WAL

wal package is the basic defination of wal interface of milvus streamingnode. wal use github.com/milvus-io/milvus/pkg/streaming/walimpls to implement the final wal service.

Project arrangement

• wal
  • /: only define exposed interfaces.
  • /adaptor/: adaptors to implement wal interface from walimpls interface
  • /utility/: A utility code for common logic or data structure.
• github.com/milvus-io/milvus/pkg/streaming/walimpls
  • /: define the underlying message system interfaces need to be implemented.
  • /registry/: A static lifetime registry to regsiter new implementation for inverting dependency.
  • /helper/: A utility used to help developer to implement walimpls conveniently.
  • /impls/: A official implemented walimpls sets.

Lifetime Of Interfaces

• OpenerBuilder has a static lifetime in a programs:
• Opener keep same lifetime with underlying resources (such as mq client).
• WAL keep same lifetime with underlying writer of wal, and it's lifetime is always included in related Opener.
• Scanner keep same lifetime with underlying reader of wal, and it's lifetime is always included in related WAL.

Add New Implemetation Of WAL

developper who want to add a new implementation of wal should implements the github.com/milvus-io/milvus/pkg/streaming/walimpls package interfaces. following interfaces is required:

• walimpls.OpenerBuilderImpls
• walimpls.OpenerImpls
• walimpls.ScannerImpls
• walimpls.WALImpls

OpenerBuilderImpls create OpenerImpls; OpenerImpls creates WALImpls; WALImpls create ScannerImpls. Then register the implmentation of walimpls.OpenerBuilderImpls into github.com/milvus-io/milvus/pkg/streaming/walimpls/registry package.

import "github.com/milvus-io/milvus/pkg/streaming/walimpls/registry"

var _ OpenerBuilderImpls = b{};
registry.RegisterBuilder(b{})

All things have been done.

Use WAL

import "github.com/milvus-io/milvus/internal/streamingnode/server/wal/registry"

name := "your builder name"
var yourCh *options.PChannelInfo

opener, err := registry.MustGetBuilder(name).Build()
if err != nil {
    panic(err)
}
ctx := context.Background()
logger, err := opener.Open(ctx, wal.OpenOption{
    Channel: yourCh  
})
if err != nil {
    panic(err)
}

Adaptor

package adaptor is used to adapt walimpls and wal together. common wal function should be implement by it. Such as:

• lifetime management
• interceptor implementation
• scanner wrapped up
• write ahead cache implementation