When executing UPDATE or DELETE operations on a table with low cardinality for certain column(s), the operations take a long time though the INSERT operations on those rows ran fast. There is an index on the column in question. The cardinality is a measure of the number of distinct column values as a percentage of all the column values. The higher the cardinality, the more the uniqueness in column value.
A low cardinality can slow down execution.
A low cardinality can slow down UPDATE or DELETE though INSERT is not impacted. This is how Oracle performs fetching of the correct row for UPDATE or DELETE. Before Post can carry out these two types of operation on the target table, it needs to locate the correct row in Oracle. So even though the index exists, the fetching of the correct row will take time due to the low cardinality. Since nothing can be done about the low cardinality (due to the inherent nature of the data), one has to live with this type of performance. Remember that this is not a Post problem but rather a function of Oracle.
