sijie commented on a change in pull request #402: Issue 356: Release notes 4.5.0

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+title: Apache BookKeeper 4.5.0 Release Notes
+layout: community
+This is the fifth release of BookKeeper as an Apache Top Level Project!
+The 4.5.0 release incorporates hundreds of new fixes, improvements, and 
features since previous major release, 4.4.0,
+which was released over a year ago. It is a big milestone in Apache BookKeeper 
community, converging from three
+main branches (Salesforce, Twitter and Yahoo).
+Apache BookKeeper users are encouraged to upgrade to `4.5.0`. The technical 
details of this release are summarized
+## Highlights
+The main features in 4.5.0 cover are around four areas:
+- Security
+- Public API
+- Performance
+- Operations
+### Security
+Prior to this release, Apache BookKeeper only supports simple `DIGEST-MD5` 
type authentication.
+With this release of Apache BookKeeper, a number of feature are introduced 
that can be used, together of separately,
+to secure a BookKeeper cluster.
+The following security features are currently supported.
+- Authentication of connections to bookies from clients, using either `TLS` or 
`SASL (Kerberos).
+- Authentication of connections from clients, bookies, autorecovery daemons to 
`ZooKeeper`, when using zookeeper
+    based ledger managers.
+- Encryption of data transferred between bookies and clients, between bookies 
and autorecovery daemons using `TLS`.
+It's worth noting that those security features are optional - non-secured 
clusters are supported, as well as a mix
+of authenticated, unauthenticated, encrypted and non-encrypted clients.
+For more details, have a look at [BookKeeper Security](../security).
+### Public API
+There are multiple new client features introduced in 4.5.0.
+#### LedgerHandleAdv
+The [Ledger API] is the low level API provides by BookKeeper for interacting 
with `ledgers` in a bookkeeper cluster.
+It is simple but not flexible on ledger id or entry id generation. Apache 
BookKeeper introduces `LedgerHandleAdv`
+as an extension of existing `LedgerHandle` for advanced usage. The new 
`LedgerHandleAdv` allows applications providing
+its own `ledger-id` and assigning `entry-id` on adding entries.
+See [Ledger Advanced API](../api/ledger-adv-api) for more details.
+#### Long Poll
+`Long Poll` is a main feature that [DistributedLog]( 
uses to achieve low-latency tailing.
+This big feature has been merged back in 4.5.0 and available to BookKeeper 
users. It allows tailing-reads without
+polling `LastAddConfirmed` everytime after the readers exhaust known entries.
+Although `Long Poll` brings great latency improvements on tailing reads, it is 
still a very low-level primitive.
+It is still recommended to use high level API (e.g. [DistributedLog 
API](../api/distributedlog-api)) for tailing and streaming use cases.
+See [Streaming 
 for more details.
+#### Explicit LAC
+Prior to 4.5.0, the `LAC` is only advanced when subsequent entries are added. 
If there is no subsequent entries added,
+the last entry written will not be visible to readers until the ledger is 
closed. High-level client (e.g. DistributedLog) or applications
+has to work around this by writing some sort of `control records` to advance 
+In 4.5.0, a new `explicit lac` feature is introduced to periodically advance 
`LAC` if there are not subsequent entries added. This feature
+can be enabled by setting `explicitLacInterval` to a positive value.
+### Performance
+There are a lot for performance related bug fixes and improvements in 4.5.0. 
The major performance improvement introduced in 4.5.0, is
 Review comment:
   I added a paragraph at the beginning of `performance` section. 
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