Not exactly so. When index key is not changed by UPDATE statement,
engine doesn't
add it into the index.
Ok, so it has not changed.
tx1: insert record (r1) with index key (k1)
>> table contains one record version: r1-tx1
>> index contains one entry: (k2, r1)
tx1: commit
tx2: update r1 set key = k2
>> table contains two records versions: r1-tx2, r1-tx1
>> index contains two entries: (k1, r1), (k2, r1)
tx2: commit
garbage collector:
>> remove from disk r1-tx1,
>> build lists: staying (r1-tx2), going (r1-tx1)
>> going to cleanup indices
>> context switch...
>> table: r1-2
>> index: (k1, r1), (k2, r1)
tx3: update r1 set key = k1
>> table: r1-tx3, r1-tx2
>> index: (k1, r1), (k2, r1)
note, tx3 doesn't add index entry (k1, r1) as it is already present
tx3: commit
garbage collector:
>> ...continue to cleanup indices
>> lists: staying (r1-tx2), going (r1-tx1)
>> keys: staying (k2), going (k1)
>> remove index key (k1, r1)
On disk
>> table: r1-tx3, r1-tx2
>> index: (k2, r1)
r1-tx3 contains key = k1, but index have no such entry
Very informative, thank you very much.
Above describe the problem, but how it was fixed after FB2 that we have now
this issue?
regards,
Karol Bieniaszewski
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