Fetching DF shows up as memory corruption

[mauropagano]

1. What versions are you using?
   3.1.0 on python 3.9.6 and 3.12.7

2. Is it an error or a hang or a crash?
   Looks like memory corruption, running the code over and over at some point you see the same Arrow object printing junk (I don't think it goes back to db to re-run)
   This fails CONSISTENTLY if the same connection is used twice (I'm not sure that's expected or not), but it also fails (if you try enough) with a new connection

3. What error(s) or behavior you are seeing?
   Incorrect result, need to run a few times

4. Does your application call init_oracle_client()?
   Reproduces in both thin and thick, thick seems easier to trigger

5. Include a runnable Python script that shows the problem.

import oracledb
import pyarrow

                                                                                                                                                                                                                                                      
def f() -> pyarrow.Table:
    c = oracledb.connect("...")
    oracle_df = c.fetch_df_all(
        statement="select dbms_random.value from dual", arraysize=5000
    ) 
    pyarrow_table = pyarrow.Table.from_arrays(
        arrays=oracle_df.column_arrays(), names=oracle_df.column_names()
    ) 
    return pyarrow_table


df = f()
print(f"df: {df}")


df2 = f() # <-- no use of df2
print(f"df: {df}") 
print(f"df: {df}")

[cjbj]

@mauropagano thanks for your continued focus on dataframes.
What OS are you reproducing this on? What is your DB version?

[mauropagano]

Client is linux, db is 19.x.
It reproduces with select 1 from dual too btw, I just picked something else for the testcase

[mauropagano]

Just realized I never provided an output example. Below is one from thick mode, thin reproduces too but need to try a few times (5-10 probably)

Working case (commenting out df2 = f())

df: pyarrow.Table
N1: double
----
N1: [[0]]
df: pyarrow.Table
N1: double
----
N1: [[0]]
df: pyarrow.Table
N1: double
----
N1: [[0]]

Example of incorrect output (df2 = f() in code)

df: pyarrow.Table
N1: double
----
N1: [[0]]
df: pyarrow.Table
N1: double
----
N1: [[2.3682269498151e-310]]
df: pyarrow.Table
N1: double
----
N1: [[2.3682269498151e-310]]

[cjbj]

@mauropagano thanks for that. I had to change the connection handling before I could see it. Also using select 1 from dual makes it clearer.

def f(c) -> pyarrow.Table:
    oracle_df = c.fetch_df_all(
#        statement="select dbms_random.value from dual", arraysize=5000
        statement="select 1 from dual", arraysize=5000
    )
    pyarrow_table = pyarrow.Table.from_arrays(
        arrays=oracle_df.column_arrays(), names=oracle_df.column_names()
    )
    return pyarrow_table


c = oracledb.connect(user=un, password=pw, dsn=cs)

I'll let @anthony-tuininga and @aosingh dig into it.

[aosingh]

@mauropagano

I was able to reproduce this and it happens because of premature deallocation of the underlying OracleArrowArray. Let me check how to fix this and get back.