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For SQL Server: But what's about single statements? In SQL Server, there is 4 transaction isolation levels (in pessimistic locking model). Default transaction isolation level is Read Committed, and locks are placed on a statement level. If you have a transaction that has 2 statements inside it that retrieve same data, and in the middle of that ...


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Serializable means that there is some order the transactions can be run in without overlapping and we'll end up with the same answers and the same state of the data base as we get by running the transactions in parallel with serializable isolation level. Given two transactions, A and B, the only valid states of the system are All of A followed by all of B, ...


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Somehow maintainance_work_mem is not considered as maintenance operations and it does not have any implication to speed up the drop index process. Dropping the index concurrently seems to be the only option but I won't suggest to directly run it from Pgadmin or Psql terminal. Because if the session gets terminated or due to timeout, it may leave index ...


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The problem is that there could be values present at the end of A's transaction - the ones inserted by B - that were not present when A first checked. This is known as a phantom A phantom is a row that matches the search criteria but is not initially seen. The way to prevent phantoms is to use the Serializable isolation level. This is the only isolation ...


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