Abstract: A cost based optimizer and a cost estimation method and device. The method includes: in response to deciding that acquired statistical information is incomplete, determining a corresponding cost estimation manner according to an operation type of an operation tree relying on the statistical information (S11); determining a cost estimate of the corresponding operation type based on the cost estimation manner (S12); and determining an accumulative cost estimate of the operation tree according to the cost estimate corresponding to the operation type relying on the statistical information and a cost estimate corresponding to an operation type not relying on the statistical information (S13). Therefore, cost estimation may be performed for a temporary table and a subquery created in a running process, and is not limited by a data scale in a scenario of massive data.

Abstract: An objective of the present application is to provide a method and device for processing a distributed transaction. Compared with the prior art, in a distributed system, a first device in the present application is a group formed by multiple nodes. The first device acquires a writer lock adding request, sent by an SQL compiler, about a target table of a to-be-processed transaction, and performs writer lock adding processing on the target table on the basis of the writer lock adding request, so as to avoid collision problems in multi-transaction concurrence and to ensure isolation of transactions. If the writer lock adding processing is successful, to-be-processed version information of the target table is sent to the SQL compiler, so as to ensure that the SQL compiler operates a correct version of the target table later.