Data Structures¶

class OpenDir

An open directory entry. It contains all the information of a Dir plus additional information from the first Doc.

class CacheVC

A virtual connection class which accepts input for writing to cache.

int CacheVC::openReadStartHead(int event, Event *e)

Performs the initial read for a cached object.

int CacheVC::openReadStartEarliest(int event, Event *e)

Performs the initial read for an alternate of an object.

class HttpTunnel

Data transfer driver. This contains a set of producers. Each producer is connected to one or more consumers. The tunnel handles events and buffers so that data moves from producers to consumers. The data, as much as possible, is kept in reference counted buffers so that copies are done only when the data is modified or for sources (which acquire data from outside Traffic Server) and sinks (which move data to outside Traffic Server).

class CacheControlResult

Holds the data from a line in cache.config.

class CacheHTTPInfoVector

Defined in P_CacheHttp.h. This is an array of HTTPInfo objects and serves as the respository of information about alternates of an object. It is marshaled as part of the metadata for an object in the cache.

class HTTPInfo

Defined in HTTP.h.

This class is a wrapper for HTTPCacheAlt. It provides the external API for accessing data in the wrapped class. It contains only a pointer (possibly NULL) to an instance of the wrapped class.

class CacheHTTPInfo

A typedef for HTTPInfo.

class HTTPCacheAlt

Defined in HTTP.h.

This is the metadata for a single alternate for a cached object. It contains, among other data, the following:

• The key for the earliest Doc of the alternate.
• The request and response headers.
• The fragment offset table.[#fragment-offset-table]_
• Timestamps for request and response from origin server.
class EvacuationBlock

Record for evacuation.

class Vol

This represents a storage unit inside a cache volume.

off_t data_blocks

The number of blocks of storage in the stripe.

off_t segments

The number of segments in the volume. This will be roughly the total number of entries divided by the number of entries in a segment. It will be rounded up to cover all entries.

off_t buckets

The number of buckets in the volume. This will be roughly the number of entries in a segment divided by DIR_DEPTH. For currently defined values this is around 16,384 (2^16 / 4). Buckets are used as the targets of the index hash.

DLL<EvacuationBlock> evacuate

Array of of EvacuationBlock buckets. This is sized so there is one bucket for every evacuation span.

off_t len

Length of stripe in bytes.

int Vol::evac_range(off_t low, off_t high, int evac_phase)

Start an evacuation if there is any EvacuationBlock in the range from low to high. Return 0 if no evacuation was started, non-zero otherwise.

class CacheVol

A cache volume as described in volume.config.

class Doc

Defined in P_CacheVol.h.

uint32_t magic

Validity check value. Set to DOC_MAGIC for a valid document.

uint32_t len

The length of this segment including the header length, fragment table, and this structure.

uint64_t total_len

Total length of the entire document not including meta data but including headers.

INK_MD5 first_key

First index key in the document (the index key used to locate this object in the volume index).

INK_MD5 key

The index key for this fragment. Fragment keys are computationally chained so that the key for the next and previous fragments can be computed from this key.

uint32_t hlen

uint8_t ftype

Fragment type. Currently only CACHE_FRAG_TYPE_HTTP is used. Other types may be used for cache extensions if those are ever implemented.

uint24_t flen

Fragment table length, if any. Only the first Doc in an object should contain a fragment table.

The fragment table is a list of offsets relative to the HTTP content (not counting metadata or HTTP headers). Each offset is the byte offset of the first byte in the fragment. The first element in the table is the second fragment (what would be index 1 for an array). The offset for the first fragment is of course always zero and so not stored. The purpose of this is to enable a fast seek for range requests. Given the first Doc the fragment containing the first byte in the range can be computed and loaded directly without further disk access.

Removed as of version 3.3.0. [1]

uint32_t sync_serial

Unknown.

uint32_t write_serial

Unknown.

uint32_t pinned

Flag and timer for pinned objects.

uint32_t checksum

Unknown.

class VolHeaderFooter

Footnotes

 [1] Changed in version 3.2.0. This previously resided in the first Doc but that caused different alternates to share the same fragment table.