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From manjun <manj...@gmail.com>
Subject How Log Roller determines the highest sequence number written to a storage file?
Date Wed, 16 Oct 2013 14:42:16 GMT
Hi,

I was wondering how the last/highest sequence number will be determined if
suppose. 4 edits arrive sequentially at the Hregion which gets routed to
corresponding Hregions. Lets say first two (Edit 1 and edit 2) goes to
region 1. This will write the edits to WAL with sequence number 0 (For edit
1) and 1 (for edit 2). And writes the data into memstore. Imagine the
memstore at region 1 is not full so it won't be flushed. now edits 3 and 4
arrive at region 2 it writes to WAL with sequence number 2 (for edit 3) and
3 (for edit 4) when it writes to memstore imagine the memstore is full so it
gets flushed to disk. 

The questions is:
Now the last written sequence number is 3 so when logroller runs it
determines the highest sequence number pushed to disk is 3 so will it remove
all edits in WAL till 3? I am sure this is not the case since edits 0 and 1
are still in memstore of region 1.

Can somebody explain or correct my understanding of logroller.

Thanks
Manjunath 




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