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/*-------------------------------------------------------------------------
*
* logtape.h
* Management of "logical tapes" within temporary files.
*
* See logtape.c for explanations.
*
* Portions Copyright (c) 1996-2023, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
* src/include/utils/logtape.h
*
*-------------------------------------------------------------------------
*/
#ifndef LOGTAPE_H
#define LOGTAPE_H
#include "storage/sharedfileset.h"
/*
* LogicalTapeSet and LogicalTape are opaque types whose details are not
* known outside logtape.c.
*/
typedef struct LogicalTapeSet LogicalTapeSet;
typedef struct LogicalTape LogicalTape;
/*
* The approach tuplesort.c takes to parallel external sorts is that workers,
* whose state is almost the same as independent serial sorts, are made to
* produce a final materialized tape of sorted output in all cases. This is
* frozen, just like any case requiring a final materialized tape. However,
* there is one difference, which is that freezing will also export an
* underlying shared fileset BufFile for sharing. Freezing produces TapeShare
* metadata for the worker when this happens, which is passed along through
* shared memory to leader.
*
* The leader process can then pass an array of TapeShare metadata (one per
* worker participant) to LogicalTapeSetCreate(), alongside a handle to a
* shared fileset, which is sufficient to construct a new logical tapeset that
* consists of each of the tapes materialized by workers.
*
* Note that while logtape.c does create an empty leader tape at the end of the
* tapeset in the leader case, it can never be written to due to a restriction
* in the shared buffile infrastructure.
*/
typedef struct TapeShare
{
/*
* Currently, all the leader process needs is the location of the
* materialized tape's first block.
*/
long firstblocknumber;
} TapeShare;
/*
* prototypes for functions in logtape.c
*/
extern LogicalTapeSet *LogicalTapeSetCreate(bool preallocate,
SharedFileSet *fileset, int worker);
extern void LogicalTapeClose(LogicalTape *lt);
extern void LogicalTapeSetClose(LogicalTapeSet *lts);
extern LogicalTape *LogicalTapeCreate(LogicalTapeSet *lts);
extern LogicalTape *LogicalTapeImport(LogicalTapeSet *lts, int worker, TapeShare *shared);
extern void LogicalTapeSetForgetFreeSpace(LogicalTapeSet *lts);
extern size_t LogicalTapeRead(LogicalTape *lt, void *ptr, size_t size);
extern void LogicalTapeWrite(LogicalTape *lt, const void *ptr, size_t size);
extern void LogicalTapeRewindForRead(LogicalTape *lt, size_t buffer_size);
extern void LogicalTapeFreeze(LogicalTape *lt, TapeShare *share);
extern size_t LogicalTapeBackspace(LogicalTape *lt, size_t size);
extern void LogicalTapeSeek(LogicalTape *lt, long blocknum, int offset);
extern void LogicalTapeTell(LogicalTape *lt, long *blocknum, int *offset);
extern long LogicalTapeSetBlocks(LogicalTapeSet *lts);
#endif /* LOGTAPE_H */
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