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From Artur Siekielski <>
Subject Performance penalty of multiple UPDATEs of non-pk columns
Date Fri, 15 May 2015 09:16:04 GMT
I've seen some discussions about the topic on the list recently, but I 
would like to get more clear answers.

Given the table:

	f1 text,
	f2 text,
	f3 text,
	PRIMARY KEY(f1, f2)

and assuming I will execute UPDATE of f3 multiple times (say, 1000) for 
the same key values k1, k2 and different values of 'newval':

UPDATE t1 SET f3=newval WHERE f1=k1 AND f2=k2;

How will the performance of selecting the current 'f3' value be affected?:

SELECT f3 FROM t1 WHERE f1=k2 AND f2=k2;

It looks like all the previous values are preserved until compaction, 
but does executing the SELECT reads all the values (O(n), n - number of 
updates) or only the current one (O(1)) ?

How the situation looks for Counter types?

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