codekingpro/portable-devtools

1/*-------------------------------------------------------------------------2 *3 * logtape.h4 *	  Management of "logical tapes" within temporary files.5 *6 * See logtape.c for explanations.7 *8 * Portions Copyright (c) 1996-2023, PostgreSQL Global Development Group9 * Portions Copyright (c) 1994, Regents of the University of California10 *11 * src/include/utils/logtape.h12 *13 *-------------------------------------------------------------------------14 */15 16#ifndef LOGTAPE_H17#define LOGTAPE_H18 19#include "storage/sharedfileset.h"20 21/*22 * LogicalTapeSet and LogicalTape are opaque types whose details are not23 * known outside logtape.c.24 */25typedef struct LogicalTapeSet LogicalTapeSet;26typedef struct LogicalTape LogicalTape;27 28 29/*30 * The approach tuplesort.c takes to parallel external sorts is that workers,31 * whose state is almost the same as independent serial sorts, are made to32 * produce a final materialized tape of sorted output in all cases.  This is33 * frozen, just like any case requiring a final materialized tape.  However,34 * there is one difference, which is that freezing will also export an35 * underlying shared fileset BufFile for sharing.  Freezing produces TapeShare36 * metadata for the worker when this happens, which is passed along through37 * shared memory to leader.38 *39 * The leader process can then pass an array of TapeShare metadata (one per40 * worker participant) to LogicalTapeSetCreate(), alongside a handle to a41 * shared fileset, which is sufficient to construct a new logical tapeset that42 * consists of each of the tapes materialized by workers.43 *44 * Note that while logtape.c does create an empty leader tape at the end of the45 * tapeset in the leader case, it can never be written to due to a restriction46 * in the shared buffile infrastructure.47 */48typedef struct TapeShare49{50	/*51	 * Currently, all the leader process needs is the location of the52	 * materialized tape's first block.53	 */54	long		firstblocknumber;55} TapeShare;56 57/*58 * prototypes for functions in logtape.c59 */60 61extern LogicalTapeSet *LogicalTapeSetCreate(bool preallocate,62											SharedFileSet *fileset, int worker);63extern void LogicalTapeClose(LogicalTape *lt);64extern void LogicalTapeSetClose(LogicalTapeSet *lts);65extern LogicalTape *LogicalTapeCreate(LogicalTapeSet *lts);66extern LogicalTape *LogicalTapeImport(LogicalTapeSet *lts, int worker, TapeShare *shared);67extern void LogicalTapeSetForgetFreeSpace(LogicalTapeSet *lts);68extern size_t LogicalTapeRead(LogicalTape *lt, void *ptr, size_t size);69extern void LogicalTapeWrite(LogicalTape *lt, const void *ptr, size_t size);70extern void LogicalTapeRewindForRead(LogicalTape *lt, size_t buffer_size);71extern void LogicalTapeFreeze(LogicalTape *lt, TapeShare *share);72extern size_t LogicalTapeBackspace(LogicalTape *lt, size_t size);73extern void LogicalTapeSeek(LogicalTape *lt, long blocknum, int offset);74extern void LogicalTapeTell(LogicalTape *lt, long *blocknum, int *offset);75extern long LogicalTapeSetBlocks(LogicalTapeSet *lts);76 77#endif							/* LOGTAPE_H */78