clarify which flags are used for get_or_put methods

heed/src/database.rs

@@ -1997,7 +1997,9 @@ impl<KC, DC, C> Database<KC, DC, C> {
  }
 
  /// Attempt to insert a key-value pair in this database, or if a value already exists for the
- /// key, returns the previous value. The entry is written with no specific flag.
+ /// key, returns the previous value.
+ ///
+ /// The entry is always written with the [`NO_OVERWRITE`](PutFlags::NO_OVERWRITE) flag.
  ///
  /// ```
  /// # use heed::EnvOpenOptions;
@@ -2041,7 +2043,10 @@ impl<KC, DC, C> Database<KC, DC, C> {
  }
 
  /// Attempt to insert a key-value pair in this database, or if a value already exists for the
- /// key, returns the previous value. The entry is written with the specified flags.
+ /// key, returns the previous value.
+ ///
+ /// The entry is written with the specified flags, in addition to
+ /// [`NO_OVERWRITE`](PutFlags::NO_OVERWRITE) which is always used.
  ///
  /// ```
  /// # use heed::EnvOpenOptions;
@@ -2113,7 +2118,8 @@ impl<KC, DC, C> Database<KC, DC, C> {
  /// Attempt to insert a key-value pair in this database, where the value can be directly
  /// written to disk, or if a value already exists for the key, returns the previous value.
  ///
- /// The entry is written with no specific flags.
+ /// The entry is always written with the [`NO_OVERWRITE`](PutFlags::NO_OVERWRITE) and
+ /// [`MDB_RESERVE`](lmdb_master_sys::MDB_RESERVE) flags.
  ///
  /// ```
  /// # use heed::EnvOpenOptions;
@@ -2175,7 +2181,9 @@ impl<KC, DC, C> Database<KC, DC, C> {
  /// Attempt to insert a key-value pair in this database, where the value can be directly
  /// written to disk, or if a value already exists for the key, returns the previous value.
  ///
- /// The entry is written with the specified flags.
+ /// The entry is written with the specified flags, in addition to
+ /// [`NO_OVERWRITE`](PutFlags::NO_OVERWRITE) and [`MDB_RESERVE`](lmdb_master_sys::MDB_RESERVE)
+ /// which are always used.
  ///
  /// ```
  /// # use heed::EnvOpenOptions;