kv

package
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 Go to latest Published: Sep 20, 2016 License: Apache-2.0 Imports: 37 Imported by: 0

Documentation

Overview

Package kv provides a key-value API to an underlying cockroach datastore. Cockroach itself provides a single, monolithic, sorted key value map, distributed over multiple nodes. Each node holds a set of key ranges. Package kv translates between the monolithic, logical map which Cockroach clients experience to the physically distributed key ranges which comprise the whole.

Package kv implements the logic necessary to locate appropriate nodes based on keys being read or written. In some cases, requests may span a range of keys, in which case multiple RPCs may be sent out.

Index

Constants

This section is empty.

Variables

This section is empty.

Functions

func InitSenderForLocalTestCluster 

func InitSenderForLocalTestCluster(
	nodeDesc *roachpb.NodeDescriptor,
	tracer opentracing.Tracer,
	clock *hlc.Clock,
	latency time.Duration,
	stores client.Sender,
	stopper *stop.Stopper,
	gossip *gossip.Gossip,
) client.Sender

InitSenderForLocalTestCluster initializes a TxnCoordSender that can be used with LocalTestCluster.

Types

type BatchCall 

type BatchCall struct {
	Reply *roachpb.BatchResponse
	Err   error
}

BatchCall contains a response and an RPC error (note that the response contains its own roachpb.Error, which is separate from BatchCall.Err), and is analogous to the net/rpc.Call struct.

type DBServer 

type DBServer struct {
	// contains filtered or unexported fields
}

A DBServer provides an HTTP server endpoint serving the key-value API. It accepts either JSON or serialized protobuf content types.

func NewDBServer 

func NewDBServer(ctx *base.Context, sender client.Sender, stopper *stop.Stopper) *DBServer

NewDBServer allocates and returns a new DBServer.

func (*DBServer) Batch 

func (s *DBServer) Batch(
	ctx context.Context, args *roachpb.BatchRequest,
) (br *roachpb.BatchResponse, err error)

Batch implements the roachpb.KVServer interface.

type DistSender 

type DistSender struct {
	// Ctx is the "base context" for DistSender, used for log messages that are
	// not associated with a more specific request context. It also holds the
	// Tracer that should be used.
	Ctx context.Context
	// contains filtered or unexported fields
}

A DistSender provides methods to access Cockroach's monolithic, distributed key value store. Each method invocation triggers a lookup or lookups to find replica metadata for implicated key ranges. RPCs are sent to one or more of the replicas to satisfy the method invocation.

func NewDistSender 

func NewDistSender(cfg *DistSenderConfig, g *gossip.Gossip) *DistSender

NewDistSender returns a batch.Sender instance which connects to the Cockroach cluster via the supplied gossip instance. Supplying a DistSenderContext or the fields within is optional. For omitted values, sane defaults will be used.

func (*DistSender) CountRanges 

func (ds *DistSender) CountRanges(rs roachpb.RSpan) (int64, error)

CountRanges returns the number of ranges that encompass the given key span.

func (*DistSender) FirstRange 

func (ds *DistSender) FirstRange() (*roachpb.RangeDescriptor, error)

FirstRange implements the RangeDescriptorDB interface. FirstRange returns the RangeDescriptor for the first range on the cluster, which is retrieved from the gossip protocol instead of the datastore.

func (*DistSender) RangeLookup 

func (ds *DistSender) RangeLookup(
	key roachpb.RKey, desc *roachpb.RangeDescriptor, considerIntents, useReverseScan bool,
) ([]roachpb.RangeDescriptor, []roachpb.RangeDescriptor, *roachpb.Error)

RangeLookup implements the RangeDescriptorDB interface. RangeLookup dispatches a RangeLookup request for the given metadata key to the replicas of the given range. Note that we allow inconsistent reads when doing range lookups for efficiency. Getting stale data is not a correctness problem but instead may infrequently result in additional latency as additional range lookups may be required. Note also that rangeLookup bypasses the DistSender's Send() method, so there is no error inspection and retry logic here; this is not an issue since the lookup performs a single inconsistent read only.

func (*DistSender) Send 

func (ds *DistSender) Send(ctx context.Context, ba roachpb.BatchRequest) (*roachpb.BatchResponse, *roachpb.Error)

Send implements the batch.Sender interface. It subdivides the Batch into batches admissible for sending (preventing certain illegal mixtures of requests), executes each individual part (which may span multiple ranges), and recombines the response. When the request spans ranges, it is split up and the corresponding ranges queried serially, in ascending order. In particular, the first write in a transaction may not be part of the first request sent. This is relevant since the first write is a BeginTransaction request, thus opening up a window of time during which there may be intents of a transaction, but no entry. Pushing such a transaction will succeed, and may lead to the transaction being aborted early.

type DistSenderConfig 

type DistSenderConfig struct {
	// Base context for the DistSender. The context can have a Tracer set. If nil,
	// context.Background() will be used.
	Ctx context.Context

	Clock                    *hlc.Clock
	RangeDescriptorCacheSize int32
	// RangeLookupMaxRanges sets how many ranges will be prefetched into the
	// range descriptor cache when dispatching a range lookup request.
	RangeLookupMaxRanges int32
	LeaseHolderCacheSize int32
	RPCRetryOptions      *retry.Options

	// The RPC dispatcher. Defaults to grpc but can be changed here for testing
	// purposes.
	TransportFactory  TransportFactory
	RPCContext        *rpc.Context
	RangeDescriptorDB RangeDescriptorDB
	SendNextTimeout   time.Duration
	// contains filtered or unexported fields
}

DistSenderConfig holds configuration and auxiliary objects that can be passed to NewDistSender.

type RangeDescriptorDB 

type RangeDescriptorDB interface {
	// rangeLookup takes a meta key to look up descriptors for, for example
	// \x00\x00meta1aa or \x00\x00meta2f. The two booleans are considerIntents
	// and useReverseScan respectively. Two slices of range descriptors are
	// returned. The first of these slices holds descriptors which contain
	// the given key (possibly from intents), and the second being prefetched
	// adjacent descriptors.
	// TODO(andrei): Should this return error instead of pErr?
	RangeLookup(
		key roachpb.RKey, desc *roachpb.RangeDescriptor,
		considerIntents bool, useReverseScan bool,
	) ([]roachpb.RangeDescriptor, []roachpb.RangeDescriptor, *roachpb.Error)
	// FirstRange returns the descriptor for the first Range. This is the
	// Range containing all \x00\x00meta1 entries.
	FirstRange() (*roachpb.RangeDescriptor, error)
}

RangeDescriptorDB is a type which can query range descriptors from an underlying datastore. This interface is used by rangeDescriptorCache to initially retrieve information which will be cached.

type ReplicaInfo 

type ReplicaInfo struct {
	roachpb.ReplicaDescriptor
	NodeDesc *roachpb.NodeDescriptor
}

ReplicaInfo extends the Replica structure with the associated node descriptor.

type ReplicaSlice 

type ReplicaSlice []ReplicaInfo

A ReplicaSlice is a slice of ReplicaInfo.

func (ReplicaSlice) FindReplica 

func (rs ReplicaSlice) FindReplica(storeID roachpb.StoreID) int

FindReplica returns the index of the replica which matches the specified store ID. If no replica matches, -1 is returned.

func (ReplicaSlice) FindReplicaByNodeID 

func (rs ReplicaSlice) FindReplicaByNodeID(nodeID roachpb.NodeID) int

FindReplicaByNodeID returns the index of the replica which matches the specified node ID. If no replica matches, -1 is returned.

func (ReplicaSlice) MoveToFront 

func (rs ReplicaSlice) MoveToFront(i int)

MoveToFront moves the replica at the given index to the front of the slice, keeping the order of the remaining elements stable. The function will panic when invoked with an invalid index.

func (ReplicaSlice) Shuffle 

func (rs ReplicaSlice) Shuffle()

Shuffle randomizes the order of the replicas.

func (ReplicaSlice) SortByCommonAttributePrefix 

func (rs ReplicaSlice) SortByCommonAttributePrefix(attrs []string) int

SortByCommonAttributePrefix rearranges the ReplicaSlice by comparing the attributes to the given reference attributes. The basis for the comparison is that of the common prefix of replica attributes (i.e. the number of equal attributes, starting at the first), with a longer prefix sorting first. The number of attributes successfully matched to at least one replica is returned (hence, if the return value equals the length of the ReplicaSlice, at least one replica matched all attributes).

func (ReplicaSlice) Swap 

func (rs ReplicaSlice) Swap(i, j int)

Swap interchanges the replicas stored at the given indices.

type SendOptions 

type SendOptions struct {

	// SendNextTimeout is the duration after which RPCs are sent to
	// other replicas in a set.
	SendNextTimeout time.Duration
	// contains filtered or unexported fields
}

A SendOptions structure describes the algorithm for sending RPCs to one or more replicas, depending on error conditions and how many successful responses are required.

type Transport 

type Transport interface {
	// IsExhausted returns true if there are no more replicas to try.
	IsExhausted() bool

	// SendNext sends the rpc (captured at creation time) to the next
	// replica. May panic if the transport is exhausted. Should not
	// block; the transport is responsible for starting other goroutines
	// as needed.
	SendNext(chan<- BatchCall)

	// Close is called when the transport is no longer needed. It may
	// cancel any pending RPCs without writing any response to the channel.
	Close()
}

Transport objects can send RPCs to one or more replicas of a range. All calls to Transport methods are made from a single thread, so Transports are not required to be thread-safe.

type TransportFactory 

type TransportFactory func(
	SendOptions, *rpc.Context, ReplicaSlice, roachpb.BatchRequest,
) (Transport, error)

TransportFactory encapsulates all interaction with the RPC subsystem, allowing it to be mocked out for testing. The factory function returns a Transport object which is used to send the given arguments to one or more replicas in the slice.

In addition to actually sending RPCs, the transport is responsible for ordering replicas in accordance with SendOptions.Ordering and transport-specific knowledge such as connection health or latency.

TODO(bdarnell): clean up this crufty interface; it was extracted verbatim from the non-abstracted code.

func SenderTransportFactory 

func SenderTransportFactory(tracer opentracing.Tracer, sender client.Sender) TransportFactory

SenderTransportFactory wraps a client.Sender for use as a KV Transport. This is useful for tests that want to use DistSender without a full RPC stack.

type TxnCoordSender 

type TxnCoordSender struct {
	syncutil.Mutex // protects txns and txnStats
	// contains filtered or unexported fields
}

A TxnCoordSender is an implementation of client.Sender which wraps a lower-level Sender (either a storage.Stores or a DistSender) to which it sends commands. It acts as a man-in-the-middle, coordinating transaction state for clients. After a transaction is started, the TxnCoordSender starts asynchronously sending heartbeat messages to that transaction's txn record, to keep it live. It also keeps track of each written key or key range over the course of the transaction. When the transaction is committed or aborted, it clears accumulated write intents for the transaction.

func NewTxnCoordSender 

func NewTxnCoordSender(
	ctx context.Context,
	wrapped client.Sender,
	clock *hlc.Clock,
	linearizable bool,
	stopper *stop.Stopper,
	txnMetrics TxnMetrics,
) *TxnCoordSender

NewTxnCoordSender creates a new TxnCoordSender for use from a KV distributed DB instance. ctx is the base context and is used for logs and traces when there isn't a more specific context available; it must have a Tracer set.

func (*TxnCoordSender) Send 

func (tc *TxnCoordSender) Send(ctx context.Context, ba roachpb.BatchRequest) (*roachpb.BatchResponse, *roachpb.Error)

Send implements the batch.Sender interface. If the request is part of a transaction, the TxnCoordSender adds the transaction to a map of active transactions and begins heartbeating it. Every subsequent request for the same transaction updates the lastUpdate timestamp to prevent live transactions from being considered abandoned and garbage collected. Read/write mutating requests have their key or key range added to the transaction's interval tree of key ranges for eventual cleanup via resolved write intents; they're tagged to an outgoing EndTransaction request, with the receiving replica in charge of resolving them.

type TxnMetrics 

type TxnMetrics struct {
	Aborts     metric.Rates
	Commits    metric.Rates
	Commits1PC metric.Rates // Commits which finished in a single phase
	Abandons   metric.Rates
	Durations  metric.Histograms

	// Restarts is the number of times we had to restart the transaction.
	Restarts *metric.Histogram
}

TxnMetrics holds all metrics relating to KV transactions.

func MakeTxnMetrics 

func MakeTxnMetrics() TxnMetrics

MakeTxnMetrics returns a TxnMetrics struct that contains metrics.

Source Files

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