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From: karanmehta93 <git@git.apache.org>
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Subject: [GitHub] phoenix pull request #277: PHOENIX-3757 System mutex table not being created...
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Message-Id: <20171024211729.20A03DFB0E@git1-us-west.apache.org>
Date: Tue, 24 Oct 2017 21:17:28 +0000 (UTC)
archived-at: Tue, 24 Oct 2017 21:17:32 -0000

Github user karanmehta93 commented on a diff in the pull request:

    https://github.com/apache/phoenix/pull/277#discussion_r146695278
  
    --- Diff: phoenix-core/src/main/java/org/apache/phoenix/coprocessor/MetaDataProtocol.java ---
    @@ -95,6 +97,7 @@
         // Key is the SYSTEM.CATALOG timestamp for the version and value is the version string.
         private static final NavigableMap<Long, String> TIMESTAMP_VERSION_MAP = new TreeMap<>();
         static {
    +        TIMESTAMP_VERSION_MAP.put(MIN_SYSTEM_TABLE_MIGRATION_TIMESTAMP, MIGRATION_IN_PROGRESS);
    --- End diff --
    
    Nope, this one is not only for test. 
    
    When you acquire a lock on SYSMUTEX, the method requires you to pass in a server side timestamp of SYSCAT table (Since it was meant for that earlier) and it checks if the current timestamp is less than the MIN_SYSTEM_TABLE_TIMESTAMP before upgrading it.
    I can't use MIN_SYSTEM_TABLE_TIMESTAMP because then the code for `acquireUpgradeMutex()` wont allow me to acquire the mutex lock.
    I use the same `UpgradeInProgressException` to prevent multiple clients migrating the system tables together. I use this value in `UpgradeInProgressException` to change the error message displayed to the user. 


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