• Created by Unknown User (eolivelli), last updated on Sep 01, 2017 2 minute read

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Motivation

Currently (in BookKeeper 4.5) we have several overloaded versions of the methods createLedger/createLedegerAdv/asyncCreateLeader/asyncCreateLeaderAdv. This methods are present because from version to version we added new configuration options for the Ledger.

In order to support new features in the future we need to have a more extensible API.

Proposed Change

We can use the Builder design pattern to define a new unified createLedger and asyncCreateLedger API.

This is an example of the new API

        BookKeeper bookeeper = ....;
        LedgerConfiguration ledgerConfiguration = LedgerConfiguration.builder()
                                                                              .ensembleSize(3)
                                                                              .writeQuorumSize(2)
                                                                              .ackQuorumSize(1)
                                                                              .digestType(DigestType.CRC32)                                       
																			  .customMetadata(Map<String, byte[]> metadata)
                                                                              .password(password)
                                                                              .advanced(true|false);
        LedgerHandle ledger = bookeeper.createLedger(ledgerConfiguration);
        bookeeper.createLedgerAsync(ledgerConfiguration, createCallback,  ctx);
        CompletableFuture<LedgerHandle> future = bookeeper.asyncCreateLedger(ledgerConfiguration);

 

So we will introduce a new LedgerConfiguration class which defines the configuration options of the Ledger and we will support a new simple API which takes that structure.

Existing API will be supported, and maybe it will be deprecated and finally dropped in new major releases (5.0.0)

New or Changed Public Interfaces

We are going to introduce the LedgerConfiguration class which defines the specification for new ledgers.

public final LedgerConfiguration  {    
               private final int ensembleSize = 1;
               private final int writeQuorumSize = 1;
               private final int ackQuorumSize = 1;
               private final DigestType digestType = DigestType.CRC32;
               private final byte[] password = EMPTY_ARRAY;
               private final boolean advanced = false;
               private final Map<String, byte[]> customMetadata = null;   (will be an un-modifiable Map)
               /**
               * Create a new LedgerConfiguration with default values

               **/

               public static Builder builder() { return new Builder(); }
               /**
               * Create a new LedgerConfiguration using another configuration as starting values

               **/

              public static Builder cloning(LedgerConfiguration configuration) {......}

              public static final class Builder() {
                         ... builder methods...
                         public LedgerConfiguration build() throws BKException;

              } 
}

 

This new class will be immutable and it will provide only getters.

On BookKeeper class we are going to introduce this new methods

public LedgerHandle createLedger(LedgerConfiguration ledgerConfiguration);

public void asyncCreateLedger(LedgerConfiguration ledgerConfiguration, CreateCallback callback, Object context);

public CompletableFuture<LedgerHandle> asyncCreateLedger(LedgerConfiguration ledgerConfiguration);

 

Migration Plan and Compatibility

No issue about migration and compatibility.

Legacy methods will be retained. No @Deprecated annotation will be added. Futher removal of existing APIs will be evaluated in the future, maybe while starting a new major release, like 5.0.0

Rejected Alternatives

An alternative is not to explicitly add a LedgerConfiguration class but to add some builder method to the BookKeper class, like

BookKeeper bookkeeper =.....;
CompletableFuture<LedgerHandle> lh = bookkeeper.newLedgerBuilder()
                                               .ensembleSize(5)
                                               .createLedger();

 

 

Having a LedgerConfiguration explicit object will be more efficient at runtime as the same object can be reused.

 

 

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