RaigorJiang opened a new issue #12806:
URL: https://github.com/apache/shardingsphere/issues/12806
## Bug Report
### Which version of ShardingSphere did you use?
ShardingSphere-Proxy 5.0.0-RC1 : master branch
### Reason analyze (If you can)
Error log:
```
java.util.ConcurrentModificationException: null
at
java.util.LinkedHashMap$LinkedHashIterator.nextNode(LinkedHashMap.java:719)
at
java.util.LinkedHashMap$LinkedKeyIterator.next(LinkedHashMap.java:742)
at
java.util.AbstractCollection.finishToArray(AbstractCollection.java:232)
at java.util.AbstractCollection.toArray(AbstractCollection.java:143)
at java.util.ArrayList.<init>(ArrayList.java:178)
at
org.apache.shardingsphere.proxy.backend.context.ProxyContext.getAllSchemaNames(ProxyContext.java:98)
at
org.apache.shardingsphere.proxy.backend.text.database.CreateDatabaseBackendHandler.check(CreateDatabaseBackendHandler.java:46)
at
org.apache.shardingsphere.proxy.backend.text.database.CreateDatabaseBackendHandler.execute(CreateDatabaseBackendHandler.java:38)
```
The reason is that the structure of metaDataMap is `LinkedHashMap`. If other
threads modify the data during iteration, an exception will be thrown.
### Steps to reproduce the behavior, such as: SQL to execute, sharding rule
configuration, when exception occur etc.
Execute the following script to quickly create databases:
```bash
#!/bin/bash
PROXY="mysql -uroot -proot -h127.0.0.1 -P3307"
for i in {10..1000}
do
${PROXY} -e "CREATE SCHEMA IF NOT EXISTS sharding_test_${i}_db;"
done
```
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