README
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#Caching
##Overview The plugin query cache maintains a bidirectional GRPC stream connection to the cache server (hosted by the plugin manager process)
Cache data is streamed row by row, in both directions.
###Cache Set
- call
CacheCommand_SET_RESULT_STARTcommand - for each row:
- stream to FDW
- stream to cache with
CacheCommand_SET_RESULT_ITERATEcommand
- mark completion with
CacheCommand_SET_RESULT_END - fetch index bucket for this table (if it exists):
CacheCommand_GET_INDEX - update index bucket and write back
CacheCommand_SET_INDEX
###Cache Get
- fetch index bucket for this table (if it exists):
CacheCommand_GET_INDEX - if this is a cache hit (i.e. an index item satisfying columns and quals exists), call
CacheCommand_GET_RESULT - cache will stream results to us a row at a time - for each row
- stream to fdw
##Concurrency The plugin may make more than one request to the cache at a time (for example, if a query consists of multiple scans with the same connetion, i.e. multiple concurrent plugin Execution calls).
Therefore results from the cache may be interleaved, e.g. the results from 2 different cache gets may be streaming at the same time
To handle this, each cache command is made using a CallId (unique time-based identifier). When making a cache command, the query cache registers a callback which is stored in a map keyed by call id.
When the cache stream receiver processes a response from the cache, it uses the response callId to find the appropriate callback function and invokes it.
##TTL
The TTL is controlled by the client, as multiple clients might be using the same connections and each may have a different TTL.
This is achieved as follows. The cache saves data with a default TTL of 5 minutes (this is the TTL passed to the underlying cache). When fetching data, the age of the retrieved data is determined using the insertion time. If the age of the data is older than the client TTL, it is considered a cache miss
NOTE: If the client TTL is greater than the default TTL of the cache, the default TTL is increased as appropriate to ensure the data remains in the cache at lkeast as long as is needed for the client TTL
Documentation
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Overview ¶
Package query_cache is a cache used to store query results.
Each plugin process has a single QueryCache instance which stores the data for all connections
Index ¶
- Constants
- func IsCacheMiss(err error) bool
- func NewPendingIndexItem(req *CacheRequest) *pendingIndexItem
- type CacheData
- type CacheMissError
- type CacheRequest
- type CacheStats
- type IndexBucket
- type IndexItem
- type QueryCache
- func (c *QueryCache) AbortSet(ctx context.Context, callId string, err error)
- func (c *QueryCache) ClearForConnection(ctx context.Context, connectionName string)
- func (c *QueryCache) EndSet(ctx context.Context, callId string) (err error)
- func (c *QueryCache) Get(ctx context.Context, req *CacheRequest, streamRowFunc func(row *sdkproto.Row)) error
- func (c *QueryCache) IterateSet(ctx context.Context, row *sdkproto.Row, callId string) error
- func (c *QueryCache) StartSet(_ context.Context, req *CacheRequest)
Constants ¶
const ( // Key column CacheMatch values CacheMatchSubset = "subset" CacheMatchExact = "exact" )
Variables ¶
This section is empty.
Functions ¶
func IsCacheMiss ¶
func NewPendingIndexItem ¶
func NewPendingIndexItem(req *CacheRequest) *pendingIndexItem
Types ¶
type CacheData ¶
type CacheData interface {
proto.Message
*sdkproto.QueryResult | *sdkproto.IndexBucket
}
type CacheMissError ¶
type CacheMissError struct{}
func (CacheMissError) Error ¶
func (CacheMissError) Error() string
type CacheRequest ¶
type CacheStats ¶
type IndexBucket ¶
type IndexBucket struct {
Items []*IndexItem
}
IndexBucket contains index items for all cache results for a given table and qual set
func IndexBucketfromProto ¶
func IndexBucketfromProto(b *proto.IndexBucket) *IndexBucket
func (*IndexBucket) Append ¶
func (b *IndexBucket) Append(item *IndexItem) *IndexBucket
func (*IndexBucket) AsProto ¶
func (b *IndexBucket) AsProto() *proto.IndexBucket
func (*IndexBucket) Get ¶
func (b *IndexBucket) Get(req *CacheRequest, keyColumns map[string]*proto.KeyColumn) *IndexItem
Get finds an index item which satisfies all columns
type IndexItem ¶
type IndexItem struct {
Columns []string
Key string
Limit int64
Quals map[string]*proto.Quals
InsertionTime time.Time
PageCount int64
}
IndexItem stores the columns and cached index for a single cached query result note - this index item it tied to a specific table and set of quals
func NewIndexItem ¶
func NewIndexItem(req *CacheRequest) *IndexItem
func (IndexItem) SatisfiesColumns ¶
SatisfiesColumns returns whether this index item satisfies the given columns used when determining whether this IndexItem satisfies a cache reques
func (IndexItem) SatisfiesLimit ¶
SatisfiesLimit returns whether this index item satisfies the given limit used when determining whether this IndexItem satisfies a cache reques
func (IndexItem) SatisfiesQuals ¶
func (i IndexItem) SatisfiesQuals(checkQualMap map[string]*proto.Quals, keyColumns map[string]*proto.KeyColumn) bool
SatisfiesQuals does this index item satisfy the check quals all data returned by check quals is returned by index quals
i.e. check quals must be a 'subset' of index quals eg our quals [], check quals [id="1"] -> SATISFIED our quals [id="1"], check quals [id="1"] -> SATISFIED our quals [id="1"], check quals [id="1", foo=2] -> SATISFIED our quals [id="1", foo=2], check quals [id="1"] -> NOT SATISFIED
NOTE: some columns cannot use this subset logic. Generally this applies to columns which represent a filter which is executed server side to filter the data returned. In this case, we only identify a cache hit if the cached data has the _same_ value for the given colummn
NOTE: if the IndexItem has a limit, the quals must be IDENTICAL (ignoring ordering)
func (IndexItem) SatisfiesTtl ¶
SatisfiesTtl does this index item satisfy the ttl requirement
type QueryCache ¶
type QueryCache struct {
Stats *CacheStats
// map of connection name to plugin schema
PluginSchemaMap map[string]*grpc.PluginSchema
// contains filtered or unexported fields
}
func NewQueryCache ¶
func NewQueryCache(pluginName string, pluginSchemaMap map[string]*grpc.PluginSchema, maxCacheStorageMb int) (*QueryCache, error)
func (*QueryCache) AbortSet ¶
func (c *QueryCache) AbortSet(ctx context.Context, callId string, err error)
func (*QueryCache) ClearForConnection ¶
func (c *QueryCache) ClearForConnection(ctx context.Context, connectionName string)
ClearForConnection removes all cache entries for the given connection
func (*QueryCache) EndSet ¶
func (c *QueryCache) EndSet(ctx context.Context, callId string) (err error)
func (*QueryCache) Get ¶
func (c *QueryCache) Get(ctx context.Context, req *CacheRequest, streamRowFunc func(row *sdkproto.Row)) error
func (*QueryCache) IterateSet ¶
func (*QueryCache) StartSet ¶
func (c *QueryCache) StartSet(_ context.Context, req *CacheRequest)
Source Files