toshitanian opened a new issue #11469:
URL: https://github.com/apache/airflow/issues/11469
**Apache Airflow version**:
1.10
**Environment**:
- **Cloud provider or hardware configuration**:
On docker container (puckel/docker-airflow:1.10.9)
- **OS** (e.g. from /etc/os-release):
`Debian GNU/Linux 10 (buster)`
- **Kernel** (e.g. `uname -a`):
`Linux 3bf5943b9fbd 5.4.0-1025-gcp #25-Ubuntu SMP Fri Sep 11 15:02:15 UTC
2020 x86_64 GNU/Linux`
- **Install tools**:
Docker (puckel/docker-airflow:1.10.9)
**What happened**:
While using `MySqlToGoogleCloudStorageOperator`, some dumps of tables
uploaded to GCS had much less records than ones in source table. For example:
- source table: 890,206 records
- dump on GCS: 302,014 records
The definition of operator is:
```python
chunk_filesize = 256 * 1024 * 1024 # chunk size of files are 256MB
MySqlToGoogleCloudStorageOperator(
task_id=task_id,
mysql_conn_id=MYSQL_CONN,
google_cloud_storage_conn_id=GCS_CONN,
sql="SELECT * FROM some_table;",
bucket=BUCKET_NAME,
filename='file_name_in_bucket',
schema_filename="schema_filename_in_bucket"
approx_max_file_size_bytes=chunk_filesize,
dag=DAG,
)
```
**What you expected to happen**:
I expected that complete number of records are uploaded to GCS.
<!-- What do you think went wrong? -->
I suppose that the problem is caused when records are dumped into multiple
files while dumping records from tables. However, the operator overwrites the
files while uploading to GCS. The files are splitted by
`approx_max_file_size_bytes` (default: 1900000000bytes).
The temporary files are splitted by `approx_max_file_size_bytes` at the
lines below.
https://github.com/apache/airflow/blob/v1-10-stable/airflow/contrib/operators/sql_to_gcs.py#L183-L196
Then, the multiple temporary files are passed to `GcsHook.upload` in for
loop.
https://github.com/apache/airflow/blob/v1-10-stable/airflow/contrib/operators/sql_to_gcs.py#L265-L277
However, each temporary files are overwritten by give filename (object name)
in each iteration.
https://github.com/apache/airflow/blob/master/airflow/providers/google/cloud/hooks/gcs.py#L371-L374
This operator should be expected to upload and/or merge multiple temporary
files into one object file that includes complete records of source table.
These are temporary files while the operator is dumping records.
```
airflow airflow 11M Oct 12 13:13 tmp7uuj1skr
airflow airflow 256M Oct 12 13:13 tmpz3x8qtil
airflow@xxxx:/tmp$ cat tmpz3x8qtil | wc -l
674510
airflow@xxx:/tmp$ cat tmp7uuj1skr | wc -l
108770
```
The airflow log shows that the operator overwrites the object with each
temporary file in each interation.
```
[2020-10-12 13:14:49,990] {{gcs_hook.py:224}} INFO - File /tmp/tmpz3x8qtil
uploaded to masters/messages.json in <Bucket: dwh_work_ds> bucket
[2020-10-12 13:14:52,647] {{gcs_hook.py:224}} INFO - File /tmp/tmp7uuj1skr
uploaded to masters/messages.json in <Bucket: dwh_work_ds> bucket
```
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