B-tree

Ordered search

B-trees can handle equality and range queries on data that can be sorted into some ordering. In particular, the PostgreSQL query planner will consider using a B-tree index whenever an indexed column is involved in a comparison using one of these operators:

Reading PostgreSQL 18.6.

Capabilities · PostgreSQL 18.6

These are same-version documentary conclusions. Conditional capabilities depend on the operator class, indexed type or query; they are not universal guarantees.

Capability	Support	Conditions and evidence
Sorted output	Yes	Ordinary sorted output is distinct from ordering by an operator, such as nearest-neighbor distance. Same-version documentation In addition to simply finding the rows to be returned by a query, an index may be able to deliver them in a specific sorted order. This allows a query's ORDER BY specification to be honored without a separate sorting step. Of the index types currently supported by PostgreSQL , only B-tree can produce sorted output — the other index types return matching rows in an unspecified, implementation-dependent order. PostgreSQL 18.6 · indexes-ordering
Unique keys	Yes	This means a unique index. Exclusion constraints use a different contract. Same-version documentation Currently, only B-tree indexes can be declared unique. PostgreSQL 18.6 · indexes-unique
Multiple key columns	Yes	Multiple search keys are distinct from non-key INCLUDE payload columns. Same-version documentation Currently, only the B-tree, GiST, GIN, and BRIN index types support multiple-key-column indexes. Whether there can be multiple key columns is independent of whether INCLUDE columns can be added to the index. Indexes can have up to 32 columns, including INCLUDE columns. (This limit can be altered when building PostgreSQL ; see the file pg_config_manual.h .) PostgreSQL 18.6 · indexes-multicolumn
INCLUDE columns	Yes	Payload columns do not become search keys. Wide payloads can exceed the index tuple-size limit. Same-version documentation Currently, the B-tree, GiST and SP-GiST index access methods support this feature. In these indexes, the values of columns listed in the INCLUDE clause are included in leaf tuples which correspond to heap tuples, but are not included in upper-level index entries used for tree navigation. PostgreSQL 18.6 · sql-createindex
Index-only scans	Yes	The query must use covered values; visibility-map state determines whether heap visits can be avoided. Same-version documentation The index type must support index-only scans. B-tree indexes always do. GiST and SP-GiST indexes support index-only scans for some operator classes but not others. Other index types have no support. The underlying requirement is that the index must physically store, or else be able to reconstruct, the original data value for each index entry. As a counterexample, GIN indexes cannot support index-only scans because each index entry typically holds only part of the original data value. PostgreSQL 18.6 · indexes-index-only-scans
Distance ordering	Not established	Availability depends on the chosen operator class and ordering operator. The sampled source does not establish this capability. This is not a “no”.
Parallel index scan	Yes	A cooperating scan of one index is distinct from a parallel bitmap heap scan or separate serial scans under Parallel Append. Same-version documentation In a parallel index scan or parallel index-only scan , the cooperating processes take turns reading data from the index. Currently, parallel index scans are supported only for btree indexes. Each process will claim a single index block and will scan and return all tuples referenced by that block; other processes can at the same time be returning tuples from a different index block. The results of a parallel btree scan are returned in sorted order within each worker process. PostgreSQL 18.6 · parallel-plans
Parallel index build	Yes	Parallel construction is separate from parallel scans. Worker availability, settings and build phases also matter. Same-version documentation PostgreSQL can build indexes while leveraging multiple CPUs in order to process the table rows faster. This feature is known as parallel index build . For index methods that support building indexes in parallel (currently, B-tree, GIN, and BRIN), maintenance_work_mem specifies the maximum amount of memory that can be used by each index build operation as a whole, regardless of how many worker processes were started. Generally, a cost model automatically determines how many worker processes should be requested, if any. PostgreSQL 18.6 · sql-createindex

Queries, operators and limitations

CREATE INDEX name ON table_name USING btree (column_name);

Syntax template; replace the table and column placeholders with suitable objects and choose a compatible operator class.

<   <=   =   >=   >

Constructs equivalent to combinations of these operators, such as BETWEEN and IN , can also be implemented with a B-tree index search. Also, an IS NULL or IS NOT NULL condition on an index column can be used with a B-tree index.

The optimizer can also use a B-tree index for queries involving the pattern matching operators LIKE and ~ if the pattern is a constant and is anchored to the beginning of the string — for example, col LIKE 'foo%' or col ~ '^foo' , but not col LIKE '%bar' . However, if your database does not use the C locale you will need to create the index with a special operator class to support indexing of pattern-matching queries; see Section 11.10 below. It is also possible to use B-tree indexes for ILIKE and ~* , but only if the pattern starts with non-alphabetic characters, i.e., characters that are not affected by upper/lower case conversion.

B-tree indexes can also be used to retrieve data in sorted order. This is not always faster than a simple scan and sort, but it is often helpful.

Storage options

Set index options with CREATE INDEX … WITH or ALTER INDEX … SET. Defaults and effective behavior depend on the access method and selected PostgreSQL version.

`fillfactor`

Controls how full the index method will try to pack index pages. For B-trees, leaf pages are filled to this percentage during initial index builds, and also when extending the index at the right (adding new largest key values). If pages subsequently become completely full, they will be split, leading to fragmentation of the on-disk index structure. B-trees use a default fillfactor of 90, but any integer value from 10 to 100 can be selected.

B-tree indexes on tables where many inserts and/or updates are anticipated can benefit from lower fillfactor settings at CREATE INDEX time (following bulk loading into the table). Values in the range of 50 - 90 can usefully “ smooth out ” the rate of page splits during the early life of the B-tree index (lowering fillfactor like this may even lower the absolute number of page splits, though this effect is highly workload dependent). The B-tree bottom-up index deletion technique described in Section 65.1.4.2 is dependent on having some “ extra ” space on pages to store “ extra ” tuple versions, and so can be affected by fillfactor (though the effect is usually not significant).

In other specific cases it might be useful to increase fillfactor to 100 at CREATE INDEX time as a way of maximizing space utilization. You should only consider this when you are completely sure that the table is static (i.e. that it will never be affected by either inserts or updates). A fillfactor setting of 100 otherwise risks harming performance: even a few updates or inserts will cause a sudden flood of page splits.

The other index methods use fillfactor in different but roughly analogous ways; the default fillfactor varies between methods.

Same-version option definition

`deduplicate_items`

Controls usage of the B-tree deduplication technique described in Section 65.1.4.3 . Set to ON or OFF to enable or disable the optimization. (Alternative spellings of ON and OFF are allowed as described in Section 19.1 .) The default is ON .

Turning deduplicate_items off via ALTER INDEX prevents future insertions from triggering deduplication, but does not in itself make existing posting list tuples use the standard tuple representation.

Same-version option definition

Version comparison

No differences in documented capability states or storage-option inventory between these samples.

This comparison covers capability states and the names of documented storage options. It does not compare every algorithm, performance characteristic, option definition or release-note change.

Documented history

PostgreSQL 12 → 13

Storage option recorded: deduplicate_items
Storage option no longer recorded: vacuum_cleanup_index_scale_factor

PostgreSQL 10 → 11

INCLUDE columns: No → Yes
Parallel index build: Not established → Yes (source coverage changed)
Storage option recorded: vacuum_cleanup_index_scale_factor

PostgreSQL 9.6 → 10

Parallel index scan: Not established → Yes (source coverage changed)

PostgreSQL 9.5 → 9.6

Index-only scans: Not established → Yes (source coverage changed)

Sources and build identity

Extracted from the loaded English manual build 18.6. No runtime capability measurement is claimed.

Source fingerprints

Manual build: PostgreSQL 18.6 Documentation
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Source archive recorded by the manual manifest: 18.6
Archive SHA-256 recorded by the manual manifest: 555610c24d53e4316da5b7d3fc25c279d96856d5e0e23ee308c328c5fa881d9f

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Back to Index AM · Recorded in PostgreSQL 9.0 through 20; first presence in this sample does not establish first introduction.