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Please provide as much information as possible. At least, this should include a description of your issue and steps to reproduce the problem. If possible please provide a summary of what steps or workarounds you have already tried, and any docs or articles you found (un)helpful.

Problem you have encountered:
If I have a Mutations groups that exceed mutation limits as per[1] and I issued two or more mutations in the MutationsGroups in BatchWrite API, it got stuck.

What you expected to happen:
Immediately return "Too many mutations..." error.

Steps to reproduce:
1. Create a table, and indexes.
2. Insert record into the table, above some numbers that exceed mutation limits.
3. Issue BatchWrite API with two or more mutations, and one of them will cause exceeding mutation limits.

Other information (workarounds you have tried, documentation consulted, etc):
[1]
https://cloud.google.com/spanner/quotas#limits-for