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The single linked list of memory contexts could result in O(N^2) performance to free a set of contexts if they were not freed in reverse order of creation. In many cases the reverse order was used, but there were some significant exceptions that caused real- world performance problems. Rather than requiring all callers to care about the order in which contexts were freed, and hunting down and changing all existing cases where the wrong order was used, we add one pointer per memory context so that the implementation details are not so visible. Jan Wieck
102 lines
3.6 KiB
C
102 lines
3.6 KiB
C
/*-------------------------------------------------------------------------
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*
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* memnodes.h
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* POSTGRES memory context node definitions.
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*
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*
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* Portions Copyright (c) 1996-2015, PostgreSQL Global Development Group
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* Portions Copyright (c) 1994, Regents of the University of California
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*
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* src/include/nodes/memnodes.h
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*
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*-------------------------------------------------------------------------
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*/
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#ifndef MEMNODES_H
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#define MEMNODES_H
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#include "nodes/nodes.h"
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/*
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* MemoryContextCounters
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* Summarization state for MemoryContextStats collection.
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*
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* The set of counters in this struct is biased towards AllocSet; if we ever
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* add any context types that are based on fundamentally different approaches,
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* we might need more or different counters here. A possible API spec then
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* would be to print only nonzero counters, but for now we just summarize in
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* the format historically used by AllocSet.
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*/
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typedef struct MemoryContextCounters
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{
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Size nblocks; /* Total number of malloc blocks */
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Size freechunks; /* Total number of free chunks */
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Size totalspace; /* Total bytes requested from malloc */
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Size freespace; /* The unused portion of totalspace */
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} MemoryContextCounters;
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/*
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* MemoryContext
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* A logical context in which memory allocations occur.
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*
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* MemoryContext itself is an abstract type that can have multiple
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* implementations, though for now we have only AllocSetContext.
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* The function pointers in MemoryContextMethods define one specific
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* implementation of MemoryContext --- they are a virtual function table
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* in C++ terms.
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*
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* Node types that are actual implementations of memory contexts must
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* begin with the same fields as MemoryContext.
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*
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* Note: for largely historical reasons, typedef MemoryContext is a pointer
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* to the context struct rather than the struct type itself.
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*/
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typedef struct MemoryContextMethods
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{
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void *(*alloc) (MemoryContext context, Size size);
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/* call this free_p in case someone #define's free() */
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void (*free_p) (MemoryContext context, void *pointer);
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void *(*realloc) (MemoryContext context, void *pointer, Size size);
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void (*init) (MemoryContext context);
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void (*reset) (MemoryContext context);
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void (*delete_context) (MemoryContext context);
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Size (*get_chunk_space) (MemoryContext context, void *pointer);
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bool (*is_empty) (MemoryContext context);
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void (*stats) (MemoryContext context, int level, bool print,
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MemoryContextCounters *totals);
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#ifdef MEMORY_CONTEXT_CHECKING
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void (*check) (MemoryContext context);
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#endif
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} MemoryContextMethods;
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typedef struct MemoryContextData
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{
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NodeTag type; /* identifies exact kind of context */
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/* these two fields are placed here to minimize alignment wastage: */
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bool isReset; /* T = no space alloced since last reset */
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bool allowInCritSection; /* allow palloc in critical section */
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MemoryContextMethods *methods; /* virtual function table */
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MemoryContext parent; /* NULL if no parent (toplevel context) */
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MemoryContext firstchild; /* head of linked list of children */
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MemoryContext prevchild; /* previous child of same parent */
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MemoryContext nextchild; /* next child of same parent */
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char *name; /* context name (just for debugging) */
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MemoryContextCallback *reset_cbs; /* list of reset/delete callbacks */
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} MemoryContextData;
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/* utils/palloc.h contains typedef struct MemoryContextData *MemoryContext */
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/*
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* MemoryContextIsValid
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* True iff memory context is valid.
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*
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* Add new context types to the set accepted by this macro.
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*/
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#define MemoryContextIsValid(context) \
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((context) != NULL && \
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(IsA((context), AllocSetContext)))
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#endif /* MEMNODES_H */
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