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From Edmon Begoli <>
Subject Re: Robustness of MemTable
Date Mon, 30 Jul 2012 19:36:26 GMT
Thanks. This is great to know.

On Mon, Jul 30, 2012 at 3:33 PM, Eric Newton <> wrote:
> Yes, the key/value pairs are replicated in redundant logs on other machines.
> We run long tests in which we ingest data and kill random servers;
> this mechanism is robust up to the point to which it is configured.
> That is, if you lose the right number of machines, you will not be
> able to recover the in-memory data.  The default number of node
> failures needed to prevent recovery is 2, though this can be changed
> by configuration.
> -Eric
> On Mon, Jul 30, 2012 at 3:19 PM, Edmon Begoli <> wrote:
>> What is the redundancy/recovery mechanism of Write-Ahead Log and MemTable.
>> I am specifically asking about this statement and the parts about:
>> "When a write arrives at a TabletServer it is written to a Write-Ahead
>> Log and then inserted into a sorted data structure in memory called a
>> MemTable.
>> ...
>> If a TabletServer fails, the Master detects it and automatically
>> reassigns the tablets assigned from the failed server to other
>> servers.
>> Any key-value pairs that were in memory at the time the TabletServer
>> are automatically reapplied from the Write-Ahead Log to prevent any
>> loss of data."
>> I.e. what happens if machine holding a MemTable crashes. Will
>> key-value pairs that we in memory have been replicated already?
>> Thank you,
>> Edmon

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