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Reference Guide
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TTreeCache Class Reference

A specialized TFileCacheRead object for a TTree.

This class acts as a file cache, registering automatically the baskets from the branches being processed (TTree::Draw or TTree::Process and TSelectors) when in the learning phase. The learning phase is by default 100 entries. It can be changed via TTreeCache::SetLearnEntries.

This cache speeds-up considerably the performance, in particular when the Tree is accessed remotely via a high latency network.

The default cache size (10 Mbytes) may be changed via the function TTree::SetCacheSize

Only the baskets for the requested entry range are put in the cache

For each Tree being processed a TTreeCache object is created. This object is automatically deleted when the Tree is deleted or when the file is deleted.

The learning period is started or restarted when:

The learning period is stopped (and prefetching is actually started) when:

WHY DO WE NEED the TreeCache when doing data analysis?

When writing a TTree, the branch buffers are kept in memory. A typical branch buffersize (before compression) is typically 32 KBytes. After compression, the zipped buffer may be just a few Kbytes. The branch buffers cannot be much larger in case of Trees with several hundred or thousand branches.

When writing, this does not generate a performance problem because branch buffers are always written sequentially and the OS is in general clever enough to flush the data to the output file when a few MBytes of data have to be written. When reading at the contrary, one may hit a performance problem when reading across a network (LAN or WAN) and the network latency is high. For example in a WAN with 10ms latency, reading 1000 buffers of 10 KBytes each with no cache will imply 10s penalty where a local read of the 10 MBytes would take about 1 second.

The TreeCache will try to prefetch all the buffers for the selected branches such that instead of transferring 1000 buffers of 10 Kbytes, it will be able to transfer one single large buffer of 10 Mbytes in one single transaction. Not only the TreeCache minimizes the number of transfers, but in addition it can sort the blocks to be read in increasing order such that the file is read sequentially.

Systems like xrootd, dCache or httpd take advantage of the TreeCache in reading ahead as much data as they can and return to the application the maximum data specified in the cache and have the next chunk of data ready when the next request comes.

HOW TO USE the TreeCache

A few use cases are discussed below. A cache may be created with automatic sizing when a TTree is used:

Caches are created and automatically sized for TTrees when TTreeCache.Size or the environment variable ROOT_TTREECACHE_SIZE is set to a sizing factor.

But there are many possible configurations where manual control may be wanted. In some applications you know a priori the list of branches to read. In other applications the analysis loop calls several layers of user functions where it is impossible to predict a priori which branches will be used. This is probably the most frequent case. In this case ROOT I/O will flag used branches automatically when a branch buffer is read during the learning phase. The TreeCache interface provides functions to instruct the cache about the used branches if they are known a priori. In the examples below, portions of analysis code are shown. The few statements involving the TreeCache are marked with //<<<

1. with TTree::Draw

the TreeCache is automatically used by TTree::Draw. The function knows which branches are used in the query and it puts automatically these branches in the cache. The entry range is also known automatically.

2. with TTree::Process and TSelectors

You must enable the cache and tell the system which branches to cache and also specify the entry range. It is important to specify the entry range in case you process only a subset of the events, otherwise you run the risk to store in the cache entries that you do not need.

#### example 2a

TTree *T = (TTree*)f->Get("mytree");
Long64_t nentries = T->GetEntries();
Int_t cachesize = 10000000; //10 MBytes
T->SetCacheSize(cachesize); //<<<
T->AddBranchToCache("*",kTRUE); //<<< add all branches to the cache
T->Process('myselector.C+");
//in the TSelector::Process function we read all branches
T->GetEntry(i);
... here you process your entry

example 2b

in the Process function we read a subset of the branches. Only the branches used in the first entry will be put in the cache

TTree *T = (TTree*)f->Get("mytree");
//we want to process only the 200 first entries
Long64_t nentries=200;
int efirst= 0;
int elast = efirst+nentries;
Int_t cachesize = 10000000; //10 MBytes
TTreeCache::SetLearnEntries(1); //<<< we can take the decision after 1 entry
T->SetCacheSize(cachesize); //<<<
T->SetCacheEntryRange(efirst,elast); //<<<
T->Process('myselector.C+","",nentries,efirst);
// in the TSelector::Process we read only 2 branches
TBranch *b1 = T->GetBranch("branch1");
b1->GetEntry(i);
if (somecondition) return;
TBranch *b2 = T->GetBranch("branch2");
b2->GetEntry(i);
... here you process your entry

3. with your own event loop

example 3a

in your analysis loop, you always use 2 branches. You want to prefetch the branch buffers for these 2 branches only.

TTree *T = (TTree*)f->Get("mytree");
TBranch *b1 = T->GetBranch("branch1");
TBranch *b2 = T->GetBranch("branch2");
Long64_t nentries = T->GetEntries();
Int_t cachesize = 10000000; //10 MBytes
T->SetCacheSize(cachesize); //<<<
T->AddBranchToCache(b1,kTRUE); //<<<add branch1 and branch2 to the cache
T->AddBranchToCache(b2,kTRUE); //<<<
for (Long64_t i=0;i<nentries;i++) {
T->LoadTree(i); //<<< important call when calling TBranch::GetEntry after
b1->GetEntry(i);
if (some condition not met) continue;
b2->GetEntry(i);
if (some condition not met) continue;
//here we read the full event only in some rare cases.
//there is no point in caching the other branches as it might be
//more economical to read only the branch buffers really used.
T->GetEntry(i);
.. process the rare but interesting cases.
... here you process your entry
}

example 3b

in your analysis loop, you always use 2 branches in the main loop. you also call some analysis functions where a few more branches will be read. but you do not know a priori which ones. There is no point in prefetching branches that will be used very rarely.

TTree *T = (TTree*)f->Get("mytree");
Long64_t nentries = T->GetEntries();
Int_t cachesize = 10000000; //10 MBytes
T->SetCacheSize(cachesize); //<<<
T->SetCacheLearnEntries(5); //<<< we can take the decision after 5 entries
TBranch *b1 = T->GetBranch("branch1");
TBranch *b2 = T->GetBranch("branch2");
for (Long64_t i=0;i<nentries;i++) {
T->LoadTree(i);
b1->GetEntry(i);
if (some condition not met) continue;
b2->GetEntry(i);
//at this point we may call a user function where a few more branches
//will be read conditionally. These branches will be put in the cache
//if they have been used in the first 10 entries
if (some condition not met) continue;
//here we read the full event only in some rare cases.
//there is no point in caching the other branches as it might be
//more economical to read only the branch buffers really used.
T->GetEntry(i);
.. process the rare but interesting cases.
... here you process your entry
}

SPECIAL CASES WHERE TreeCache should not be activated

When reading only a small fraction of all entries such that not all branch buffers are read, it might be faster to run without a cache.

HOW TO VERIFY That the TreeCache has been used and check its performance

Once your analysis loop has terminated, you can access/print the number of effective system reads for a given file with a code like (where TFile* f is a pointer to your file)

printf("Reading %lld bytes in %d transactions\n",f->GetBytesRead(), f->GetReadCalls());

Definition at line 30 of file TTreeCache.h.

Public Types

enum  EPrefillType { kNoPrefill, kAllBranches }
 
- Public Types inherited from TObject
enum  {
  kIsOnHeap = 0x01000000, kNotDeleted = 0x02000000, kZombie = 0x04000000, kInconsistent = 0x08000000,
  kBitMask = 0x00ffffff
}
 
enum  { kSingleKey = BIT(0), kOverwrite = BIT(1), kWriteDelete = BIT(2) }
 
enum  EDeprecatedStatusBits { kObjInCanvas = BIT(3) }
 
enum  EStatusBits {
  kCanDelete = BIT(0), kMustCleanup = BIT(3), kIsReferenced = BIT(4), kHasUUID = BIT(5),
  kCannotPick = BIT(6), kNoContextMenu = BIT(8), kInvalidObject = BIT(13)
}
 

Public Member Functions

 TTreeCache ()
 Default Constructor. More...
 
 TTreeCache (TTree *tree, Int_t buffersize=0)
 Constructor. More...
 
virtual ~TTreeCache ()
 Destructor. (in general called by the TFile destructor) More...
 
virtual Int_t AddBranch (TBranch *b, Bool_t subgbranches=kFALSE)
 Add a branch to the list of branches to be stored in the cache this function is called by TBranch::GetBasket Returns: More...
 
virtual Int_t AddBranch (const char *branch, Bool_t subbranches=kFALSE)
 Add a branch to the list of branches to be stored in the cache this is to be used by user (thats why we pass the name of the branch). More...
 
virtual void Disable ()
 
virtual Int_t DropBranch (TBranch *b, Bool_t subbranches=kFALSE)
 Remove a branch to the list of branches to be stored in the cache this function is called by TBranch::GetBasket. More...
 
virtual Int_t DropBranch (const char *branch, Bool_t subbranches=kFALSE)
 Remove a branch to the list of branches to be stored in the cache this is to be used by user (thats why we pass the name of the branch). More...
 
virtual void Enable ()
 
virtual Bool_t FillBuffer ()
 Fill the cache buffer with the branches in the cache. More...
 
const TObjArrayGetCachedBranches () const
 
EPrefillType GetConfiguredPrefillType () const
 Return the desired prefill type from the environment or resource variable. More...
 
Double_t GetEfficiency () const
 Give the total efficiency of the cache... More...
 
Double_t GetEfficiencyRel () const
 This will indicate a sort of relative efficiency... More...
 
virtual Int_t GetEntryMax () const
 
virtual Int_t GetEntryMin () const
 
virtual EPrefillType GetLearnPrefill () const
 
TTreeGetTree () const
 
Bool_t IsAutoCreated () const
 
virtual Bool_t IsEnabled () const
 
virtual Bool_t IsLearning () const
 
virtual void LearnPrefill ()
 Perform an initial prefetch, attempting to read as much of the learning phase baskets for all branches at once. More...
 
virtual void Print (Option_t *option="") const
 Print cache statistics. More...
 
virtual Int_t ReadBuffer (char *buf, Long64_t pos, Int_t len)
 Read buffer at position pos if the request is in the list of prefetched blocks read from fBuffer. More...
 
virtual Int_t ReadBufferNormal (char *buf, Long64_t pos, Int_t len)
 Old method ReadBuffer before the addition of the prefetch mechanism. More...
 
virtual Int_t ReadBufferPrefetch (char *buf, Long64_t pos, Int_t len)
 Used to read a chunk from a block previously fetched. More...
 
virtual void ResetCache ()
 This will simply clear the cache. More...
 
void SetAutoCreated (Bool_t val)
 
virtual Int_t SetBufferSize (Int_t buffersize)
 Change the underlying buffer size of the cache. More...
 
virtual void SetEntryRange (Long64_t emin, Long64_t emax)
 Set the minimum and maximum entry number to be processed this information helps to optimize the number of baskets to read when prefetching the branch buffers. More...
 
virtual void SetFile (TFile *file, TFile::ECacheAction action=TFile::kDisconnect)
 Overload to make sure that the object specific. More...
 
virtual void SetLearnPrefill (EPrefillType type=kNoPrefill)
 Set whether the learning period is started with a prefilling of the cache and which type of prefilling is used. More...
 
void StartLearningPhase ()
 The name should be enough to explain the method. More...
 
virtual void StopLearningPhase ()
 This is the counterpart of StartLearningPhase() and can be used to stop the learning phase. More...
 
virtual void UpdateBranches (TTree *tree)
 Update pointer to current Tree and recompute pointers to the branches in the cache. More...
 
- Public Member Functions inherited from TFileCacheRead
 TFileCacheRead ()
 Default Constructor. More...
 
 TFileCacheRead (TFile *file, Int_t buffersize, TObject *tree=0)
 Creates a TFileCacheRead data structure. More...
 
virtual ~TFileCacheRead ()
 Destructor. More...
 
virtual void AddNoCacheBytesRead (Long64_t len)
 
virtual void AddNoCacheReadCalls (Int_t reads)
 
virtual void Close (Option_t *option="")
 Close out any threads or asynchronous fetches used by the underlying implementation. More...
 
virtual Int_t GetBufferSize () const
 
virtual Long64_t GetBytesRead () const
 
virtual Long64_t GetBytesReadExtra () const
 
TFileGetFile () const
 
virtual Long64_t GetNoCacheBytesRead () const
 
virtual Int_t GetNoCacheReadCalls () const
 
Int_t GetNseek () const
 
Int_t GetNtot () const
 
Long64_t GetPrefetchedBlocks () const
 
virtual TFilePrefetchGetPrefetchObj ()
 
virtual Int_t GetReadCalls () const
 
virtual Int_t GetUnzipBuffer (char **, Long64_t, Int_t, Bool_t *)
 
virtual Bool_t IsAsyncReading () const
 
virtual Bool_t IsEnablePrefetching () const
 
virtual void Prefetch (Long64_t pos, Int_t len)
 Add block of length len at position pos in the list of blocks to be prefetched. More...
 
virtual Int_t ReadBufferExt (char *buf, Long64_t pos, Int_t len, Int_t &loc)
 
virtual Int_t ReadBufferExtNormal (char *buf, Long64_t pos, Int_t len, Int_t &loc)
 Base function for ReadBuffer. More...
 
virtual Int_t ReadBufferExtPrefetch (char *buf, Long64_t pos, Int_t len, Int_t &loc)
 prefetch the first block More...
 
virtual void SecondPrefetch (Long64_t, Int_t)
 
virtual void SecondSort ()
 Sort buffers to be prefetched in increasing order of positions. More...
 
virtual void SetEnablePrefetching (Bool_t setPrefetching=kFALSE)
 Set the prefetching mode of this file. More...
 
virtual void SetSkipZip (Bool_t=kTRUE)
 
virtual void Sort ()
 Sort buffers to be prefetched in increasing order of positions. More...
 
virtual void WaitFinishPrefetch ()
 
- Public Member Functions inherited from TObject
 TObject ()
 TObject constructor. More...
 
 TObject (const TObject &object)
 TObject copy ctor. More...
 
virtual ~TObject ()
 TObject destructor. More...
 
void AbstractMethod (const char *method) const
 Use this method to implement an "abstract" method that you don't want to leave purely abstract. More...
 
virtual void AppendPad (Option_t *option="")
 Append graphics object to current pad. More...
 
virtual void Browse (TBrowser *b)
 Browse object. May be overridden for another default action. More...
 
ULong_t CheckedHash ()
 Checked and record whether for this class has a consistent Hash/RecursiveRemove setup (*) and then return the regular Hash value for this object. More...
 
virtual const char * ClassName () const
 Returns name of class to which the object belongs. More...
 
virtual void Clear (Option_t *="")
 
virtual TObjectClone (const char *newname="") const
 Make a clone of an object using the Streamer facility. More...
 
virtual Int_t Compare (const TObject *obj) const
 Compare abstract method. More...
 
virtual void Copy (TObject &object) const
 Copy this to obj. More...
 
virtual void Delete (Option_t *option="")
 Delete this object. More...
 
virtual Int_t DistancetoPrimitive (Int_t px, Int_t py)
 Computes distance from point (px,py) to the object. More...
 
virtual void Draw (Option_t *option="")
 Default Draw method for all objects. More...
 
virtual void DrawClass () const
 Draw class inheritance tree of the class to which this object belongs. More...
 
virtual TObjectDrawClone (Option_t *option="") const
 Draw a clone of this object in the current selected pad for instance with: gROOT->SetSelectedPad(gPad). More...
 
virtual void Dump () const
 Dump contents of object on stdout. More...
 
virtual void Error (const char *method, const char *msgfmt,...) const
 Issue error message. More...
 
virtual void Execute (const char *method, const char *params, Int_t *error=0)
 Execute method on this object with the given parameter string, e.g. More...
 
virtual void Execute (TMethod *method, TObjArray *params, Int_t *error=0)
 Execute method on this object with parameters stored in the TObjArray. More...
 
virtual void ExecuteEvent (Int_t event, Int_t px, Int_t py)
 Execute action corresponding to an event at (px,py). More...
 
virtual void Fatal (const char *method, const char *msgfmt,...) const
 Issue fatal error message. More...
 
virtual TObjectFindObject (const char *name) const
 Must be redefined in derived classes. More...
 
virtual TObjectFindObject (const TObject *obj) const
 Must be redefined in derived classes. More...
 
virtual Option_tGetDrawOption () const
 Get option used by the graphics system to draw this object. More...
 
virtual const char * GetIconName () const
 Returns mime type name of object. More...
 
virtual const char * GetName () const
 Returns name of object. More...
 
virtual char * GetObjectInfo (Int_t px, Int_t py) const
 Returns string containing info about the object at position (px,py). More...
 
virtual Option_tGetOption () const
 
virtual const char * GetTitle () const
 Returns title of object. More...
 
virtual UInt_t GetUniqueID () const
 Return the unique object id. More...
 
virtual Bool_t HandleTimer (TTimer *timer)
 Execute action in response of a timer timing out. More...
 
virtual ULong_t Hash () const
 Return hash value for this object. More...
 
Bool_t HasInconsistentHash () const
 Return true is the type of this object is known to have an inconsistent setup for Hash and RecursiveRemove (i.e. More...
 
virtual void Info (const char *method, const char *msgfmt,...) const
 Issue info message. More...
 
virtual Bool_t InheritsFrom (const char *classname) const
 Returns kTRUE if object inherits from class "classname". More...
 
virtual Bool_t InheritsFrom (const TClass *cl) const
 Returns kTRUE if object inherits from TClass cl. More...
 
virtual void Inspect () const
 Dump contents of this object in a graphics canvas. More...
 
void InvertBit (UInt_t f)
 
virtual Bool_t IsEqual (const TObject *obj) const
 Default equal comparison (objects are equal if they have the same address in memory). More...
 
virtual Bool_t IsFolder () const
 Returns kTRUE in case object contains browsable objects (like containers or lists of other objects). More...
 
R__ALWAYS_INLINE Bool_t IsOnHeap () const
 
virtual Bool_t IsSortable () const
 
R__ALWAYS_INLINE Bool_t IsZombie () const
 
virtual void ls (Option_t *option="") const
 The ls function lists the contents of a class on stdout. More...
 
void MayNotUse (const char *method) const
 Use this method to signal that a method (defined in a base class) may not be called in a derived class (in principle against good design since a child class should not provide less functionality than its parent, however, sometimes it is necessary). More...
 
virtual Bool_t Notify ()
 This method must be overridden to handle object notification. More...
 
void Obsolete (const char *method, const char *asOfVers, const char *removedFromVers) const
 Use this method to declare a method obsolete. More...
 
void operator delete (void *ptr)
 Operator delete. More...
 
void operator delete[] (void *ptr)
 Operator delete []. More...
 
voidoperator new (size_t sz)
 
voidoperator new (size_t sz, void *vp)
 
voidoperator new[] (size_t sz)
 
voidoperator new[] (size_t sz, void *vp)
 
TObjectoperator= (const TObject &rhs)
 TObject assignment operator. More...
 
virtual void Paint (Option_t *option="")
 This method must be overridden if a class wants to paint itself. More...
 
virtual void Pop ()
 Pop on object drawn in a pad to the top of the display list. More...
 
virtual Int_t Read (const char *name)
 Read contents of object with specified name from the current directory. More...
 
virtual void RecursiveRemove (TObject *obj)
 Recursively remove this object from a list. More...
 
void ResetBit (UInt_t f)
 
virtual void SaveAs (const char *filename="", Option_t *option="") const
 Save this object in the file specified by filename. More...
 
virtual void SavePrimitive (std::ostream &out, Option_t *option="")
 Save a primitive as a C++ statement(s) on output stream "out". More...
 
void SetBit (UInt_t f, Bool_t set)
 Set or unset the user status bits as specified in f. More...
 
void SetBit (UInt_t f)
 
virtual void SetDrawOption (Option_t *option="")
 Set drawing option for object. More...
 
virtual void SetUniqueID (UInt_t uid)
 Set the unique object id. More...
 
virtual void SysError (const char *method, const char *msgfmt,...) const
 Issue system error message. More...
 
R__ALWAYS_INLINE Bool_t TestBit (UInt_t f) const
 
Int_t TestBits (UInt_t f) const
 
virtual void UseCurrentStyle ()
 Set current style settings in this object This function is called when either TCanvas::UseCurrentStyle or TROOT::ForceStyle have been invoked. More...
 
virtual void Warning (const char *method, const char *msgfmt,...) const
 Issue warning message. More...
 
virtual Int_t Write (const char *name=0, Int_t option=0, Int_t bufsize=0)
 Write this object to the current directory. More...
 
virtual Int_t Write (const char *name=0, Int_t option=0, Int_t bufsize=0) const
 Write this object to the current directory. More...
 

Static Public Member Functions

static Int_t GetLearnEntries ()
 Static function returning the number of entries used to train the cache see SetLearnEntries. More...
 
static void SetLearnEntries (Int_t n=10)
 Static function to set the number of entries to be used in learning mode The default value for n is 10. More...
 
- Static Public Member Functions inherited from TObject
static Long_t GetDtorOnly ()
 Return destructor only flag. More...
 
static Bool_t GetObjectStat ()
 Get status of object stat flag. More...
 
static void SetDtorOnly (void *obj)
 Set destructor only flag. More...
 
static void SetObjectStat (Bool_t stat)
 Turn on/off tracking of objects in the TObjectTable. More...
 

Protected Attributes

Bool_t fAutoCreated
 ! true if cache was automatically created More...
 
TObjArrayfBranches
 ! List of branches to be stored in the cache More...
 
TListfBrNames
 ! list of branch names in the cache More...
 
Bool_t fEnabled
 ! cache enabled for cached reading More...
 
Long64_t fEntryCurrent
 ! current lowest entry number in the cache More...
 
Long64_t fEntryMax
 ! last entry in the cache More...
 
Long64_t fEntryMin
 ! first entry in the cache More...
 
Long64_t fEntryNext
 ! next entry number where cache must be filled More...
 
Int_t fFillTimes
 ! how many times we can fill the current buffer More...
 
Bool_t fFirstBuffer
 ! true if first buffer is used for prefetching More...
 
Long64_t fFirstEntry
 ! save the value of the first entry More...
 
Bool_t fFirstTime
 ! save the fact that we processes the first entry More...
 
Bool_t fIsLearning
 ! true if cache is in learning mode More...
 
Bool_t fIsManual
 ! true if cache is StopLearningPhase was used More...
 
Int_t fNbranches
 ! Number of branches in the cache More...
 
Int_t fNReadMiss
 Number of blocks read and not found in the cache. More...
 
Int_t fNReadOk
 Number of blocks read and found in the cache. More...
 
Int_t fNReadPref
 Number of blocks that were prefetched. More...
 
Bool_t fOneTime
 ! used in the learning phase More...
 
EPrefillType fPrefillType
 Whether a pre-filling is enabled (and if applicable which type) More...
 
Bool_t fReadDirectionSet
 ! read direction established More...
 
Bool_t fReverseRead
 ! reading in reverse mode More...
 
TTreefTree
 ! pointer to the current Tree More...
 
- Protected Attributes inherited from TFileCacheRead
Bool_t fAsyncReading
 
Bool_t fBIsSorted
 
Bool_t fBIsTransferred
 
Int_tfBLen
 [fBNb] More...
 
Int_t fBNb
 
Int_t fBNseek
 
Int_t fBNtot
 
Long64_tfBPos
 [fBNb] More...
 
Long64_tfBSeek
 [fBNseek] More...
 
Int_tfBSeekIndex
 [fBNseek] More...
 
Int_tfBSeekLen
 [fBNseek] More...
 
Int_tfBSeekPos
 [fBNseek] More...
 
Int_t fBSeekSize
 
Long64_tfBSeekSort
 [fBNseek] More...
 
Int_tfBSeekSortLen
 [fBNseek] More...
 
char * fBuffer
 [fBufferSize] buffer of contiguous prefetched blocks More...
 
Int_t fBufferLen
 Current buffer length (<= fBufferSize) More...
 
Int_t fBufferSize
 Allocated size of fBuffer (at a given time) More...
 
Int_t fBufferSizeMin
 Original size of fBuffer. More...
 
Long64_t fBytesRead
 Number of bytes read for this cache. More...
 
Long64_t fBytesReadExtra
 Number of extra bytes (overhead) read by the readahead buffer. More...
 
Bool_t fEnablePrefetching
 reading by prefetching asynchronously More...
 
TFilefFile
 Pointer to file. More...
 
Bool_t fIsSorted
 True if fSeek array is sorted. More...
 
Bool_t fIsTransferred
 True when fBuffer contains something valid. More...
 
Int_tfLen
 [fNb] Length of long buffers More...
 
Int_t fNb
 Number of long buffers. More...
 
Long64_t fNoCacheBytesRead
 Number of bytes read by basket to fill cached tree. More...
 
Int_t fNoCacheReadCalls
 Number of read calls by basket to fill cached tree. More...
 
Int_t fNseek
 Number of blocks to be prefetched. More...
 
Int_t fNtot
 Total size of prefetched blocks. More...
 
Long64_tfPos
 [fNb] start of long buffers More...
 
TFilePrefetchfPrefetch
 ! Object that does the asynchronous reading in another thread More...
 
Long64_t fPrefetchedBlocks
 Number of blocks prefetched. More...
 
Int_t fReadCalls
 Number of read calls for this cache. More...
 
Long64_tfSeek
 [fNseek] Position on file of buffers to be prefetched More...
 
Int_tfSeekIndex
 [fNseek] sorted index table of fSeek More...
 
Int_tfSeekLen
 [fNseek] Length of buffers to be prefetched More...
 
Int_tfSeekPos
 [fNseek] Position of sorted blocks in fBuffer More...
 
Int_t fSeekSize
 Allocated size of fSeek. More...
 
Long64_tfSeekSort
 [fNseek] Position on file of buffers to be prefetched (sorted) More...
 
Int_tfSeekSortLen
 [fNseek] Length of buffers to be prefetched (sorted) More...
 

Static Protected Attributes

static Int_t fgLearnEntries = 100
 number of entries used for learning mode More...
 

Private Member Functions

 TTreeCache (const TTreeCache &)
 
TTreeCacheoperator= (const TTreeCache &)
 

Additional Inherited Members

- Protected Member Functions inherited from TFileCacheRead
void SetEnablePrefetchingImpl (Bool_t setPrefetching=kFALSE)
 TFileCacheRead implementation of SetEnablePrefetching. More...
 
- Protected Member Functions inherited from TObject
virtual void DoError (int level, const char *location, const char *fmt, va_list va) const
 Interface to ErrorHandler (protected). More...
 
void MakeZombie ()
 

#include <TTreeCache.h>

Inheritance diagram for TTreeCache:
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Member Enumeration Documentation

◆ EPrefillType

Enumerator
kNoPrefill 
kAllBranches 

Definition at line 33 of file TTreeCache.h.

Constructor & Destructor Documentation

◆ TTreeCache() [1/3]

TTreeCache::TTreeCache ( const TTreeCache )
private

◆ TTreeCache() [2/3]

TTreeCache::TTreeCache ( )

Default Constructor.

Definition at line 252 of file TTreeCache.cxx.

◆ TTreeCache() [3/3]

TTreeCache::TTreeCache ( TTree tree,
Int_t  buffersize = 0 
)

Constructor.

Definition at line 282 of file TTreeCache.cxx.

◆ ~TTreeCache()

TTreeCache::~TTreeCache ( )
virtual

Destructor. (in general called by the TFile destructor)

Definition at line 315 of file TTreeCache.cxx.

Member Function Documentation

◆ AddBranch() [1/2]

Int_t TTreeCache::AddBranch ( TBranch b,
Bool_t  subbranches = kFALSE 
)
virtual

Add a branch to the list of branches to be stored in the cache this function is called by TBranch::GetBasket Returns:

  • 0 branch added or already included
  • -1 on error

Reimplemented from TFileCacheRead.

Reimplemented in TTreeCacheUnzip.

Definition at line 332 of file TTreeCache.cxx.

◆ AddBranch() [2/2]

Int_t TTreeCache::AddBranch ( const char *  bname,
Bool_t  subbranches = kFALSE 
)
virtual

Add a branch to the list of branches to be stored in the cache this is to be used by user (thats why we pass the name of the branch).

It works in exactly the same way as TTree::SetBranchStatus so you probably want to look over there for details about the use of bname with regular expressions. The branches are taken with respect to the Owner of this TTreeCache (i.e. the original Tree) NB: if bname="*" all branches are put in the cache and the learning phase stopped Returns:

  • 0 branch added or already included
  • -1 on error

Reimplemented from TFileCacheRead.

Reimplemented in TTreeCacheUnzip.

Definition at line 389 of file TTreeCache.cxx.

◆ Disable()

virtual void TTreeCache::Disable ( )
inlinevirtual

Definition at line 74 of file TTreeCache.h.

◆ DropBranch() [1/2]

Int_t TTreeCache::DropBranch ( TBranch b,
Bool_t  subbranches = kFALSE 
)
virtual

Remove a branch to the list of branches to be stored in the cache this function is called by TBranch::GetBasket.

Returns:

  • 0 branch dropped or not in cache
  • -1 on error

Definition at line 484 of file TTreeCache.cxx.

◆ DropBranch() [2/2]

Int_t TTreeCache::DropBranch ( const char *  bname,
Bool_t  subbranches = kFALSE 
)
virtual

Remove a branch to the list of branches to be stored in the cache this is to be used by user (thats why we pass the name of the branch).

It works in exactly the same way as TTree::SetBranchStatus so you probably want to look over there for details about the use of bname with regular expressions. The branches are taken with respect to the Owner of this TTreeCache (i.e. the original Tree) NB: if bname="*" all branches are put in the cache and the learning phase stopped Returns:

  • 0 branch dropped or not in cache
  • -1 on error

Definition at line 529 of file TTreeCache.cxx.

◆ Enable()

virtual void TTreeCache::Enable ( )
inlinevirtual

Definition at line 75 of file TTreeCache.h.

◆ FillBuffer()

Bool_t TTreeCache::FillBuffer ( )
virtual

Fill the cache buffer with the branches in the cache.

Reimplemented in TTreeCacheUnzip.

Definition at line 619 of file TTreeCache.cxx.

◆ GetCachedBranches()

const TObjArray* TTreeCache::GetCachedBranches ( ) const
inline

Definition at line 76 of file TTreeCache.h.

◆ GetConfiguredPrefillType()

TTreeCache::EPrefillType TTreeCache::GetConfiguredPrefillType ( ) const

Return the desired prefill type from the environment or resource variable.

  • 0 - No prefill
  • 1 - All branches

Definition at line 924 of file TTreeCache.cxx.

◆ GetEfficiency()

Double_t TTreeCache::GetEfficiency ( ) const

Give the total efficiency of the cache...

defined as the ratio of blocks found in the cache vs. the number of blocks prefetched ( it could be more than 1 if we read the same block from the cache more than once )

Note: This should eb used at the end of the processing or we will get incomplete stats

Definition at line 947 of file TTreeCache.cxx.

◆ GetEfficiencyRel()

Double_t TTreeCache::GetEfficiencyRel ( ) const

This will indicate a sort of relative efficiency...

a ratio of the reads found in the cache to the number of reads so far

Definition at line 959 of file TTreeCache.cxx.

◆ GetEntryMax()

virtual Int_t TTreeCache::GetEntryMax ( ) const
inlinevirtual

Definition at line 81 of file TTreeCache.h.

◆ GetEntryMin()

virtual Int_t TTreeCache::GetEntryMin ( ) const
inlinevirtual

Definition at line 80 of file TTreeCache.h.

◆ GetLearnEntries()

Int_t TTreeCache::GetLearnEntries ( )
static

Static function returning the number of entries used to train the cache see SetLearnEntries.

Definition at line 971 of file TTreeCache.cxx.

◆ GetLearnPrefill()

virtual EPrefillType TTreeCache::GetLearnPrefill ( ) const
inlinevirtual

Definition at line 83 of file TTreeCache.h.

◆ GetTree()

TTree* TTreeCache::GetTree ( ) const
inline

Definition at line 84 of file TTreeCache.h.

◆ IsAutoCreated()

Bool_t TTreeCache::IsAutoCreated ( ) const
inline

Definition at line 85 of file TTreeCache.h.

◆ IsEnabled()

virtual Bool_t TTreeCache::IsEnabled ( ) const
inlinevirtual

Definition at line 86 of file TTreeCache.h.

◆ IsLearning()

virtual Bool_t TTreeCache::IsLearning ( ) const
inlinevirtual

Reimplemented from TFileCacheRead.

Definition at line 87 of file TTreeCache.h.

◆ LearnPrefill()

void TTreeCache::LearnPrefill ( )
virtual

Perform an initial prefetch, attempting to read as much of the learning phase baskets for all branches at once.

Definition at line 1293 of file TTreeCache.cxx.

◆ operator=()

TTreeCache& TTreeCache::operator= ( const TTreeCache )
private

◆ Print()

void TTreeCache::Print ( Option_t option = "") const
virtual

Print cache statistics.

Like:

******TreeCache statistics for file: cms2.root ******
Number of branches in the cache ...: 1093
Cache Efficiency ..................: 0.997372
Cache Efficiency Rel...............: 1.000000
Learn entries......................: 100
Reading............................: 72761843 bytes in 7 transactions
Readahead..........................: 256000 bytes with overhead = 0 bytes
Average transaction................: 10394.549000 Kbytes
Number of blocks in current cache..: 210, total size: 6280352
  • if option = "a" the list of blocks in the cache is printed see also class TTreePerfStats.
  • if option contains 'cachedbranches', the list of branches being cached is printed.

Reimplemented from TFileCacheRead.

Reimplemented in TTreeCacheUnzip.

Definition at line 996 of file TTreeCache.cxx.

◆ ReadBuffer()

Int_t TTreeCache::ReadBuffer ( char *  buf,
Long64_t  pos,
Int_t  len 
)
virtual

Read buffer at position pos if the request is in the list of prefetched blocks read from fBuffer.

Otherwise try to fill the cache from the list of selected branches, and recheck if pos is now in the list. Returns:

  • -1 in case of read failure,
  • 0 in case not in cache,
  • 1 in case read from cache. This function overloads TFileCacheRead::ReadBuffer.

Reimplemented from TFileCacheRead.

Definition at line 1091 of file TTreeCache.cxx.

◆ ReadBufferNormal()

Int_t TTreeCache::ReadBufferNormal ( char *  buf,
Long64_t  pos,
Int_t  len 
)
virtual

Old method ReadBuffer before the addition of the prefetch mechanism.

Definition at line 1022 of file TTreeCache.cxx.

◆ ReadBufferPrefetch()

Int_t TTreeCache::ReadBufferPrefetch ( char *  buf,
Long64_t  pos,
Int_t  len 
)
virtual

Used to read a chunk from a block previously fetched.

It will call FillBuffer even if the cache lookup succeeds, because it will try to prefetch the next block as soon as we start reading from the current block.

Definition at line 1051 of file TTreeCache.cxx.

◆ ResetCache()

void TTreeCache::ResetCache ( )
virtual

This will simply clear the cache.

Reimplemented in TTreeCacheUnzip.

Definition at line 1104 of file TTreeCache.cxx.

◆ SetAutoCreated()

void TTreeCache::SetAutoCreated ( Bool_t  val)
inline

Definition at line 97 of file TTreeCache.h.

◆ SetBufferSize()

Int_t TTreeCache::SetBufferSize ( Int_t  buffersize)
virtual

Change the underlying buffer size of the cache.

If the change of size means some cache content is lost, or if the buffer is now larger, setup for a cache refill the next time there is a read Returns:

  • 0 if the buffer content is still available
  • 1 if some or all of the buffer content has been made unavailable
  • -1 on error

Reimplemented from TFileCacheRead.

Reimplemented in TTreeCacheUnzip.

Definition at line 1123 of file TTreeCache.cxx.

◆ SetEntryRange()

void TTreeCache::SetEntryRange ( Long64_t  emin,
Long64_t  emax 
)
virtual

Set the minimum and maximum entry number to be processed this information helps to optimize the number of baskets to read when prefetching the branch buffers.

Reimplemented in TTreeCacheUnzip.

Definition at line 1156 of file TTreeCache.cxx.

◆ SetFile()

void TTreeCache::SetFile ( TFile file,
TFile::ECacheAction  action = TFile::kDisconnect 
)
virtual

Overload to make sure that the object specific.

Reimplemented from TFileCacheRead.

Definition at line 1178 of file TTreeCache.cxx.

◆ SetLearnEntries()

void TTreeCache::SetLearnEntries ( Int_t  n = 10)
static

Static function to set the number of entries to be used in learning mode The default value for n is 10.

n must be >= 1

Definition at line 1195 of file TTreeCache.cxx.

◆ SetLearnPrefill()

void TTreeCache::SetLearnPrefill ( TTreeCache::EPrefillType  type = kNoPrefill)
virtual

Set whether the learning period is started with a prefilling of the cache and which type of prefilling is used.

The two value currently supported are:

  • TTreeCache::kNoPrefill disable the prefilling
  • TTreeCache::kAllBranches fill the cache with baskets from all branches. The default prefilling behavior can be controlled by setting TTreeCache.Prefill or the environment variable ROOT_TTREECACHE_PREFILL.

Definition at line 1210 of file TTreeCache.cxx.

◆ StartLearningPhase()

void TTreeCache::StartLearningPhase ( )

The name should be enough to explain the method.

The only additional comments is that the cache is cleaned before the new learning phase.

Definition at line 1220 of file TTreeCache.cxx.

◆ StopLearningPhase()

void TTreeCache::StopLearningPhase ( )
virtual

This is the counterpart of StartLearningPhase() and can be used to stop the learning phase.

It's useful when the user knows exactly what branches they are going to use. For the moment it's just a call to FillBuffer() since that method will create the buffer lists from the specified branches.

Reimplemented in TTreeCacheUnzip.

Definition at line 1237 of file TTreeCache.cxx.

◆ UpdateBranches()

void TTreeCache::UpdateBranches ( TTree tree)
virtual

Update pointer to current Tree and recompute pointers to the branches in the cache.

Reimplemented in TTreeCacheUnzip.

Definition at line 1257 of file TTreeCache.cxx.

Member Data Documentation

◆ fAutoCreated

Bool_t TTreeCache::fAutoCreated
protected

! true if cache was automatically created

Definition at line 59 of file TTreeCache.h.

◆ fBranches

TObjArray* TTreeCache::fBranches
protected

! List of branches to be stored in the cache

Definition at line 44 of file TTreeCache.h.

◆ fBrNames

TList* TTreeCache::fBrNames
protected

! list of branch names in the cache

Definition at line 45 of file TTreeCache.h.

◆ fEnabled

Bool_t TTreeCache::fEnabled
protected

! cache enabled for cached reading

Definition at line 56 of file TTreeCache.h.

◆ fEntryCurrent

Long64_t TTreeCache::fEntryCurrent
protected

! current lowest entry number in the cache

Definition at line 38 of file TTreeCache.h.

◆ fEntryMax

Long64_t TTreeCache::fEntryMax
protected

! last entry in the cache

Definition at line 37 of file TTreeCache.h.

◆ fEntryMin

Long64_t TTreeCache::fEntryMin
protected

! first entry in the cache

Definition at line 36 of file TTreeCache.h.

◆ fEntryNext

Long64_t TTreeCache::fEntryNext
protected

! next entry number where cache must be filled

Definition at line 39 of file TTreeCache.h.

◆ fFillTimes

Int_t TTreeCache::fFillTimes
protected

! how many times we can fill the current buffer

Definition at line 52 of file TTreeCache.h.

◆ fFirstBuffer

Bool_t TTreeCache::fFirstBuffer
protected

! true if first buffer is used for prefetching

Definition at line 49 of file TTreeCache.h.

◆ fFirstEntry

Long64_t TTreeCache::fFirstEntry
protected

! save the value of the first entry

Definition at line 54 of file TTreeCache.h.

◆ fFirstTime

Bool_t TTreeCache::fFirstTime
protected

! save the fact that we processes the first entry

Definition at line 53 of file TTreeCache.h.

◆ fgLearnEntries

Int_t TTreeCache::fgLearnEntries = 100
staticprotected

number of entries used for learning mode

Definition at line 58 of file TTreeCache.h.

◆ fIsLearning

Bool_t TTreeCache::fIsLearning
protected

! true if cache is in learning mode

Definition at line 47 of file TTreeCache.h.

◆ fIsManual

Bool_t TTreeCache::fIsManual
protected

! true if cache is StopLearningPhase was used

Definition at line 48 of file TTreeCache.h.

◆ fNbranches

Int_t TTreeCache::fNbranches
protected

! Number of branches in the cache

Definition at line 40 of file TTreeCache.h.

◆ fNReadMiss

Int_t TTreeCache::fNReadMiss
protected

Number of blocks read and not found in the cache.

Definition at line 42 of file TTreeCache.h.

◆ fNReadOk

Int_t TTreeCache::fNReadOk
protected

Number of blocks read and found in the cache.

Definition at line 41 of file TTreeCache.h.

◆ fNReadPref

Int_t TTreeCache::fNReadPref
protected

Number of blocks that were prefetched.

Definition at line 43 of file TTreeCache.h.

◆ fOneTime

Bool_t TTreeCache::fOneTime
protected

! used in the learning phase

Definition at line 50 of file TTreeCache.h.

◆ fPrefillType

EPrefillType TTreeCache::fPrefillType
protected

Whether a pre-filling is enabled (and if applicable which type)

Definition at line 57 of file TTreeCache.h.

◆ fReadDirectionSet

Bool_t TTreeCache::fReadDirectionSet
protected

! read direction established

Definition at line 55 of file TTreeCache.h.

◆ fReverseRead

Bool_t TTreeCache::fReverseRead
protected

! reading in reverse mode

Definition at line 51 of file TTreeCache.h.

◆ fTree

TTree* TTreeCache::fTree
protected

! pointer to the current Tree

Definition at line 46 of file TTreeCache.h.

Libraries for TTreeCache:
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The documentation for this class was generated from the following files: