MappedFile May cause message loss

[kingjames223]

I'm king,In the store module，MappedFile.java at flush.
disk or storage failure (such as the very common file system read only), and the client still thinks that the transmission is normal. Until we found that the disk failure to restart the machine, because the message did not write successfully, and then the message was lost.

[francisoliverlee]

i think so some message may lost casuse of power-off. messages can flush to disk synchronily by set

• message property: MessageConst.PROPERTY_WAIT_STORE_MSG_OK to true
• broker config : flushDiskType=FlushDiskType.SYNC_FLUSH

POOR PERFORMANCE also

code here:

rocketmq/store/src/main/java/org/apache/rocketmq/store/CommitLog.java

Line 957 in df1d93f

if (FlushDiskType.SYNC_FLUSH == this.defaultMessageStore.getMessageStoreConfig().getFlushDiskType()) {