Chapter 64. Index Access Method Interface Definition

Chapter 64. Index Access Method Interface Definition
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Table of Contents

64.1. Basic API Structure for Indexes
64.2. Index Access Method Functions
64.3. Index Scanning
64.4. Index Locking Considerations
64.5. Index Uniqueness Checks
64.6. Index Cost Estimation Functions

+ This chapter defines the interface between the core + PostgreSQL system and index access + methods, which manage individual index types. The core system + knows nothing about indexes beyond what is specified here, so it is + possible to develop entirely new index types by writing add-on code. +

+ All indexes in PostgreSQL are what are known + technically as secondary indexes; that is, the index is + physically separate from the table file that it describes. Each index + is stored as its own physical relation and so is described + by an entry in the pg_class catalog. The contents of an + index are entirely under the control of its index access method. In + practice, all index access methods divide indexes into standard-size + pages so that they can use the regular storage manager and buffer manager + to access the index contents. (All the existing index access methods + furthermore use the standard page layout described in Section 73.6, and most use the same format for index + tuple headers; but these decisions are not forced on an access method.) +

+ An index is effectively a mapping from some data key values to + tuple identifiers, or TIDs, of row versions + (tuples) in the index's parent table. A TID consists of a + block number and an item number within that block (see Section 73.6). This is sufficient + information to fetch a particular row version from the table. + Indexes are not directly aware that under MVCC, there might be multiple + extant versions of the same logical row; to an index, each tuple is + an independent object that needs its own index entry. Thus, an + update of a row always creates all-new index entries for the row, even if + the key values did not change. (HOT + tuples are an exception to this + statement; but indexes do not deal with those, either.) Index entries for + dead tuples are reclaimed (by vacuuming) when the dead tuples themselves + are reclaimed. +

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Chapter 63. Table Access Method Interface Definition	Home	64.1. Basic API Structure for Indexes