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.

Special case of a TChain Once the training is done on the first Tree, the list of branches in the cache is kept for the following files.
Special case of a TEventlist if the Tree or TChain has a TEventlist, only the buffers referenced by the list are put in the cache.

The learning period is started or restarted when:

TTree automatically creates a cache. This feature can be controlled with an env. variable or the TTreeCache.Size option.
TTree::SetCacheSize is called with a non-zero size and a cache did not previously exist
TTreeCache::StartLearningPhase is called.
TTreeCache::SetEntryRange is called and the learning is not yet finished and has not been set to manual and the new minimun entry is different.

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

TTreeCache::StopLearningPhase is called.
An entry outside the 'learning' range is requested The 'learning range is from fEntryMin (default to 0) to fEntryMin + fgLearnEntries (default to 100).
A 'cached' TChain switches over to a new file.

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);  //<<<
T->StopCacheLearningPhase();    //<<<
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, kBitMask = 0x00ffffff }

enum	{ kSingleKey = BIT(0), kOverwrite = BIT(1), kWriteDelete = BIT(2) }

enum	EStatusBits { kCanDelete = BIT(0), kMustCleanup = BIT(3), kObjInCanvas = 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 TObjArray *	GetCachedBranches () 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

TTree *	GetTree () 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

TFile *	GetFile () const

virtual Long64_t	GetNoCacheBytesRead () const

virtual Int_t	GetNoCacheReadCalls () const

Int_t	GetNseek () const

Int_t	GetNtot () const

Long64_t	GetPrefetchedBlocks () const

virtual TFilePrefetch *	GetPrefetchObj ()

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...

virtual const char *	ClassName () const
	Returns name of class to which the object belongs. More...

virtual void	Clear (Option_t *="")

virtual TObject *	Clone (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 TObject *	DrawClone (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 TObject *	FindObject (const char *name) const
	Must be redefined in derived classes. More...

virtual TObject *	FindObject (const TObject *obj) const
	Must be redefined in derived classes. More...

virtual Option_t *	GetDrawOption () 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_t *	GetOption () 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...

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...

Bool_t	IsOnHeap () const

virtual Bool_t	IsSortable () const

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...

void *	operator new (size_t sz)

void *	operator new (size_t sz, void *vp)

void *	operator new[] (size_t sz)

void *	operator new[] (size_t sz, void *vp)

TObject &	operator= (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...

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...

TObjArray *	fBranches
	! List of branches to be stored in the cache More...

TList *	fBrNames
	! 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...

TTree *	fTree
	! pointer to the current Tree More...

Protected Attributes inherited from TFileCacheRead
Bool_t	fAsyncReading

Bool_t	fBIsSorted

Bool_t	fBIsTransferred

Int_t *	fBLen
	[fBNb] More...

Int_t	fBNb

Int_t	fBNseek

Int_t	fBNtot

Long64_t *	fBPos
	[fBNb] More...

Long64_t *	fBSeek
	[fBNseek] More...

Int_t *	fBSeekIndex
	[fBNseek] More...

Int_t *	fBSeekLen
	[fBNseek] More...

Int_t *	fBSeekPos
	[fBNseek] More...

Int_t	fBSeekSize

Long64_t *	fBSeekSort
	[fBNseek] More...

Int_t *	fBSeekSortLen
	[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...

TFile *	fFile
	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_t *	fLen
	[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_t *	fPos
	[fNb] start of long buffers More...

TFilePrefetch *	fPrefetch
	! 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_t *	fSeek
	[fNseek] Position on file of buffers to be prefetched More...

Int_t *	fSeekIndex
	[fNseek] sorted index table of fSeek More...

Int_t *	fSeekLen
	[fNseek] Length of buffers to be prefetched More...

Int_t *	fSeekPos
	[fNseek] Position of sorted blocks in fBuffer More...

Int_t	fSeekSize
	Allocated size of fSeek. More...

Long64_t *	fSeekSort
	[fNseek] Position on file of buffers to be prefetched (sorted) More...

Int_t *	fSeekSortLen
	[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 &)

TTreeCache &	operator= (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:

[legend]

Member Enumeration Documentation

◆ EPrefillType

enum TTreeCache::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 940 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 963 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 975 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 987 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 1309 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 1012 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 1107 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 1038 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 1067 of file TTreeCache.cxx.

◆ ResetCache()

void TTreeCache::ResetCache ( )

virtual

This will simply clear the cache.

Reimplemented in TTreeCacheUnzip.

Definition at line 1120 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 1139 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 1172 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 1194 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 1211 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 1226 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 1236 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 1253 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 1273 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.

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

tree/tree/inc/TTreeCache.h
tree/tree/src/TTreeCache.cxx

WHY DO WE NEED the TreeCache when doing data analysis?

HOW TO USE the TreeCache

1. with TTree::Draw

2. with TTree::Process and TSelectors

example 2b

3. with your own event loop

example 3a

example 3b

SPECIAL CASES WHERE TreeCache should not be activated

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

Public Types

Public Member Functions

Static Public Member Functions

Protected Attributes

Static Protected Attributes

Private Member Functions

Additional Inherited Members

Member Enumeration Documentation

◆ EPrefillType

Constructor & Destructor Documentation

◆ TTreeCache() [1/3]

◆ TTreeCache() [2/3]

◆ TTreeCache() [3/3]

◆ ~TTreeCache()

Member Function Documentation

◆ AddBranch() [1/2]

◆ AddBranch() [2/2]

◆ Disable()

◆ DropBranch() [1/2]

◆ DropBranch() [2/2]

◆ Enable()

◆ FillBuffer()

◆ GetCachedBranches()

◆ GetConfiguredPrefillType()

◆ GetEfficiency()

◆ GetEfficiencyRel()

◆ GetEntryMax()

◆ GetEntryMin()

◆ GetLearnEntries()

◆ GetLearnPrefill()

◆ GetTree()

◆ IsAutoCreated()

◆ IsEnabled()

◆ IsLearning()

◆ LearnPrefill()

◆ operator=()

◆ Print()

◆ ReadBuffer()

◆ ReadBufferNormal()

◆ ReadBufferPrefetch()

◆ ResetCache()

◆ SetAutoCreated()

◆ SetBufferSize()

◆ SetEntryRange()

◆ SetFile()

◆ SetLearnEntries()

◆ SetLearnPrefill()

◆ StartLearningPhase()

◆ StopLearningPhase()

◆ UpdateBranches()

Member Data Documentation

◆ fAutoCreated

◆ fBranches

◆ fBrNames

◆ fEnabled

◆ fEntryCurrent

◆ fEntryMax

◆ fEntryMin

◆ fEntryNext

◆ fFillTimes

◆ fFirstBuffer

◆ fFirstEntry

◆ fFirstTime

◆ fgLearnEntries

◆ fIsLearning

◆ fIsManual

◆ fNbranches

◆ fNReadMiss

◆ fNReadOk

◆ fNReadPref