index BRIN BRIN stands for Block Range Index. BRIN is designed for handling very large tables in which certain columns have some natural correlation with their physical location within the table. A block range is a group of pages that are physically adjacent in the table; for each block range, some summary info is stored by the index. For example, a table storing a store's sale orders might have a date column on which each order was placed, and most of the time the entries for earlier orders will appear earlier in the table as well; a table storing a ZIP code column might have all codes for a city grouped together naturally. BRIN indexes can satisfy queries via regular bitmap index scans, and will return all tuples in all pages within each range if the summary info stored by the index is consistent with the query conditions. The query executor is in charge of rechecking these tuples and discarding those that do not match the query conditions — in other words, these indexes are lossy. Because a BRIN index is very small, scanning the index adds little overhead compared to a sequential scan, but may avoid scanning large parts of the table that are known not to contain matching tuples. The specific data that a BRIN index will store, as well as the specific queries that the index will be able to satisfy, depend on the operator class selected for each column of the index. Data types having a linear sort order can have operator classes that store the minimum and maximum value within each block range, for instance; geometrical types might store the bounding box for all the objects in the block range. The size of the block range is determined at index creation time by the pages_per_range storage parameter. The number of index entries will be equal to the size of the relation in pages divided by the selected value for pages_per_range. Therefore, the smaller the number, the larger the index becomes (because of the need to store more index entries), but at the same time the summary data stored can be more precise and more data blocks can be skipped during an index scan. The core PostgreSQL distribution includes the BRIN operator classes shown in . The minmax operator classes store the minimum and the maximum values appearing in the indexed column within the range. Name Indexed Data Type Indexable Operators bytea_minmax_ops bytea < <= = >= > char_minmax_ops "char" < <= = >= > name_minmax_ops name < <= = >= > int8_minmax_ops bigint < <= = >= > int2_minmax_ops smallint < <= = >= > int4_minmax_ops integer < <= = >= > text_minmax_ops text < <= = >= > oid_minmax_ops oid < <= = >= > tid_minmax_ops tid < <= = >= > float4_minmax_ops real < <= = >= > float8_minmax_ops double precision < <= = >= > abstime_minmax_ops abstime < <= = >= > reltime_minmax_ops reltime < <= = >= > macaddr_minmax_ops macaddr < <= = >= > inet_minmax_ops inet < <= = >= > bpchar_minmax_ops character < <= = >= > date_minmax_ops date < <= = >= > time_minmax_ops time without time zone < <= = >= > timestamp_minmax_ops timestamp without time zone < <= = >= > timestamptz_minmax_ops timestamp with time zone < <= = >= > interval_minmax_ops interval < <= = >= > timetz_minmax_ops time with time zone < <= = >= > bit_minmax_ops bit < <= = >= > varbit_minmax_ops bit varying < <= = >= > numeric_minmax_ops numeric < <= = >= > uuid_minmax_ops uuid < <= = >= > pg_lsn_minmax_ops pg_lsn < <= = >= > The BRIN interface has a high level of abstraction, requiring the access method implementer only to implement the semantics of the data type being accessed. The BRIN layer itself takes care of concurrency, logging and searching the index structure. All it takes to get a BRIN access method working is to implement a few user-defined methods, which define the behavior of summary values stored in the index and the way they interact with scan keys. In short, BRIN combines extensibility with generality, code reuse, and a clean interface. There are four methods that an operator class for BRIN must provide: BrinOpcInfo *opcInfo(Oid type_oid) Returns internal information about the indexed columns' summary data. The return value must point to a palloc'd BrinOpcInfo, which has this definition: typedef struct BrinOpcInfo { /* Number of columns stored in an index column of this opclass */ uint16 oi_nstored; /* Opaque pointer for the opclass' private use */ void *oi_opaque; /* Type IDs of the stored columns */ Oid oi_typids[FLEXIBLE_ARRAY_MEMBER]; } BrinOpcInfo; BrinOpcInfo.oi_opaque can be used by the operator class routines to pass information between support procedures during an index scan. bool consistent(BrinDesc *bdesc, BrinValues *column, ScanKey key) Returns whether the ScanKey is consistent with the given indexed values for a range. The attribute number to use is passed as part of the scan key. bool addValue(BrinDesc *bdesc, BrinValues *column, Datum newval, bool isnull) Given an index tuple and an indexed value, modifies the indicated attribute of the tuple so that it additionally represents the new value. If any modification was done to the tuple, true is returned. bool unionTuples(BrinDesc *bdesc, BrinValues *a, BrinValues *b) Consolidates two index tuples. Given two index tuples, modifies the indicated attribute of the first of them so that it represents both tuples. The second tuple is not modified. To implement these methods in a generic way, the operator class defines its own internal support functions. (For instance, min/max operator classes implements support functions for the four inequality operators for the data type.) Additionally, the operator class must supply appropriate operator entries, to enable the optimizer to use the index when those operators are used in queries.