[#index_util]
= index_util
:mrdocs:

Shared database key types for blockfilterindex and coinstatsindex.

== Description

Index data is usually indexed by height, but in case of a reorg, entries of blocks no longer in the main chain will be copied to a hash index by which they can still be queried. Keys for the height index have the type [DB_BLOCK_HEIGHT, uint32 (BE)]. The height is represented as big‐endian so that sequential reads of filters by height are fast. Keys for the hash index have the type [DB_BLOCK_HASH, uint256].

== Types

[cols="1,4"]
|===
| Name| Description
| xref:index_util/DBHashKey.adoc[`DBHashKey`] 
| Database key for an index entry looked up by block hash.
| xref:index_util/DBHeightKey.adoc[`DBHeightKey`] 
| Database key for an index entry looked up by block height.
|===


== Functions

[cols="1,4"]
|===
| Name| Description
| xref:index_util/CopyHeightIndexToHashIndex.adoc[`CopyHeightIndexToHashIndex`] 
| Copy an index entry from the height index to the hash index.
| xref:index_util/LookUpOne.adoc[`LookUpOne`] 
| Look up a single index entry for a block, trying the height index then the hash index.
|===


== Variables

[cols="1,4"]
|===
| Name| Description
| xref:index_util/DB_BLOCK_HASH.adoc[`DB_BLOCK_HASH`] 
| Key prefix byte identifying an entry in the hash index.
| xref:index_util/DB_BLOCK_HEIGHT.adoc[`DB_BLOCK_HEIGHT`] 
| Key prefix byte identifying an entry in the height index.
|===



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