I'm trying to read bigger collections from Google Firestore for testing and archiving purposes. I'm hitting some interesting errors when I try to get all documents from collections with more than 6k documents in them.

Naive Python solution

My first try was using the Python google-cloud-firestore (version 0.30.0) library.

source_client = firestore.Client()
source = source_client.collection(collection)
source_data = source.get()

counter = 0
for f in source_data:
 app.logger.info(f.id)
 counter += 1
 if counter % 100 == 0:
 app.logger.info('%s %d', datetime.now(), counter)

 app.logger.info('%s Finally read all %d documents', datetime.now(), counter)

Which gives the following output:

INFO:flask.app:2018-11-08 09:49:03.923795 6400 
INFO:flask.app:2018-11-08 09:49:04.115410 6500 
... 
INFO:flask.app:2018-11-08 09:49:03.923795 6400
INFO:flask.app:2018-11-08 09:49:04.115410 6500
WARNING:flask.app:2018-11-08 09:49:04.128478 copy brocken by exception
Traceback (most recent call last):
 File "/home/carsten/projects/transfertool/venv/lib/python3.6/site-packages/flask/app.py", line 2309, in __call__
 return self.wsgi_app(environ, start_response)
 File "/home/carsten/projects/transfertool/venv/lib/python3.6/site-packages/flask/app.py", line 2295, in wsgi_app
 response = self.handle_exception(e)
 File "/home/carsten/projects/transfertool/venv/lib/python3.6/site-packages/flask/app.py", line 1741, in handle_exception
 reraise(exc_type, exc_value, tb)
 File "/home/carsten/projects/transfertool/venv/lib/python3.6/site-packages/flask/_compat.py", line 35, in reraise
 raise value
 File "/home/carsten/projects/transfertool/venv/lib/python3.6/site-packages/flask/app.py", line 2292, in wsgi_app
 response = self.full_dispatch_request()
 File "/home/carsten/projects/transfertool/venv/lib/python3.6/site-packages/flask/app.py", line 1815, in full_dispatch_request
 rv = self.handle_user_exception(e)
 File "/home/carsten/projects/transfertool/venv/lib/python3.6/site-packages/flask/app.py", line 1718, in handle_user_exception
 reraise(exc_type, exc_value, tb)
 File "/home/carsten/projects/transfertool/venv/lib/python3.6/site-packages/flask/_compat.py", line 35, in reraise
 raise value
 File "/home/carsten/projects/transfertool/venv/lib/python3.6/site-packages/flask/app.py", line 1813, in full_dispatch_request
 rv = self.dispatch_request()
 File "/home/carsten/projects/transfertool/venv/lib/python3.6/site-packages/flask/app.py", line 1799, in dispatch_request
 return self.view_functions[rule.endpoint](**req.view_args)
 File "/home/carsten/projects/transfertool/firestore/transfertool/main.py", line 142, in transfer
 count_collection(source_collection)
 File "/home/carsten/projects/transfertool/firestore/transfertool/main.py", line 94, in count_collection
 for f in source_collection.offset(1000).get():
 File "/home/carsten/projects/transfertool/venv/lib/python3.6/site-packages/google/cloud/firestore_v1beta1/query.py", line 588, in get
 for index, response_pb in enumerate(response_iterator):
 File "/home/carsten/projects/transfertool/venv/lib/python3.6/site-packages/google/api_core/grpc_helpers.py", line 83, in next
 six.raise_from(exceptions.from_grpc_error(exc), exc)
 File "<string>", line 3, in raise_from
 # Permission is hereby granted, free of charge, to any person obtaining a copy
google.api_core.exceptions.DeadlineExceeded: 504 Deadline Exceeded

Which seems to be caused by a quota. Even if I cannot see it here. It seems to be time based because when I run with small sleeps in between elements I get less throughput and get the exception after ~50s.

Paging with Python

For exactly this problem there is a paging part in this library. As my application should not care about what kind of data I try to transfer I cannot use the start_after interface but there is still an offset interface with which I can at least read in batches.

for f in source_collection.offset(last_read_offset).get():

Which gives me correct results as long as the last_read_offset is below 1001. If I start with an offset of 1000 I can get results until I get the google.api_core.exceptions.DeadlineExceeded exception from above. But when I start with something bigger I get:

Traceback (most recent call last):
 File "/home/carsten/projects/transfertool/venv/lib/python3.6/site-packages/flask/app.py", line 2309, in __call__
 return self.wsgi_app(environ, start_response)
 File "/home/carsten/projects/transfertool/venv/lib/python3.6/site-packages/flask/app.py", line 2295, in wsgi_app
 response = self.handle_exception(e)
 File "/home/carsten/projects/transfertool/venv/lib/python3.6/site-packages/flask/app.py", line 1741, in handle_exception
 reraise(exc_type, exc_value, tb)
 File "/home/carsten/projects/transfertool/venv/lib/python3.6/site-packages/flask/_compat.py", line 35, in reraise
 raise value
 File "/home/carsten/projects/transfertool/venv/lib/python3.6/site-packages/flask/app.py", line 2292, in wsgi_app
 response = self.full_dispatch_request()
 File "/home/carsten/projects/transfertool/venv/lib/python3.6/site-packages/flask/app.py", line 1815, in full_dispatch_request
 rv = self.handle_user_exception(e)
 File "/home/carsten/projects/transfertool/venv/lib/python3.6/site-packages/flask/app.py", line 1718, in handle_user_exception
 reraise(exc_type, exc_value, tb)
 File "/home/carsten/projects/transfertool/venv/lib/python3.6/site-packages/flask/_compat.py", line 35, in reraise
 raise value
 File "/home/carsten/projects/transfertool/venv/lib/python3.6/site-packages/flask/app.py", line 1813, in full_dispatch_request
 rv = self.dispatch_request()
 File "/home/carsten/projects/transfertool/venv/lib/python3.6/site-packages/flask/app.py", line 1799, in dispatch_request
 return self.view_functions[rule.endpoint](**req.view_args)
 File "/home/carsten/projects/transfertool/firestore/transfertool/main.py", line 144, in transfer
 count_collection(source_collection)
 File "/home/carsten/projects/transfertool/firestore/transfertool/main.py", line 94, in count_collection
 for f in source_collection.offset(1001).get():
 File "/home/carsten/projects/transfertool/venv/lib/python3.6/site-packages/google/cloud/firestore_v1beta1/query.py", line 599, in get
 raise ValueError(msg)
ValueError: Unexpected server response. All responses other than the first must contain a document. The response at index 1 was
read_time 
 seconds: 1541668338
 nanos: 420813000

skipped_results: 1

Looking at the library code it seems that the backend is sending a message which is interpreted as invalid.

Retry via node.js

Okay maybe my code or the Python client library is bugged. Let's try with node.

const admin = require('firebase-admin');
admin.initializeApp(
 credential: admin.credential.applicationDefault()
);

var db = admin.firestore();
admin.firestore().settings( timestampsInSnapshots: true )
var counter = 0

console.log('Read collection')
db.collection(collection).get()
 .then(querySnapshot => 
 querySnapshot.forEach(documentSnapshot => 
 counter++;
 );
 console.log(counter)
 )
 .catch( error => 
 console.log(error)
);

Which does the same as the python library even if the timeout is much more clearly 60s.

[2018-11-09T08:36:30.992Z] App listening on port 8080
[2018-11-09T08:36:30.993Z] Press Ctrl+C to quit.
[2018-11-09T08:36:37.390Z] Read collection
[2018-11-09T08:37:37.406Z] Error: 4 DEADLINE_EXCEEDED: Deadline Exceeded
 at Object.exports.createStatusError (/home/carsten/projects/node_modules/grpc/src/common.js:87:15)
 at ClientReadableStream._emitStatusIfDone (/home/carsten/projects/node_modules/grpc/src/client.js:235:26)
 at ClientReadableStream._readsDone (/home/carsten/projects/node_modules/grpc/src/client.js:201:8)
 at /home/carsten/projects/node_modules/grpc/src/client_interceptors.js:679:15
 code: 4,
 metadata: Metadata _internal_repr: ,
 details: 'Deadline Exceeded' 

Has anyone similar experiences or a good hint how to continue?

PS: The exportDocument / importDocument interface is not enough as we sometimes have to adjust the data after reading. And I have no clue what kind of format Firestore is exporting to Google Cloud Storage or how to transform it.

Edit: golang

And for the heck of it i tried the golang api.

log.Println("Collecting data")
snapshotIter := client.Collection(collection.(string)).Documents(ctx)
defer snapshotIter.Stop()

if err != nil 
 log.Fatalln(err)


i := 0

for 
 _, err := snapshotIter.Next()

 if err == iterator.Done 
 break
 
 if err != nil 
 log.Fatalln(err)
 

 if i % 100 == 0
 log.Println(i)
 
 i++


log.Println("Done")

Which runs into the same timeout as expected.

2018/11/12 15:01:20 Collecting data
2018/11/12 15:01:21 0
2018/11/12 15:01:21 100
2018/11/12 15:01:21 200
2018/11/12 15:01:21 300
2018/11/12 15:01:21 400
2018/11/12 15:01:22 500
2018/11/12 15:01:22 600
2018/11/12 15:01:22 700
....
2018/11/12 15:02:22 29800
2018/11/12 15:02:23 29900
2018/11/12 15:02:23 rpc error: code = DeadlineExceeded desc = The datastore operation timed out, or the data was temporarily unavailable.

But in addition the offset is working fine:

snapshotIter := client.Collection(collection.(string)).Offset(30000).Documents(ctx)