13.6. Locking and Indexes

13.6. Locking and Indexes
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+ Though PostgreSQL + provides nonblocking read/write access to table + data, nonblocking read/write access is not currently offered for every + index access method implemented + in PostgreSQL. + The various index types are handled as follows: + +

+ B-tree, GiST and SP-GiST indexes +: + Short-term share/exclusive page-level locks are used for + read/write access. Locks are released immediately after each + index row is fetched or inserted. These index types provide + the highest concurrency without deadlock conditions. +
+ Hash indexes +: + Share/exclusive hash-bucket-level locks are used for read/write + access. Locks are released after the whole bucket is processed. + Bucket-level locks provide better concurrency than index-level + ones, but deadlock is possible since the locks are held longer + than one index operation. +
+ GIN indexes +: + Short-term share/exclusive page-level locks are used for + read/write access. Locks are released immediately after each + index row is fetched or inserted. But note that insertion of a + GIN-indexed value usually produces several index key insertions + per row, so GIN might do substantial work for a single value's + insertion. +

+ Currently, B-tree indexes offer the best performance for concurrent + applications; since they also have more features than hash + indexes, they are the recommended index type for concurrent + applications that need to index scalar data. When dealing with + non-scalar data, B-trees are not useful, and GiST, SP-GiST or GIN + indexes should be used instead. +

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