net_instaweb::RedisCache Class Reference

#include "redis_cache.h"

Inheritance diagram for net_instaweb::RedisCache:

Public Member Functions
	RedisCache (StringPiece host, int port, ThreadSystem *thread_system, MessageHandler *message_handler, Timer *timer, int64 reconnection_delay_ms, int64 timeout_us, Statistics *stats, int database_index)
GoogleString	ServerDescription () const
void	StartUp (bool connect_now=true)
GoogleString	Name () const override
	CacheInterface implementations.
bool	IsBlocking () const override
bool	IsHealthy () const override
void	ShutDown () override
void	Get (const GoogleString &key, Callback *callback) override
	CacheInterface implementations.
void	Put (const GoogleString &key, const SharedString &value) override
void	Delete (const GoogleString &key) override
void	GetStatus (GoogleString *status_string)
int64	Redirections ()
int64	ClusterSlotsFetches ()
Public Member Functions inherited from net_instaweb::CacheInterface
virtual void	MultiGet (MultiGetRequest *request)
void	PutSwappingString (const GoogleString &key, GoogleString *value)
virtual CacheInterface *	Backend ()
virtual bool	MustEncodeKeyInValueOnPut () const
virtual void	PutWithKeyInValue (const GoogleString &key, const SharedString &key_and_value)

Static Public Member Functions
static void	InitStats (Statistics *stats)
static GoogleString	FormatName ()
static int	HashSlot (StringPiece key)
	Redis spec defined hasher for keys. Static, since it's a pure function.
Static Public Member Functions inherited from net_instaweb::CacheInterface
static const char *	KeyStateName (KeyState state)

Friends
class	RedisCacheTest

Additional Inherited Members
Public Types inherited from net_instaweb::CacheInterface
enum	KeyState {   kAvailable = 0, kNotFound = 1, kOverload = 2, kNetworkError = 3,   kTimeout = 4 }
typedef std::vector< KeyCallback >	MultiGetRequest
Protected Member Functions inherited from net_instaweb::CacheInterface
void	ValidateAndReportResult (const GoogleString &key, KeyState state, Callback *callback)
	Invokes callback->ValidateCandidate() and callback->Done() as appropriate.
void	ReportMultiGetNotFound (MultiGetRequest *request)

Detailed Description

Interface to Redis using hiredis library. This implementation is blocking and thread-safe. One should call StartUp() before making any requests and ShutDown() after finishing work. Connecting will be initiated on StartUp() call. If it fails there or is dropped after any request, the following reconnection strategy is used:

1. If an operation fails because of communication or protocol error, try reconnecting on the next Get/Put/Delete (without delay).
2. If (re-)connection attempt is unsuccessfull, try again on next Get/Put/Delete operation, but not until at least reconnection_delay_ms_ have passed from the previous attempt. That ensures that we do not try to connect to unreachable server a lot, but still allows us to reconnect quickly in case of network glitches.

See redis_cache.cc for details on different locks that the class has.

When using clustering, to be efficient we need to know what redis cluster machine to talk to for a given key. There are two steps: 1) hash the key in a redis-specific way determine the hash slot. 2) consult our cached copy of the slot-to-server mapping to see which server to send to. If we get a redirection after following that approach, our cached mapping is invalid and should be refreshed.

http://redis.io/topics/cluster-spec explains this all.

Todo:

TODO(yeputons): consider extracting a common interface with AprMemCache.

TODO(yeputons): consider making Redis-reported errors treated as failures.

TODO(yeputons): add redis AUTH command support.

Constructor & Destructor Documentation

net_instaweb::RedisCache::RedisCache	(	StringPiece	host,
		int	port,
		ThreadSystem *	thread_system,
		MessageHandler *	message_handler,
		Timer *	timer,
		int64	reconnection_delay_ms,
		int64	timeout_us,
		Statistics *	stats,
		int	database_index
	)

Uses ThreadSystem to generate several mutexes in constructor only. Does not take ownership of MessageHandler, Timer, and assumes that these pointers are valid throughout full lifetime of RedisCache.

Member Function Documentation

int64 net_instaweb::RedisCache::ClusterSlotsFetches ( )

inline

Total number of times we looked up the cluster slots mappings to avoid redirections.

void net_instaweb::RedisCache::GetStatus

(

GoogleString *

status_string

)

Appends detailed status for each server to a string. If a server fails to report a status, then for that server we append an error message instead.

bool net_instaweb::RedisCache::IsBlocking ( ) const

inlineoverridevirtual

Returns true if this cache is guaranteed to call its callbacks before returning from Get and MultiGet.

Implements net_instaweb::CacheInterface.

bool net_instaweb::RedisCache::IsHealthy ( ) const

overridevirtual

IsHealthy() is a rough estimation of whether cache is available for any operations. If it's false, caller may reasonably expect that making calls right now is useless as they will fail or have high latency. If it's true, operations should succeed, but some still may fail occasionally. The primary goal is to avoid sending commands to 'unhealthy' caches, e.g. if cache is under heavy load, we do not want to send even more requests.

Memory and file-based caches can simply return 'true'. It should be safe to call this frequently – the implementation shouldn't do much more that check a bool flag under mutex.

Implements net_instaweb::CacheInterface.

void net_instaweb::RedisCache::Put ( const GoogleString &  key, const SharedString &  value  )

overridevirtual

Puts a value into the cache. The value that is passed in is not modified, but the SharedString is passed by non-const pointer because its reference count is bumped.

Implements net_instaweb::CacheInterface.

int64 net_instaweb::RedisCache::Redirections ( )

inline

Total number of times we hit one server and were redirected to a different one.

void net_instaweb::RedisCache::ShutDown ( )

overridevirtual

Stops all cache activity. Further Put/Delete calls will be dropped, and MultiGet/Get will call the callback with kNotFound immediately. Note there is no Enable(); once the cache is stopped it is stopped forever. This function is intended for use during process shutdown.

Implements net_instaweb::CacheInterface.

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The documentation for this class was generated from the following file:

• pagespeed/system/redis_cache.h