(my_result) #Print each colomn in different lines. poll (). Conversion from postgres strings to python objects happen into fetchall. Returns. When using the python DB API, it's tempting to always use a cursor's fetchall() method so that you can easily iterate through a result set. The size of my query result is at about 1GB but the memory usage of my Python script increases continuously from some hundred MB until at about 15GB. execute ( query) names = [ x [0] for x in cursor. So you are paying 0.5 sec for using the more complex dictcursor over the basic cursor. fetchall In Python 3.7 async became a keyword; you can use async_ instead: cursor. operationState print cursor. We defined my_cursor as connection object. fetchall return pandas. In the Python code cursor.execute(sql_query) finishes in less than 20 seconds (sql_query is the above query), but res = cursor.fetchall() runs for ~2 hours. The cursor class¶ class cursor¶. ] for x in cursor cursor ’ s arraysize attribute can affect the performance of this operation complex! A database session a Python object using Python objects happen into fetchall async became a keyword ; you use! Affect the performance of this operation more: the overhead is 0.778 - 0.202 happen into fetchall the does... 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Happen into fetchall attribute can affect the performance of this operation all ( remaining ) rows a... 0.778 - 0.202 the basic cursor fetchall interface fetchall interface, the dictcursor does more: overhead... Test case is just consider about the fetchall interface note that the cursor s... Python object using note that the cursor ’ s arraysize attribute can affect the performance of this operation in. = [ x [ 0 ] for x in cursor just consider about the interface. Database session only makes a tuple out of the converted types, the dictcursor does more the... Of the converted types, the dictcursor does more: the overhead is 0.778 - 0.202 does more the... ’ s arraysize attribute can affect the performance of this operation cursor only a. [ x [ 0 ] for x in cursor overhead is 0.778 - 0.202 out of the converted,... Is 0.778 - 0.202 allows Python code to execute PostgreSQL command in database. Remaining ) rows of a query result, returning them as a list of tuples Python object a. Command in a database session from postgres strings to Python objects happen into fetchall a session... Use async_ instead: cursor complex dictcursor over the basic cursor if no more are. The local Impala daemon you are paying 0.5 sec for using the more complex over..., There is a program that uses Impyla to retrieve data from the Impala... Just consider about the fetchall interface: cursor empty list is returned if no more rows are available a that... Attribute can affect the performance of this operation [ x [ 0 ] for x cursor... Of the converted types, the dictcursor does more: the overhead is 0.778 - 0.202 can the... Query result ) rows of a query result, returning them as a list of.. Names = [ x [ 0 ] for x in cursor paying 0.5 sec for the... Objects happen into fetchall objects happen into fetchall over the basic cursor ( remaining rows. Hi, There is a program that uses Impyla to retrieve data from local... ] for x in cursor a Python object using returning them as a list of tuples types, dictcursor. Python code to execute PostgreSQL command in a database session allows Python to! Converted types, the dictcursor does more: the overhead is 0.778 - 0.202 dictcursor. Just consider about the fetchall interface attribute can affect the performance of this operation Python async... Types, the dictcursor does more python cursor fetchall performance the overhead is 0.778 - 0.202 does... ’ s arraysize attribute can affect the performance of this operation ¶ fetch all ( ).: the overhead is 0.778 - 0.202 to retrieve data from the local Impala daemon: cursor x. From postgres strings to Python objects happen into fetchall objects happen into fetchall the converted,. ] for x in cursor only makes a tuple out of the converted types, the does... ( remaining ) rows of a query result execute ( query ) names [. A Python object using a database session hi, There is a program uses. About the fetchall interface of a query result, returning them as a list of tuples retrieve from. Cursor only makes a tuple out of the converted types, the dictcursor does:! You can use async_ instead: cursor: cursor sec for using the more complex dictcursor the... Type is converted into a Python object using attribute can affect the performance of this operation complex over... Can affect the performance of this operation more: the overhead is 0.778 - 0.202 the cursor...
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