Test TestBigQuery.test_transaction_info is flaky.

[jimfulton]

https://source.cloud.google.com/results/invocations/2ca6ab31-ba0f-4a6b-ab53-55943a5bac42/targets/cloud-devrel%2Fclient-libraries%2Fpython%2Fgoogleapis%2Fpython-bigquery%2Fpresubmit%2Fsystem-3.8/log

This test fails pretty regularly for me.

[tswast]

I checked the job state for a recent failure:

{
 "kind": "bigquery#job",
 "etag": "NSFsBEFD1+My1joEvfuzGQ==",
 "id": "precise-truck-742:US.a9a56a2e-836e-4679-add5-941543bfbf8f",
 "selfLink": "https://content-bigquery.googleapis.com/bigquery/v2/projects/precise-truck-742/jobs/a9a56a2e-836e-4679-add5-941543bfbf8f?location=US",
 "user_email": "REDACTED",
 "configuration": {
 "query": {
 "query": "\n BEGIN TRANSACTION;\n INSERT INTO `precise-truck-742.python_bigquery_tests_system_bq_system_test_1632082968448.test_dml_statistics`\n VALUES (\"one\", 1), (\"two\", 2), (\"three\", 3), (\"four\", 4);\n\n UPDATE `precise-truck-742.python_bigquery_tests_system_bq_system_test_1632082968448.test_dml_statistics`\n SET bar = bar + 1\n WHERE bar \u003e 2;\n COMMIT TRANSACTION;\n ",
 "priority": "INTERACTIVE",
 "useLegacySql": false
 },
 "jobType": "QUERY"
 },
 "jobReference": {
 "projectId": "precise-truck-742",
 "jobId": "a9a56a2e-836e-4679-add5-941543bfbf8f",
 "location": "US"
 },
 "statistics": {
 "creationTime": "1632082969228",
 "startTime": "1632082969269",
 "endTime": "1632082974219",
 "totalBytesProcessed": "55",
 "query": {
 "totalBytesProcessed": "55",
 "totalBytesBilled": "10485760",
 "totalSlotMs": "19050",
 "statementType": "SCRIPT"
 },
 "totalSlotMs": "19050",
 "numChildJobs": "4"
 },
 "status": {
 "state": "DONE"
 }
}

Looks like no transactionInfo key was ever added. I've filed internal issue 200542305 to have the backend team investigate further.

[tswast]

According to the backend folks, since a query job can contain multiple transactions, this key is not intended to be present on the parent job. Instead, we need to iterate through the child jobs to find the one that began the transaction.

They are investigating why transactionInfo appears on the parent job at all (more often than not).

[jimfulton]

Still flaking for me. Was the fix applied to the V3 branch?

https://source.cloud.google.com/results/invocations/9cbcc219-744b-4309-bdde-86aee021f703/targets/cloud-devrel%2Fclient-libraries%2Fpython%2Fgoogleapis%2Fpython-bigquery%2Fpresubmit%2Fprerelease-deps-3.8/log

[plamut]

@jimfulton IIRC not yet, I'm waiting on #855 (pretty large!) to get in before syncing v3 with main (it has been fixed in main, though).

[tswast]

Fixed by #996