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1017 lines
30 KiB
C
1017 lines
30 KiB
C
/*-------------------------------------------------------------------------
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*
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* logtape.c
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* Management of "logical tapes" within temporary files.
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*
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* This module exists to support sorting via multiple merge passes (see
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* tuplesort.c). Merging is an ideal algorithm for tape devices, but if
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* we implement it on disk by creating a separate file for each "tape",
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* there is an annoying problem: the peak space usage is at least twice
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* the volume of actual data to be sorted. (This must be so because each
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* datum will appear in both the input and output tapes of the final
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* merge pass. For seven-tape polyphase merge, which is otherwise a
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* pretty good algorithm, peak usage is more like 4x actual data volume.)
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*
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* We can work around this problem by recognizing that any one tape
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* dataset (with the possible exception of the final output) is written
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* and read exactly once in a perfectly sequential manner. Therefore,
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* a datum once read will not be required again, and we can recycle its
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* space for use by the new tape dataset(s) being generated. In this way,
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* the total space usage is essentially just the actual data volume, plus
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* insignificant bookkeeping and start/stop overhead.
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*
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* Few OSes allow arbitrary parts of a file to be released back to the OS,
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* so we have to implement this space-recycling ourselves within a single
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* logical file. logtape.c exists to perform this bookkeeping and provide
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* the illusion of N independent tape devices to tuplesort.c. Note that
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* logtape.c itself depends on buffile.c to provide a "logical file" of
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* larger size than the underlying OS may support.
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*
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* For simplicity, we allocate and release space in the underlying file
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* in BLCKSZ-size blocks. Space allocation boils down to keeping track
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* of which blocks in the underlying file belong to which logical tape,
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* plus any blocks that are free (recycled and not yet reused).
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* The blocks in each logical tape are remembered using a method borrowed
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* from the Unix HFS filesystem: we store data block numbers in an
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* "indirect block". If an indirect block fills up, we write it out to
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* the underlying file and remember its location in a second-level indirect
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* block. In the same way second-level blocks are remembered in third-
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* level blocks, and so on if necessary (of course we're talking huge
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* amounts of data here). The topmost indirect block of a given logical
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* tape is never actually written out to the physical file, but all lower-
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* level indirect blocks will be.
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*
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* The initial write pass is guaranteed to fill the underlying file
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* perfectly sequentially, no matter how data is divided into logical tapes.
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* Once we begin merge passes, the access pattern becomes considerably
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* less predictable --- but the seeking involved should be comparable to
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* what would happen if we kept each logical tape in a separate file,
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* so there's no serious performance penalty paid to obtain the space
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* savings of recycling. We try to localize the write accesses by always
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* writing to the lowest-numbered free block when we have a choice; it's
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* not clear this helps much, but it can't hurt. (XXX perhaps a LIFO
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* policy for free blocks would be better?)
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*
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* To support the above policy of writing to the lowest free block,
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* ltsGetFreeBlock sorts the list of free block numbers into decreasing
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* order each time it is asked for a block and the list isn't currently
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* sorted. This is an efficient way to handle it because we expect cycles
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* of releasing many blocks followed by re-using many blocks, due to
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* tuplesort.c's "preread" behavior.
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*
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* Since all the bookkeeping and buffer memory is allocated with palloc(),
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* and the underlying file(s) are made with OpenTemporaryFile, all resources
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* for a logical tape set are certain to be cleaned up even if processing
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* is aborted by ereport(ERROR). To avoid confusion, the caller should take
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* care that all calls for a single LogicalTapeSet are made in the same
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* palloc context.
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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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* IDENTIFICATION
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* src/backend/utils/sort/logtape.c
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*
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*-------------------------------------------------------------------------
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*/
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#include "postgres.h"
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#include "storage/buffile.h"
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#include "utils/logtape.h"
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/*
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* Block indexes are "long"s, so we can fit this many per indirect block.
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* NB: we assume this is an exact fit!
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*/
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#define BLOCKS_PER_INDIR_BLOCK ((int) (BLCKSZ / sizeof(long)))
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/*
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* We use a struct like this for each active indirection level of each
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* logical tape. If the indirect block is not the highest level of its
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* tape, the "nextup" link points to the next higher level. Only the
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* "ptrs" array is written out if we have to dump the indirect block to
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* disk. If "ptrs" is not completely full, we store -1L in the first
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* unused slot at completion of the write phase for the logical tape.
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*/
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typedef struct IndirectBlock
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{
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int nextSlot; /* next pointer slot to write or read */
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struct IndirectBlock *nextup; /* parent indirect level, or NULL if
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* top */
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long ptrs[BLOCKS_PER_INDIR_BLOCK]; /* indexes of contained blocks */
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} IndirectBlock;
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/*
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* This data structure represents a single "logical tape" within the set
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* of logical tapes stored in the same file. We must keep track of the
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* current partially-read-or-written data block as well as the active
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* indirect block level(s).
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*/
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typedef struct LogicalTape
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{
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IndirectBlock *indirect; /* bottom of my indirect-block hierarchy */
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bool writing; /* T while in write phase */
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bool frozen; /* T if blocks should not be freed when read */
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bool dirty; /* does buffer need to be written? */
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/*
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* The total data volume in the logical tape is numFullBlocks * BLCKSZ +
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* lastBlockBytes. BUT: we do not update lastBlockBytes during writing,
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* only at completion of a write phase.
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*/
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long numFullBlocks; /* number of complete blocks in log tape */
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int lastBlockBytes; /* valid bytes in last (incomplete) block */
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/*
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* Buffer for current data block. Note we don't bother to store the
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* actual file block number of the data block (during the write phase it
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* hasn't been assigned yet, and during read we don't care anymore). But
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* we do need the relative block number so we can detect end-of-tape while
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* reading.
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*/
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char *buffer; /* physical buffer (separately palloc'd) */
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long curBlockNumber; /* this block's logical blk# within tape */
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int pos; /* next read/write position in buffer */
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int nbytes; /* total # of valid bytes in buffer */
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} LogicalTape;
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/*
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* This data structure represents a set of related "logical tapes" sharing
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* space in a single underlying file. (But that "file" may be multiple files
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* if needed to escape OS limits on file size; buffile.c handles that for us.)
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* The number of tapes is fixed at creation.
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*/
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struct LogicalTapeSet
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{
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BufFile *pfile; /* underlying file for whole tape set */
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long nFileBlocks; /* # of blocks used in underlying file */
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/*
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* We store the numbers of recycled-and-available blocks in freeBlocks[].
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* When there are no such blocks, we extend the underlying file.
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*
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* If forgetFreeSpace is true then any freed blocks are simply forgotten
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* rather than being remembered in freeBlocks[]. See notes for
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* LogicalTapeSetForgetFreeSpace().
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*
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* If blocksSorted is true then the block numbers in freeBlocks are in
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* *decreasing* order, so that removing the last entry gives us the lowest
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* free block. We re-sort the blocks whenever a block is demanded; this
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* should be reasonably efficient given the expected usage pattern.
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*/
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bool forgetFreeSpace; /* are we remembering free blocks? */
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bool blocksSorted; /* is freeBlocks[] currently in order? */
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long *freeBlocks; /* resizable array */
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int nFreeBlocks; /* # of currently free blocks */
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int freeBlocksLen; /* current allocated length of freeBlocks[] */
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/* The array of logical tapes. */
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int nTapes; /* # of logical tapes in set */
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LogicalTape tapes[FLEXIBLE_ARRAY_MEMBER]; /* has nTapes nentries */
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};
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static void ltsWriteBlock(LogicalTapeSet *lts, long blocknum, void *buffer);
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static void ltsReadBlock(LogicalTapeSet *lts, long blocknum, void *buffer);
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static long ltsGetFreeBlock(LogicalTapeSet *lts);
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static void ltsReleaseBlock(LogicalTapeSet *lts, long blocknum);
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static void ltsRecordBlockNum(LogicalTapeSet *lts, IndirectBlock *indirect,
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long blocknum);
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static long ltsRewindIndirectBlock(LogicalTapeSet *lts,
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IndirectBlock *indirect,
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bool freezing);
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static long ltsRewindFrozenIndirectBlock(LogicalTapeSet *lts,
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IndirectBlock *indirect);
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static long ltsRecallNextBlockNum(LogicalTapeSet *lts,
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IndirectBlock *indirect,
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bool frozen);
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static long ltsRecallPrevBlockNum(LogicalTapeSet *lts,
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IndirectBlock *indirect);
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static void ltsDumpBuffer(LogicalTapeSet *lts, LogicalTape *lt);
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/*
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* Write a block-sized buffer to the specified block of the underlying file.
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*
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* NB: should not attempt to write beyond current end of file (ie, create
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* "holes" in file), since BufFile doesn't allow that. The first write pass
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* must write blocks sequentially.
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*
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* No need for an error return convention; we ereport() on any error.
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*/
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static void
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ltsWriteBlock(LogicalTapeSet *lts, long blocknum, void *buffer)
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{
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if (BufFileSeekBlock(lts->pfile, blocknum) != 0 ||
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BufFileWrite(lts->pfile, buffer, BLCKSZ) != BLCKSZ)
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ereport(ERROR,
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(errcode_for_file_access(),
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errmsg("could not write block %ld of temporary file: %m",
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blocknum)));
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}
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/*
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* Read a block-sized buffer from the specified block of the underlying file.
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*
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* No need for an error return convention; we ereport() on any error. This
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* module should never attempt to read a block it doesn't know is there.
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*/
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static void
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ltsReadBlock(LogicalTapeSet *lts, long blocknum, void *buffer)
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{
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if (BufFileSeekBlock(lts->pfile, blocknum) != 0 ||
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BufFileRead(lts->pfile, buffer, BLCKSZ) != BLCKSZ)
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ereport(ERROR,
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(errcode_for_file_access(),
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errmsg("could not read block %ld of temporary file: %m",
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blocknum)));
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}
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/*
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* qsort comparator for sorting freeBlocks[] into decreasing order.
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*/
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static int
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freeBlocks_cmp(const void *a, const void *b)
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{
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long ablk = *((const long *) a);
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long bblk = *((const long *) b);
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/* can't just subtract because long might be wider than int */
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if (ablk < bblk)
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return 1;
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if (ablk > bblk)
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return -1;
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return 0;
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}
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/*
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* Select a currently unused block for writing to.
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*
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* NB: should only be called when writer is ready to write immediately,
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* to ensure that first write pass is sequential.
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*/
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static long
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ltsGetFreeBlock(LogicalTapeSet *lts)
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{
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/*
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* If there are multiple free blocks, we select the one appearing last in
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* freeBlocks[] (after sorting the array if needed). If there are none,
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* assign the next block at the end of the file.
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*/
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if (lts->nFreeBlocks > 0)
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{
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if (!lts->blocksSorted)
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{
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qsort((void *) lts->freeBlocks, lts->nFreeBlocks,
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sizeof(long), freeBlocks_cmp);
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lts->blocksSorted = true;
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}
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return lts->freeBlocks[--lts->nFreeBlocks];
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}
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else
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return lts->nFileBlocks++;
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}
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/*
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* Return a block# to the freelist.
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*/
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static void
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ltsReleaseBlock(LogicalTapeSet *lts, long blocknum)
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{
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int ndx;
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/*
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* Do nothing if we're no longer interested in remembering free space.
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*/
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if (lts->forgetFreeSpace)
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return;
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/*
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* Enlarge freeBlocks array if full.
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*/
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if (lts->nFreeBlocks >= lts->freeBlocksLen)
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{
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lts->freeBlocksLen *= 2;
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lts->freeBlocks = (long *) repalloc(lts->freeBlocks,
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lts->freeBlocksLen * sizeof(long));
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}
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/*
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* Add blocknum to array, and mark the array unsorted if it's no longer in
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* decreasing order.
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*/
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ndx = lts->nFreeBlocks++;
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lts->freeBlocks[ndx] = blocknum;
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if (ndx > 0 && lts->freeBlocks[ndx - 1] < blocknum)
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lts->blocksSorted = false;
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}
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/*
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* These routines manipulate indirect-block hierarchies. All are recursive
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* so that they don't have any specific limit on the depth of hierarchy.
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*/
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/*
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* Record a data block number in a logical tape's lowest indirect block,
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* or record an indirect block's number in the next higher indirect level.
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*/
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static void
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ltsRecordBlockNum(LogicalTapeSet *lts, IndirectBlock *indirect,
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long blocknum)
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{
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if (indirect->nextSlot >= BLOCKS_PER_INDIR_BLOCK)
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{
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/*
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* This indirect block is full, so dump it out and recursively save
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* its address in the next indirection level. Create a new
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* indirection level if there wasn't one before.
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*/
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long indirblock = ltsGetFreeBlock(lts);
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ltsWriteBlock(lts, indirblock, (void *) indirect->ptrs);
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if (indirect->nextup == NULL)
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{
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indirect->nextup = (IndirectBlock *) palloc(sizeof(IndirectBlock));
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indirect->nextup->nextSlot = 0;
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indirect->nextup->nextup = NULL;
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}
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ltsRecordBlockNum(lts, indirect->nextup, indirblock);
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/*
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* Reset to fill another indirect block at this level.
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*/
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indirect->nextSlot = 0;
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}
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indirect->ptrs[indirect->nextSlot++] = blocknum;
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}
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/*
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* Reset a logical tape's indirect-block hierarchy after a write pass
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* to prepare for reading. We dump out partly-filled blocks except
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* at the top of the hierarchy, and we rewind each level to the start.
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* This call returns the first data block number, or -1L if the tape
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* is empty.
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*
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* Unless 'freezing' is true, release indirect blocks to the free pool after
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* reading them.
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*/
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static long
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ltsRewindIndirectBlock(LogicalTapeSet *lts,
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IndirectBlock *indirect,
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bool freezing)
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{
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/* Handle case of never-written-to tape */
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if (indirect == NULL)
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return -1L;
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/* Insert sentinel if block is not full */
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if (indirect->nextSlot < BLOCKS_PER_INDIR_BLOCK)
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indirect->ptrs[indirect->nextSlot] = -1L;
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/*
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* If block is not topmost, write it out, and recurse to obtain address of
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* first block in this hierarchy level. Read that one in.
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*/
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if (indirect->nextup != NULL)
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{
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long indirblock = ltsGetFreeBlock(lts);
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ltsWriteBlock(lts, indirblock, (void *) indirect->ptrs);
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ltsRecordBlockNum(lts, indirect->nextup, indirblock);
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indirblock = ltsRewindIndirectBlock(lts, indirect->nextup, freezing);
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Assert(indirblock != -1L);
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ltsReadBlock(lts, indirblock, (void *) indirect->ptrs);
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if (!freezing)
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ltsReleaseBlock(lts, indirblock);
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}
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/*
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* Reset my next-block pointer, and then fetch a block number if any.
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*/
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indirect->nextSlot = 0;
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if (indirect->ptrs[0] == -1L)
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return -1L;
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return indirect->ptrs[indirect->nextSlot++];
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}
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/*
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* Rewind a previously-frozen indirect-block hierarchy for another read pass.
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* This call returns the first data block number, or -1L if the tape
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* is empty.
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*/
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static long
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ltsRewindFrozenIndirectBlock(LogicalTapeSet *lts,
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IndirectBlock *indirect)
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{
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/* Handle case of never-written-to tape */
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if (indirect == NULL)
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return -1L;
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/*
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* If block is not topmost, recurse to obtain address of first block in
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* this hierarchy level. Read that one in.
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*/
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if (indirect->nextup != NULL)
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{
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long indirblock;
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indirblock = ltsRewindFrozenIndirectBlock(lts, indirect->nextup);
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Assert(indirblock != -1L);
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ltsReadBlock(lts, indirblock, (void *) indirect->ptrs);
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}
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/*
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* Reset my next-block pointer, and then fetch a block number if any.
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*/
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indirect->nextSlot = 0;
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if (indirect->ptrs[0] == -1L)
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return -1L;
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return indirect->ptrs[indirect->nextSlot++];
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}
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/*
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* Obtain next data block number in the forward direction, or -1L if no more.
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*
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* Unless 'frozen' is true, release indirect blocks to the free pool after
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* reading them.
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*/
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static long
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ltsRecallNextBlockNum(LogicalTapeSet *lts,
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IndirectBlock *indirect,
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bool frozen)
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{
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/* Handle case of never-written-to tape */
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if (indirect == NULL)
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return -1L;
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if (indirect->nextSlot >= BLOCKS_PER_INDIR_BLOCK ||
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indirect->ptrs[indirect->nextSlot] == -1L)
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{
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long indirblock;
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if (indirect->nextup == NULL)
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return -1L; /* nothing left at this level */
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indirblock = ltsRecallNextBlockNum(lts, indirect->nextup, frozen);
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if (indirblock == -1L)
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return -1L; /* nothing left at this level */
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ltsReadBlock(lts, indirblock, (void *) indirect->ptrs);
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if (!frozen)
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ltsReleaseBlock(lts, indirblock);
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indirect->nextSlot = 0;
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}
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if (indirect->ptrs[indirect->nextSlot] == -1L)
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return -1L;
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return indirect->ptrs[indirect->nextSlot++];
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}
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|
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/*
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* Obtain next data block number in the reverse direction, or -1L if no more.
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*
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* Note this fetches the block# before the one last returned, no matter which
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* direction of call returned that one. If we fail, no change in state.
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*
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* This routine can only be used in 'frozen' state, so there's no need to
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* pass a parameter telling whether to release blocks ... we never do.
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*/
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static long
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ltsRecallPrevBlockNum(LogicalTapeSet *lts,
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IndirectBlock *indirect)
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{
|
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/* Handle case of never-written-to tape */
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if (indirect == NULL)
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return -1L;
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|
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if (indirect->nextSlot <= 1)
|
|
{
|
|
long indirblock;
|
|
|
|
if (indirect->nextup == NULL)
|
|
return -1L; /* nothing left at this level */
|
|
indirblock = ltsRecallPrevBlockNum(lts, indirect->nextup);
|
|
if (indirblock == -1L)
|
|
return -1L; /* nothing left at this level */
|
|
ltsReadBlock(lts, indirblock, (void *) indirect->ptrs);
|
|
|
|
/*
|
|
* The previous block would only have been written out if full, so we
|
|
* need not search it for a -1 sentinel.
|
|
*/
|
|
indirect->nextSlot = BLOCKS_PER_INDIR_BLOCK + 1;
|
|
}
|
|
indirect->nextSlot--;
|
|
return indirect->ptrs[indirect->nextSlot - 1];
|
|
}
|
|
|
|
|
|
/*
|
|
* Create a set of logical tapes in a temporary underlying file.
|
|
*
|
|
* Each tape is initialized in write state.
|
|
*/
|
|
LogicalTapeSet *
|
|
LogicalTapeSetCreate(int ntapes)
|
|
{
|
|
LogicalTapeSet *lts;
|
|
LogicalTape *lt;
|
|
int i;
|
|
|
|
/*
|
|
* Create top-level struct including per-tape LogicalTape structs.
|
|
*/
|
|
Assert(ntapes > 0);
|
|
lts = (LogicalTapeSet *) palloc(offsetof(LogicalTapeSet, tapes) +
|
|
ntapes * sizeof(LogicalTape));
|
|
lts->pfile = BufFileCreateTemp(false);
|
|
lts->nFileBlocks = 0L;
|
|
lts->forgetFreeSpace = false;
|
|
lts->blocksSorted = true; /* a zero-length array is sorted ... */
|
|
lts->freeBlocksLen = 32; /* reasonable initial guess */
|
|
lts->freeBlocks = (long *) palloc(lts->freeBlocksLen * sizeof(long));
|
|
lts->nFreeBlocks = 0;
|
|
lts->nTapes = ntapes;
|
|
|
|
/*
|
|
* Initialize per-tape structs. Note we allocate the I/O buffer and
|
|
* first-level indirect block for a tape only when it is first actually
|
|
* written to. This avoids wasting memory space when tuplesort.c
|
|
* overestimates the number of tapes needed.
|
|
*/
|
|
for (i = 0; i < ntapes; i++)
|
|
{
|
|
lt = <s->tapes[i];
|
|
lt->indirect = NULL;
|
|
lt->writing = true;
|
|
lt->frozen = false;
|
|
lt->dirty = false;
|
|
lt->numFullBlocks = 0L;
|
|
lt->lastBlockBytes = 0;
|
|
lt->buffer = NULL;
|
|
lt->curBlockNumber = 0L;
|
|
lt->pos = 0;
|
|
lt->nbytes = 0;
|
|
}
|
|
return lts;
|
|
}
|
|
|
|
/*
|
|
* Close a logical tape set and release all resources.
|
|
*/
|
|
void
|
|
LogicalTapeSetClose(LogicalTapeSet *lts)
|
|
{
|
|
LogicalTape *lt;
|
|
IndirectBlock *ib,
|
|
*nextib;
|
|
int i;
|
|
|
|
BufFileClose(lts->pfile);
|
|
for (i = 0; i < lts->nTapes; i++)
|
|
{
|
|
lt = <s->tapes[i];
|
|
for (ib = lt->indirect; ib != NULL; ib = nextib)
|
|
{
|
|
nextib = ib->nextup;
|
|
pfree(ib);
|
|
}
|
|
if (lt->buffer)
|
|
pfree(lt->buffer);
|
|
}
|
|
pfree(lts->freeBlocks);
|
|
pfree(lts);
|
|
}
|
|
|
|
/*
|
|
* Mark a logical tape set as not needing management of free space anymore.
|
|
*
|
|
* This should be called if the caller does not intend to write any more data
|
|
* into the tape set, but is reading from un-frozen tapes. Since no more
|
|
* writes are planned, remembering free blocks is no longer useful. Setting
|
|
* this flag lets us avoid wasting time and space in ltsReleaseBlock(), which
|
|
* is not designed to handle large numbers of free blocks.
|
|
*/
|
|
void
|
|
LogicalTapeSetForgetFreeSpace(LogicalTapeSet *lts)
|
|
{
|
|
lts->forgetFreeSpace = true;
|
|
}
|
|
|
|
/*
|
|
* Dump the dirty buffer of a logical tape.
|
|
*/
|
|
static void
|
|
ltsDumpBuffer(LogicalTapeSet *lts, LogicalTape *lt)
|
|
{
|
|
long datablock = ltsGetFreeBlock(lts);
|
|
|
|
Assert(lt->dirty);
|
|
ltsWriteBlock(lts, datablock, (void *) lt->buffer);
|
|
ltsRecordBlockNum(lts, lt->indirect, datablock);
|
|
lt->dirty = false;
|
|
/* Caller must do other state update as needed */
|
|
}
|
|
|
|
/*
|
|
* Write to a logical tape.
|
|
*
|
|
* There are no error returns; we ereport() on failure.
|
|
*/
|
|
void
|
|
LogicalTapeWrite(LogicalTapeSet *lts, int tapenum,
|
|
void *ptr, size_t size)
|
|
{
|
|
LogicalTape *lt;
|
|
size_t nthistime;
|
|
|
|
Assert(tapenum >= 0 && tapenum < lts->nTapes);
|
|
lt = <s->tapes[tapenum];
|
|
Assert(lt->writing);
|
|
|
|
/* Allocate data buffer and first indirect block on first write */
|
|
if (lt->buffer == NULL)
|
|
lt->buffer = (char *) palloc(BLCKSZ);
|
|
if (lt->indirect == NULL)
|
|
{
|
|
lt->indirect = (IndirectBlock *) palloc(sizeof(IndirectBlock));
|
|
lt->indirect->nextSlot = 0;
|
|
lt->indirect->nextup = NULL;
|
|
}
|
|
|
|
while (size > 0)
|
|
{
|
|
if (lt->pos >= BLCKSZ)
|
|
{
|
|
/* Buffer full, dump it out */
|
|
if (lt->dirty)
|
|
ltsDumpBuffer(lts, lt);
|
|
else
|
|
{
|
|
/* Hmm, went directly from reading to writing? */
|
|
elog(ERROR, "invalid logtape state: should be dirty");
|
|
}
|
|
lt->numFullBlocks++;
|
|
lt->curBlockNumber++;
|
|
lt->pos = 0;
|
|
lt->nbytes = 0;
|
|
}
|
|
|
|
nthistime = BLCKSZ - lt->pos;
|
|
if (nthistime > size)
|
|
nthistime = size;
|
|
Assert(nthistime > 0);
|
|
|
|
memcpy(lt->buffer + lt->pos, ptr, nthistime);
|
|
|
|
lt->dirty = true;
|
|
lt->pos += nthistime;
|
|
if (lt->nbytes < lt->pos)
|
|
lt->nbytes = lt->pos;
|
|
ptr = (void *) ((char *) ptr + nthistime);
|
|
size -= nthistime;
|
|
}
|
|
}
|
|
|
|
/*
|
|
* Rewind logical tape and switch from writing to reading or vice versa.
|
|
*
|
|
* Unless the tape has been "frozen" in read state, forWrite must be the
|
|
* opposite of the previous tape state.
|
|
*/
|
|
void
|
|
LogicalTapeRewind(LogicalTapeSet *lts, int tapenum, bool forWrite)
|
|
{
|
|
LogicalTape *lt;
|
|
long datablocknum;
|
|
|
|
Assert(tapenum >= 0 && tapenum < lts->nTapes);
|
|
lt = <s->tapes[tapenum];
|
|
|
|
if (!forWrite)
|
|
{
|
|
if (lt->writing)
|
|
{
|
|
/*
|
|
* Completion of a write phase. Flush last partial data block,
|
|
* flush any partial indirect blocks, rewind for normal
|
|
* (destructive) read.
|
|
*/
|
|
if (lt->dirty)
|
|
ltsDumpBuffer(lts, lt);
|
|
lt->lastBlockBytes = lt->nbytes;
|
|
lt->writing = false;
|
|
datablocknum = ltsRewindIndirectBlock(lts, lt->indirect, false);
|
|
}
|
|
else
|
|
{
|
|
/*
|
|
* This is only OK if tape is frozen; we rewind for (another) read
|
|
* pass.
|
|
*/
|
|
Assert(lt->frozen);
|
|
datablocknum = ltsRewindFrozenIndirectBlock(lts, lt->indirect);
|
|
}
|
|
/* Read the first block, or reset if tape is empty */
|
|
lt->curBlockNumber = 0L;
|
|
lt->pos = 0;
|
|
lt->nbytes = 0;
|
|
if (datablocknum != -1L)
|
|
{
|
|
ltsReadBlock(lts, datablocknum, (void *) lt->buffer);
|
|
if (!lt->frozen)
|
|
ltsReleaseBlock(lts, datablocknum);
|
|
lt->nbytes = (lt->curBlockNumber < lt->numFullBlocks) ?
|
|
BLCKSZ : lt->lastBlockBytes;
|
|
}
|
|
}
|
|
else
|
|
{
|
|
/*
|
|
* Completion of a read phase. Rewind and prepare for write.
|
|
*
|
|
* NOTE: we assume the caller has read the tape to the end; otherwise
|
|
* untouched data and indirect blocks will not have been freed. We
|
|
* could add more code to free any unread blocks, but in current usage
|
|
* of this module it'd be useless code.
|
|
*/
|
|
IndirectBlock *ib,
|
|
*nextib;
|
|
|
|
Assert(!lt->writing && !lt->frozen);
|
|
/* Must truncate the indirect-block hierarchy down to one level. */
|
|
if (lt->indirect)
|
|
{
|
|
for (ib = lt->indirect->nextup; ib != NULL; ib = nextib)
|
|
{
|
|
nextib = ib->nextup;
|
|
pfree(ib);
|
|
}
|
|
lt->indirect->nextSlot = 0;
|
|
lt->indirect->nextup = NULL;
|
|
}
|
|
lt->writing = true;
|
|
lt->dirty = false;
|
|
lt->numFullBlocks = 0L;
|
|
lt->lastBlockBytes = 0;
|
|
lt->curBlockNumber = 0L;
|
|
lt->pos = 0;
|
|
lt->nbytes = 0;
|
|
}
|
|
}
|
|
|
|
/*
|
|
* Read from a logical tape.
|
|
*
|
|
* Early EOF is indicated by return value less than #bytes requested.
|
|
*/
|
|
size_t
|
|
LogicalTapeRead(LogicalTapeSet *lts, int tapenum,
|
|
void *ptr, size_t size)
|
|
{
|
|
LogicalTape *lt;
|
|
size_t nread = 0;
|
|
size_t nthistime;
|
|
|
|
Assert(tapenum >= 0 && tapenum < lts->nTapes);
|
|
lt = <s->tapes[tapenum];
|
|
Assert(!lt->writing);
|
|
|
|
while (size > 0)
|
|
{
|
|
if (lt->pos >= lt->nbytes)
|
|
{
|
|
/* Try to load more data into buffer. */
|
|
long datablocknum = ltsRecallNextBlockNum(lts, lt->indirect,
|
|
lt->frozen);
|
|
|
|
if (datablocknum == -1L)
|
|
break; /* EOF */
|
|
lt->curBlockNumber++;
|
|
lt->pos = 0;
|
|
ltsReadBlock(lts, datablocknum, (void *) lt->buffer);
|
|
if (!lt->frozen)
|
|
ltsReleaseBlock(lts, datablocknum);
|
|
lt->nbytes = (lt->curBlockNumber < lt->numFullBlocks) ?
|
|
BLCKSZ : lt->lastBlockBytes;
|
|
if (lt->nbytes <= 0)
|
|
break; /* EOF (possible here?) */
|
|
}
|
|
|
|
nthistime = lt->nbytes - lt->pos;
|
|
if (nthistime > size)
|
|
nthistime = size;
|
|
Assert(nthistime > 0);
|
|
|
|
memcpy(ptr, lt->buffer + lt->pos, nthistime);
|
|
|
|
lt->pos += nthistime;
|
|
ptr = (void *) ((char *) ptr + nthistime);
|
|
size -= nthistime;
|
|
nread += nthistime;
|
|
}
|
|
|
|
return nread;
|
|
}
|
|
|
|
/*
|
|
* "Freeze" the contents of a tape so that it can be read multiple times
|
|
* and/or read backwards. Once a tape is frozen, its contents will not
|
|
* be released until the LogicalTapeSet is destroyed. This is expected
|
|
* to be used only for the final output pass of a merge.
|
|
*
|
|
* This *must* be called just at the end of a write pass, before the
|
|
* tape is rewound (after rewind is too late!). It performs a rewind
|
|
* and switch to read mode "for free". An immediately following rewind-
|
|
* for-read call is OK but not necessary.
|
|
*/
|
|
void
|
|
LogicalTapeFreeze(LogicalTapeSet *lts, int tapenum)
|
|
{
|
|
LogicalTape *lt;
|
|
long datablocknum;
|
|
|
|
Assert(tapenum >= 0 && tapenum < lts->nTapes);
|
|
lt = <s->tapes[tapenum];
|
|
Assert(lt->writing);
|
|
|
|
/*
|
|
* Completion of a write phase. Flush last partial data block, flush any
|
|
* partial indirect blocks, rewind for nondestructive read.
|
|
*/
|
|
if (lt->dirty)
|
|
ltsDumpBuffer(lts, lt);
|
|
lt->lastBlockBytes = lt->nbytes;
|
|
lt->writing = false;
|
|
lt->frozen = true;
|
|
datablocknum = ltsRewindIndirectBlock(lts, lt->indirect, true);
|
|
/* Read the first block, or reset if tape is empty */
|
|
lt->curBlockNumber = 0L;
|
|
lt->pos = 0;
|
|
lt->nbytes = 0;
|
|
if (datablocknum != -1L)
|
|
{
|
|
ltsReadBlock(lts, datablocknum, (void *) lt->buffer);
|
|
lt->nbytes = (lt->curBlockNumber < lt->numFullBlocks) ?
|
|
BLCKSZ : lt->lastBlockBytes;
|
|
}
|
|
}
|
|
|
|
/*
|
|
* Backspace the tape a given number of bytes. (We also support a more
|
|
* general seek interface, see below.)
|
|
*
|
|
* *Only* a frozen-for-read tape can be backed up; we don't support
|
|
* random access during write, and an unfrozen read tape may have
|
|
* already discarded the desired data!
|
|
*
|
|
* Return value is TRUE if seek successful, FALSE if there isn't that much
|
|
* data before the current point (in which case there's no state change).
|
|
*/
|
|
bool
|
|
LogicalTapeBackspace(LogicalTapeSet *lts, int tapenum, size_t size)
|
|
{
|
|
LogicalTape *lt;
|
|
long nblocks;
|
|
int newpos;
|
|
|
|
Assert(tapenum >= 0 && tapenum < lts->nTapes);
|
|
lt = <s->tapes[tapenum];
|
|
Assert(lt->frozen);
|
|
|
|
/*
|
|
* Easy case for seek within current block.
|
|
*/
|
|
if (size <= (size_t) lt->pos)
|
|
{
|
|
lt->pos -= (int) size;
|
|
return true;
|
|
}
|
|
|
|
/*
|
|
* Not-so-easy case. Figure out whether it's possible at all.
|
|
*/
|
|
size -= (size_t) lt->pos; /* part within this block */
|
|
nblocks = size / BLCKSZ;
|
|
size = size % BLCKSZ;
|
|
if (size)
|
|
{
|
|
nblocks++;
|
|
newpos = (int) (BLCKSZ - size);
|
|
}
|
|
else
|
|
newpos = 0;
|
|
if (nblocks > lt->curBlockNumber)
|
|
return false; /* a seek too far... */
|
|
|
|
/*
|
|
* OK, we need to back up nblocks blocks. This implementation would be
|
|
* pretty inefficient for long seeks, but we really aren't expecting that
|
|
* (a seek over one tuple is typical).
|
|
*/
|
|
while (nblocks-- > 0)
|
|
{
|
|
long datablocknum = ltsRecallPrevBlockNum(lts, lt->indirect);
|
|
|
|
if (datablocknum == -1L)
|
|
elog(ERROR, "unexpected end of tape");
|
|
lt->curBlockNumber--;
|
|
if (nblocks == 0)
|
|
{
|
|
ltsReadBlock(lts, datablocknum, (void *) lt->buffer);
|
|
lt->nbytes = BLCKSZ;
|
|
}
|
|
}
|
|
lt->pos = newpos;
|
|
return true;
|
|
}
|
|
|
|
/*
|
|
* Seek to an arbitrary position in a logical tape.
|
|
*
|
|
* *Only* a frozen-for-read tape can be seeked.
|
|
*
|
|
* Return value is TRUE if seek successful, FALSE if there isn't that much
|
|
* data in the tape (in which case there's no state change).
|
|
*/
|
|
bool
|
|
LogicalTapeSeek(LogicalTapeSet *lts, int tapenum,
|
|
long blocknum, int offset)
|
|
{
|
|
LogicalTape *lt;
|
|
|
|
Assert(tapenum >= 0 && tapenum < lts->nTapes);
|
|
lt = <s->tapes[tapenum];
|
|
Assert(lt->frozen);
|
|
Assert(offset >= 0 && offset <= BLCKSZ);
|
|
|
|
/*
|
|
* Easy case for seek within current block.
|
|
*/
|
|
if (blocknum == lt->curBlockNumber && offset <= lt->nbytes)
|
|
{
|
|
lt->pos = offset;
|
|
return true;
|
|
}
|
|
|
|
/*
|
|
* Not-so-easy case. Figure out whether it's possible at all.
|
|
*/
|
|
if (blocknum < 0 || blocknum > lt->numFullBlocks ||
|
|
(blocknum == lt->numFullBlocks && offset > lt->lastBlockBytes))
|
|
return false;
|
|
|
|
/*
|
|
* OK, advance or back up to the target block. This implementation would
|
|
* be pretty inefficient for long seeks, but we really aren't expecting
|
|
* that (a seek over one tuple is typical).
|
|
*/
|
|
while (lt->curBlockNumber > blocknum)
|
|
{
|
|
long datablocknum = ltsRecallPrevBlockNum(lts, lt->indirect);
|
|
|
|
if (datablocknum == -1L)
|
|
elog(ERROR, "unexpected end of tape");
|
|
if (--lt->curBlockNumber == blocknum)
|
|
ltsReadBlock(lts, datablocknum, (void *) lt->buffer);
|
|
}
|
|
while (lt->curBlockNumber < blocknum)
|
|
{
|
|
long datablocknum = ltsRecallNextBlockNum(lts, lt->indirect,
|
|
lt->frozen);
|
|
|
|
if (datablocknum == -1L)
|
|
elog(ERROR, "unexpected end of tape");
|
|
if (++lt->curBlockNumber == blocknum)
|
|
ltsReadBlock(lts, datablocknum, (void *) lt->buffer);
|
|
}
|
|
lt->nbytes = (lt->curBlockNumber < lt->numFullBlocks) ?
|
|
BLCKSZ : lt->lastBlockBytes;
|
|
lt->pos = offset;
|
|
return true;
|
|
}
|
|
|
|
/*
|
|
* Obtain current position in a form suitable for a later LogicalTapeSeek.
|
|
*
|
|
* NOTE: it'd be OK to do this during write phase with intention of using
|
|
* the position for a seek after freezing. Not clear if anyone needs that.
|
|
*/
|
|
void
|
|
LogicalTapeTell(LogicalTapeSet *lts, int tapenum,
|
|
long *blocknum, int *offset)
|
|
{
|
|
LogicalTape *lt;
|
|
|
|
Assert(tapenum >= 0 && tapenum < lts->nTapes);
|
|
lt = <s->tapes[tapenum];
|
|
*blocknum = lt->curBlockNumber;
|
|
*offset = lt->pos;
|
|
}
|
|
|
|
/*
|
|
* Obtain total disk space currently used by a LogicalTapeSet, in blocks.
|
|
*/
|
|
long
|
|
LogicalTapeSetBlocks(LogicalTapeSet *lts)
|
|
{
|
|
return lts->nFileBlocks;
|
|
}
|