[#BaseIndex-DB]
= xref:BaseIndex.adoc[BaseIndex]::DB
:relfileprefix: ../
:mrdocs:

The database stores a block locator of the chain the database is synced to so that the index can efficiently determine the point it last stopped at. A locator is used instead of a simple hash of the chain tip because blocks and block index entries may not be flushed to disk until after this database is updated.

== Synopsis

Declared in `<index/base.h>`

[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
class DB
    : public xref:CDBWrapper.adoc[CDBWrapper]
----

== Base Classes

[cols="1,4"]
|===
| Name| Description
| `xref:CDBWrapper.adoc[CDBWrapper]`
| Wraps a LevelDB database, providing typed, serialized key‐value access.
|===

== Member Functions

[cols="1,4"]
|===
| Name| Description
| xref:BaseIndex/DB/2constructor.adoc[`DB`]         [.small]#[constructor]#
| Open the index database at the given path.
| xref:BaseIndex/DB/2destructor.adoc[`~DB`] [.small]#[destructor]# [.small]#[virtual]#
| Close the database and release its resources.
| xref:CDBWrapper/operator_assign.adoc[`operator=`]  [.small]#[deleted]#
| Copy assignment is disabled.
| xref:CDBWrapper/CompactFull.adoc[`CompactFull`] 
| Perform a blocking full compaction of the underlying LevelDB.
| xref:CDBWrapper/DynamicMemoryUsage.adoc[`DynamicMemoryUsage`] 
| Get an estimate of LevelDB memory usage (in bytes).
| xref:CDBWrapper/Erase.adoc[`Erase`] 
| Removes the value stored under the given key.
| xref:CDBWrapper/EstimateSize.adoc[`EstimateSize`] 
| Estimates the on‐disk size of the entries in the given key range.
| xref:CDBWrapper/Exists.adoc[`Exists`] 
| Checks whether a value is stored under the given key.
| xref:CDBWrapper/GetProperty.adoc[`GetProperty`] 
| Return a LevelDB property value, if available.
| xref:CDBWrapper/IsEmpty.adoc[`IsEmpty`] 
| Return true if the database managed by this class contains no entries.
| xref:CDBWrapper/NewIterator.adoc[`NewIterator`] 
| Creates a new iterator over the database. The caller owns the returned iterator.
| xref:CDBWrapper/Read.adoc[`Read`] 
| Reads and de‐obfuscates the value stored under the given key.
| xref:BaseIndex/DB/ReadBestBlock.adoc[`ReadBestBlock`]  [.small]#[virtual]#
| Read block locator of the chain that the index is in sync with. Note, the returned locator will be empty if no record exists.
| xref:CDBWrapper/Write.adoc[`Write`] 
| Writes a single key‐value pair to the database.
| xref:CDBWrapper/WriteBatch.adoc[`WriteBatch`] 
| Atomically applies all writes and erases queued in a batch.
| xref:BaseIndex/DB/WriteBestBlock.adoc[`WriteBestBlock`]  [.small]#[virtual]#
| Write block locator of the chain that the index is in sync with.
|===


== Static Member Functions

[cols="1,4"]
|===
| Name| Description
| xref:CDBWrapper/HasKeyStartingWith.adoc[`HasKeyStartingWith`] 
| Probe an unopened database for a key prefix. Return true if a database at path exists and contains at least 1 entry beginning with prefix; missing or empty databases return false, and database errors throw dbwrapper_error.
|===


== Non-Member Functions

[cols="1,4"]
|===
| Name| Description
| xref:dbwrapper_private/GetObfuscation.adoc[`::dbwrapper_private::GetObfuscation`]
| Work around circular dependency, as well as for testing in dbwrapper_tests. Database obfuscation should be considered an implementation detail of the specific database.
| xref:index_util/LookUpOne.adoc[`::index_util::LookUpOne`]
| Look up a single index entry for a block, trying the height index then the hash index.
|===


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