[Backport] Fix cool nested column bug caused by not properly validating that global id is present in global dictionary before lookup local id (#13561)#13572
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kfaraz merged 1 commit intoapache:25.0.0from Dec 16, 2022
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…bal id is present in global dictionary before lookup up local id (apache#13561) This commit fixes a bug with nested column "value set" indexes caused by not properly validating that the globalId looked up for value is present in the global dictionary prior to looking it up in the local dictionary, which when "adjusting" the global ids for value type can cause incorrect selection of value indexes. To use an example of a variant typed nested column with 3 values `["1", null, -2]`. The string dictionary is `[null, "1"]`, the long dictionary is `[-2]` and our local dictionary is `[0, 1, 2]`. The code for variant typed indexes checks if the value is present in all global dictionaries and returns indexes for all matches. So in this case, we first lookup "1" in the string dictionary, find it at global id 1, all is good. Now, we check the long dictionary for `1`, which due to `-(insertionpoint + 1)` gives us `-(1 + 2) = -2`. Since the global id space is actually stacked dictionaries, global ids for long and double values must be "adjusted" by the size of string dictionary, and size of string + size of long for doubles. Prior to this patch we were not checking that the globalId is 0 or larger, we then immediately looked up the `localDictionary.indexOf(-2 + adjustLong) = localDictionary.indexOf(-2 + 2) = localDictionary.indexOf(0)` ... which is an actual value contained in the dictionary! The fix is to skip the longs completely since there were no global matches. On to doubles, `-(insertionPoint + 1)` gives us `-(0 + 1) = -1`. The double adjust value is '3' since 2 strings and 1 long, so `localDictionary.indexOf(-1 + 3)` = `localDictionary.indexOf(2)` which is also a real value in our local dictionary that is definitely not '1'. So in this one case, looking for '1' incorrectly ended up matching every row.
clintropolis
approved these changes
Dec 15, 2022
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Backports #13561