SymmetricDS Could not communicate with node - Codes Helper - Programming Question Answer

SymmetricDS Could not communicate with node

problem description

using SymmetricDS Synchronize database, the child node will report

Could not communicate with node "law_sys:law_sys_jituan:law_sys_jituan" at http://localhost:8080/sync/law-jituan because of unexpected error
java.util.ConcurrentModificationException
    at java.util.ArrayList$Itr.checkForComodification(Unknown Source)
    at java.util.ArrayList$Itr.next(Unknown Source)
    at org.jumpmind.symmetric.service.impl.OutgoingBatchService.getOutgoingBatches(OutgoingBatchService.java:360)
    at org.jumpmind.symmetric.service.impl.DataExtractorService.extract(DataExtractorService.java:408)
    at org.jumpmind.symmetric.service.impl.PushService.pushToNode(PushService.java:193)
    at org.jumpmind.symmetric.service.impl.PushService.execute(PushService.java:157)
    at org.jumpmind.symmetric.service.impl.NodeCommunicationService$2.run(NodeCommunicationService.java:307)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
    at java.lang.Thread.run(Unknown Source)

occasionally the master node will report

Error while processing GET request for externalId: null, node: proj_sys_xianyi at 127.0.0.1 (127.0.0.1) with path: /law-jituan/pull
SymmetricServlet - java.util.ConcurrentModificationException

but the data can be successful on Synchronize, and we haven"t found that it will affect the normal business for the time being.
Child node problems occasionally occur in PushServer,FileSyncServer and this error must occur, but I do not have any file Synchronize business, nor have I configured it.

the platform version of the problem and what methods you have tried

SymmetricDS 3.6.0
Oracle 11.2
tried to reconfigure, but did not find the problem; tried to change the version, but directly could not start, and others still share a version, so the replacement version is too expensive.

expectation

find the problem and stop reporting errors.

Oracle

Mar.21,2022

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MySQL Query : SELECT * FROM `codeshelper`.`v9_news` WHERE status=99 AND catid='6' ORDER BY rand() LIMIT 5
MySQL Error : Disk full (/tmp/#sql-temptable-64f5-1b36435-2bff0.MAI); waiting for someone to free some space... (errno: 28 "No space left on device")
MySQL Errno : 1021
Message : Disk full (/tmp/#sql-temptable-64f5-1b36435-2bff0.MAI); waiting for someone to free some space... (errno: 28 "No space left on device")
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