[postgresql] / src / backend / storage / file / buffile.c

/*-------------------------------------------------------------------------
 *
 * buffile.c
 *        Management of large buffered temporary files.
 *
 * Portions Copyright (c) 1996-2018, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 * IDENTIFICATION
 *        src/backend/storage/file/buffile.c
 *
 * NOTES:
 *
 * BufFiles provide a very incomplete emulation of stdio atop virtual Files
 * (as managed by fd.c).  Currently, we only support the buffered-I/O
 * aspect of stdio: a read or write of the low-level File occurs only
 * when the buffer is filled or emptied.  This is an even bigger win
 * for virtual Files than for ordinary kernel files, since reducing the
 * frequency with which a virtual File is touched reduces "thrashing"
 * of opening/closing file descriptors.
 *
 * Note that BufFile structs are allocated with palloc(), and therefore
 * will go away automatically at query/transaction end.  Since the underlying
 * virtual Files are made with OpenTemporaryFile, all resources for
 * the file are certain to be cleaned up even if processing is aborted
 * by ereport(ERROR).  The data structures required are made in the
 * palloc context that was current when the BufFile was created, and
 * any external resources such as temp files are owned by the ResourceOwner
 * that was current at that time.
 *
 * BufFile also supports temporary files that exceed the OS file size limit
 * (by opening multiple fd.c temporary files).  This is an essential feature
 * for sorts and hashjoins on large amounts of data.
 *
 * BufFile supports temporary files that can be made read-only and shared with
 * other backends, as infrastructure for parallel execution.  Such files need
 * to be created as a member of a SharedFileSet that all participants are
 * attached to.
 *-------------------------------------------------------------------------
 */

#include "postgres.h"

#include "executor/instrument.h"
#include "miscadmin.h"
#include "pgstat.h"
#include "storage/fd.h"
#include "storage/buffile.h"
#include "storage/buf_internals.h"
#include "utils/resowner.h"

/*
 * We break BufFiles into gigabyte-sized segments, regardless of RELSEG_SIZE.
 * The reason is that we'd like large BufFiles to be spread across multiple
 * tablespaces when available.
 */
#define MAX_PHYSICAL_FILESIZE   0x40000000
#define BUFFILE_SEG_SIZE                (MAX_PHYSICAL_FILESIZE / BLCKSZ)

/*
 * This data structure represents a buffered file that consists of one or
 * more physical files (each accessed through a virtual file descriptor
 * managed by fd.c).
 */
struct BufFile
{
        int                     numFiles;               /* number of physical files in set */
        /* all files except the last have length exactly MAX_PHYSICAL_FILESIZE */
        File       *files;                      /* palloc'd array with numFiles entries */
        off_t      *offsets;            /* palloc'd array with numFiles entries */

        /*
         * offsets[i] is the current seek position of files[i].  We use this to
         * avoid making redundant FileSeek calls.
         */

        bool            isInterXact;    /* keep open over transactions? */
        bool            dirty;                  /* does buffer need to be written? */
        bool            readOnly;               /* has the file been set to read only? */

        SharedFileSet *fileset;         /* space for segment files if shared */
        const char *name;                       /* name of this BufFile if shared */

        /*
         * resowner is the ResourceOwner to use for underlying temp files.  (We
         * don't need to remember the memory context we're using explicitly,
         * because after creation we only repalloc our arrays larger.)
         */
        ResourceOwner resowner;

        /*
         * "current pos" is position of start of buffer within the logical file.
         * Position as seen by user of BufFile is (curFile, curOffset + pos).
         */
        int                     curFile;                /* file index (0..n) part of current pos */
        off_t           curOffset;              /* offset part of current pos */
        int                     pos;                    /* next read/write position in buffer */
        int                     nbytes;                 /* total # of valid bytes in buffer */
        char            buffer[BLCKSZ];
};

static BufFile *makeBufFileCommon(int nfiles);
static BufFile *makeBufFile(File firstfile);
static void extendBufFile(BufFile *file);
static void BufFileLoadBuffer(BufFile *file);
static void BufFileDumpBuffer(BufFile *file);
static int      BufFileFlush(BufFile *file);
static File MakeNewSharedSegment(BufFile *file, int segment);

/*
 * Create BufFile and perform the common initialization.
 */
static BufFile *
makeBufFileCommon(int nfiles)
{
        BufFile    *file = (BufFile *) palloc(sizeof(BufFile));

        file->numFiles = nfiles;
        file->offsets = (off_t *) palloc0(sizeof(off_t) * nfiles);
        file->isInterXact = false;
        file->dirty = false;
        file->resowner = CurrentResourceOwner;
        file->curFile = 0;
        file->curOffset = 0L;
        file->pos = 0;
        file->nbytes = 0;

        return file;
}

/*
 * Create a BufFile given the first underlying physical file.
 * NOTE: caller must set isInterXact if appropriate.
 */
static BufFile *
makeBufFile(File firstfile)
{
        BufFile    *file = makeBufFileCommon(1);

        file->files = (File *) palloc(sizeof(File));
        file->files[0] = firstfile;
        file->readOnly = false;
        file->fileset = NULL;
        file->name = NULL;

        return file;
}

/*
 * Add another component temp file.
 */
static void
extendBufFile(BufFile *file)
{
        File            pfile;
        ResourceOwner oldowner;

        /* Be sure to associate the file with the BufFile's resource owner */
        oldowner = CurrentResourceOwner;
        CurrentResourceOwner = file->resowner;

        if (file->fileset == NULL)
                pfile = OpenTemporaryFile(file->isInterXact);
        else
                pfile = MakeNewSharedSegment(file, file->numFiles);

        Assert(pfile >= 0);

        CurrentResourceOwner = oldowner;

        file->files = (File *) repalloc(file->files,
                                                                        (file->numFiles + 1) * sizeof(File));
        file->offsets = (off_t *) repalloc(file->offsets,
                                                                           (file->numFiles + 1) * sizeof(off_t));
        file->files[file->numFiles] = pfile;
        file->offsets[file->numFiles] = 0L;
        file->numFiles++;
}

/*
 * Create a BufFile for a new temporary file (which will expand to become
 * multiple temporary files if more than MAX_PHYSICAL_FILESIZE bytes are
 * written to it).
 *
 * If interXact is true, the temp file will not be automatically deleted
 * at end of transaction.
 *
 * Note: if interXact is true, the caller had better be calling us in a
 * memory context, and with a resource owner, that will survive across
 * transaction boundaries.
 */
BufFile *
BufFileCreateTemp(bool interXact)
{
        BufFile    *file;
        File            pfile;

        pfile = OpenTemporaryFile(interXact);
        Assert(pfile >= 0);

        file = makeBufFile(pfile);
        file->isInterXact = interXact;

        return file;
}

/*
 * Build the name for a given segment of a given BufFile.
 */
static void
SharedSegmentName(char *name, const char *buffile_name, int segment)
{
        snprintf(name, MAXPGPATH, "%s.%d", buffile_name, segment);
}

/*
 * Create a new segment file backing a shared BufFile.
 */
static File
MakeNewSharedSegment(BufFile *buffile, int segment)
{
        char            name[MAXPGPATH];
        File            file;

        /*
         * It is possible that there are files left over from before a crash
         * restart with the same name.  In order for BufFileOpenShared() not to
         * get confused about how many segments there are, we'll unlink the next
         * segment number if it already exists.
         */
        SharedSegmentName(name, buffile->name, segment + 1);
        SharedFileSetDelete(buffile->fileset, name, true);

        /* Create the new segment. */
        SharedSegmentName(name, buffile->name, segment);
        file = SharedFileSetCreate(buffile->fileset, name);

        /* SharedFileSetCreate would've errored out */
        Assert(file > 0);

        return file;
}

/*
 * Create a BufFile that can be discovered and opened read-only by other
 * backends that are attached to the same SharedFileSet using the same name.
 *
 * The naming scheme for shared BufFiles is left up to the calling code.  The
 * name will appear as part of one or more filenames on disk, and might
 * provide clues to administrators about which subsystem is generating
 * temporary file data.  Since each SharedFileSet object is backed by one or
 * more uniquely named temporary directory, names don't conflict with
 * unrelated SharedFileSet objects.
 */
BufFile *
BufFileCreateShared(SharedFileSet *fileset, const char *name)
{
        BufFile    *file;

        file = makeBufFileCommon(1);
        file->fileset = fileset;
        file->name = pstrdup(name);
        file->files = (File *) palloc(sizeof(File));
        file->files[0] = MakeNewSharedSegment(file, 0);
        file->readOnly = false;

        return file;
}

/*
 * Open a file that was previously created in another backend (or this one)
 * with BufFileCreateShared in the same SharedFileSet using the same name.
 * The backend that created the file must have called BufFileClose() or
 * BufFileExportShared() to make sure that it is ready to be opened by other
 * backends and render it read-only.
 */
BufFile *
BufFileOpenShared(SharedFileSet *fileset, const char *name)
{
        BufFile    *file;
        char            segment_name[MAXPGPATH];
        Size            capacity = 16;
        File       *files;
        int                     nfiles = 0;

        files = palloc(sizeof(File) * capacity);

        /*
         * We don't know how many segments there are, so we'll probe the
         * filesystem to find out.
         */
        for (;;)
        {
                /* See if we need to expand our file segment array. */
                if (nfiles + 1 > capacity)
                {
                        capacity *= 2;
                        files = repalloc(files, sizeof(File) * capacity);
                }
                /* Try to load a segment. */
                SharedSegmentName(segment_name, name, nfiles);
                files[nfiles] = SharedFileSetOpen(fileset, segment_name);
                if (files[nfiles] <= 0)
                        break;
                ++nfiles;

                CHECK_FOR_INTERRUPTS();
        }

        /*
         * If we didn't find any files at all, then no BufFile exists with this
         * name.
         */
        if (nfiles == 0)
                ereport(ERROR,
                                (errcode_for_file_access(),
                                 errmsg("could not open BufFile \"%s\"", name)));

        file = makeBufFileCommon(nfiles);
        file->files = files;
        file->readOnly = true;          /* Can't write to files opened this way */
        file->fileset = fileset;
        file->name = pstrdup(name);

        return file;
}

/*
 * Delete a BufFile that was created by BufFileCreateShared in the given
 * SharedFileSet using the given name.
 *
 * It is not necessary to delete files explicitly with this function.  It is
 * provided only as a way to delete files proactively, rather than waiting for
 * the SharedFileSet to be cleaned up.
 *
 * Only one backend should attempt to delete a given name, and should know
 * that it exists and has been exported or closed.
 */
void
BufFileDeleteShared(SharedFileSet *fileset, const char *name)
{
        char            segment_name[MAXPGPATH];
        int                     segment = 0;
        bool            found = false;

        /*
         * We don't know how many segments the file has.  We'll keep deleting
         * until we run out.  If we don't manage to find even an initial segment,
         * raise an error.
         */
        for (;;)
        {
                SharedSegmentName(segment_name, name, segment);
                if (!SharedFileSetDelete(fileset, segment_name, true))
                        break;
                found = true;
                ++segment;

                CHECK_FOR_INTERRUPTS();
        }

        if (!found)
                elog(ERROR, "could not delete unknown shared BufFile \"%s\"", name);
}

/*
 * BufFileExportShared --- flush and make read-only, in preparation for sharing.
 */
void
BufFileExportShared(BufFile *file)
{
        /* Must be a file belonging to a SharedFileSet. */
        Assert(file->fileset != NULL);

        /* It's probably a bug if someone calls this twice. */
        Assert(!file->readOnly);

        BufFileFlush(file);
        file->readOnly = true;
}

/*
 * Close a BufFile
 *
 * Like fclose(), this also implicitly FileCloses the underlying File.
 */
void
BufFileClose(BufFile *file)
{
        int                     i;

        /* flush any unwritten data */
        BufFileFlush(file);
        /* close and delete the underlying file(s) */
        for (i = 0; i < file->numFiles; i++)
                FileClose(file->files[i]);
        /* release the buffer space */
        pfree(file->files);
        pfree(file->offsets);
        pfree(file);
}

/*
 * BufFileLoadBuffer
 *
 * Load some data into buffer, if possible, starting from curOffset.
 * At call, must have dirty = false, pos and nbytes = 0.
 * On exit, nbytes is number of bytes loaded.
 */
static void
BufFileLoadBuffer(BufFile *file)
{
        File            thisfile;

        /*
         * Advance to next component file if necessary and possible.
         */
        if (file->curOffset >= MAX_PHYSICAL_FILESIZE &&
                file->curFile + 1 < file->numFiles)
        {
                file->curFile++;
                file->curOffset = 0L;
        }

        /*
         * May need to reposition physical file.
         */
        thisfile = file->files[file->curFile];
        if (file->curOffset != file->offsets[file->curFile])
        {
                if (FileSeek(thisfile, file->curOffset, SEEK_SET) != file->curOffset)
                        return;                         /* seek failed, read nothing */
                file->offsets[file->curFile] = file->curOffset;
        }

        /*
         * Read whatever we can get, up to a full bufferload.
         */
        file->nbytes = FileRead(thisfile,
                                                        file->buffer,
                                                        sizeof(file->buffer),
                                                        WAIT_EVENT_BUFFILE_READ);
        if (file->nbytes < 0)
                file->nbytes = 0;
        file->offsets[file->curFile] += file->nbytes;
        /* we choose not to advance curOffset here */

        if (file->nbytes > 0)
                pgBufferUsage.temp_blks_read++;
}

/*
 * BufFileDumpBuffer
 *
 * Dump buffer contents starting at curOffset.
 * At call, should have dirty = true, nbytes > 0.
 * On exit, dirty is cleared if successful write, and curOffset is advanced.
 */
static void
BufFileDumpBuffer(BufFile *file)
{
        int                     wpos = 0;
        int                     bytestowrite;
        File            thisfile;

        /*
         * Unlike BufFileLoadBuffer, we must dump the whole buffer even if it
         * crosses a component-file boundary; so we need a loop.
         */
        while (wpos < file->nbytes)
        {
                off_t           availbytes;

                /*
                 * Advance to next component file if necessary and possible.
                 */
                if (file->curOffset >= MAX_PHYSICAL_FILESIZE)
                {
                        while (file->curFile + 1 >= file->numFiles)
                                extendBufFile(file);
                        file->curFile++;
                        file->curOffset = 0L;
                }

                /*
                 * Determine how much we need to write into this file.
                 */
                bytestowrite = file->nbytes - wpos;
                availbytes = MAX_PHYSICAL_FILESIZE - file->curOffset;

                if ((off_t) bytestowrite > availbytes)
                        bytestowrite = (int) availbytes;

                /*
                 * May need to reposition physical file.
                 */
                thisfile = file->files[file->curFile];
                if (file->curOffset != file->offsets[file->curFile])
                {
                        if (FileSeek(thisfile, file->curOffset, SEEK_SET) != file->curOffset)
                                return;                 /* seek failed, give up */
                        file->offsets[file->curFile] = file->curOffset;
                }
                bytestowrite = FileWrite(thisfile,
                                                                 file->buffer + wpos,
                                                                 bytestowrite,
                                                                 WAIT_EVENT_BUFFILE_WRITE);
                if (bytestowrite <= 0)
                        return;                         /* failed to write */
                file->offsets[file->curFile] += bytestowrite;
                file->curOffset += bytestowrite;
                wpos += bytestowrite;

                pgBufferUsage.temp_blks_written++;
        }
        file->dirty = false;

        /*
         * At this point, curOffset has been advanced to the end of the buffer,
         * ie, its original value + nbytes.  We need to make it point to the
         * logical file position, ie, original value + pos, in case that is less
         * (as could happen due to a small backwards seek in a dirty buffer!)
         */
        file->curOffset -= (file->nbytes - file->pos);
        if (file->curOffset < 0)        /* handle possible segment crossing */
        {
                file->curFile--;
                Assert(file->curFile >= 0);
                file->curOffset += MAX_PHYSICAL_FILESIZE;
        }

        /*
         * Now we can set the buffer empty without changing the logical position
         */
        file->pos = 0;
        file->nbytes = 0;
}

/*
 * BufFileRead
 *
 * Like fread() except we assume 1-byte element size.
 */
size_t
BufFileRead(BufFile *file, void *ptr, size_t size)
{
        size_t          nread = 0;
        size_t          nthistime;

        if (file->dirty)
        {
                if (BufFileFlush(file) != 0)
                        return 0;                       /* could not flush... */
                Assert(!file->dirty);
        }

        while (size > 0)
        {
                if (file->pos >= file->nbytes)
                {
                        /* Try to load more data into buffer. */
                        file->curOffset += file->pos;
                        file->pos = 0;
                        file->nbytes = 0;
                        BufFileLoadBuffer(file);
                        if (file->nbytes <= 0)
                                break;                  /* no more data available */
                }

                nthistime = file->nbytes - file->pos;
                if (nthistime > size)
                        nthistime = size;
                Assert(nthistime > 0);

                memcpy(ptr, file->buffer + file->pos, nthistime);

                file->pos += nthistime;
                ptr = (void *) ((char *) ptr + nthistime);
                size -= nthistime;
                nread += nthistime;
        }

        return nread;
}

/*
 * BufFileWrite
 *
 * Like fwrite() except we assume 1-byte element size.
 */
size_t
BufFileWrite(BufFile *file, void *ptr, size_t size)
{
        size_t          nwritten = 0;
        size_t          nthistime;

        Assert(!file->readOnly);

        while (size > 0)
        {
                if (file->pos >= BLCKSZ)
                {
                        /* Buffer full, dump it out */
                        if (file->dirty)
                        {
                                BufFileDumpBuffer(file);
                                if (file->dirty)
                                        break;          /* I/O error */
                        }
                        else
                        {
                                /* Hmm, went directly from reading to writing? */
                                file->curOffset += file->pos;
                                file->pos = 0;
                                file->nbytes = 0;
                        }
                }

                nthistime = BLCKSZ - file->pos;
                if (nthistime > size)
                        nthistime = size;
                Assert(nthistime > 0);

                memcpy(file->buffer + file->pos, ptr, nthistime);

                file->dirty = true;
                file->pos += nthistime;
                if (file->nbytes < file->pos)
                        file->nbytes = file->pos;
                ptr = (void *) ((char *) ptr + nthistime);
                size -= nthistime;
                nwritten += nthistime;
        }

        return nwritten;
}

/*
 * BufFileFlush
 *
 * Like fflush()
 */
static int
BufFileFlush(BufFile *file)
{
        if (file->dirty)
        {
                BufFileDumpBuffer(file);
                if (file->dirty)
                        return EOF;
        }

        return 0;
}

/*
 * BufFileSeek
 *
 * Like fseek(), except that target position needs two values in order to
 * work when logical filesize exceeds maximum value representable by off_t.
 * We do not support relative seeks across more than that, however.
 *
 * Result is 0 if OK, EOF if not.  Logical position is not moved if an
 * impossible seek is attempted.
 */
int
BufFileSeek(BufFile *file, int fileno, off_t offset, int whence)
{
        int                     newFile;
        off_t           newOffset;

        switch (whence)
        {
                case SEEK_SET:
                        if (fileno < 0)
                                return EOF;
                        newFile = fileno;
                        newOffset = offset;
                        break;
                case SEEK_CUR:

                        /*
                         * Relative seek considers only the signed offset, ignoring
                         * fileno. Note that large offsets (> 1 gig) risk overflow in this
                         * add, unless we have 64-bit off_t.
                         */
                        newFile = file->curFile;
                        newOffset = (file->curOffset + file->pos) + offset;
                        break;
#ifdef NOT_USED
                case SEEK_END:
                        /* could be implemented, not needed currently */
                        break;
#endif
                default:
                        elog(ERROR, "invalid whence: %d", whence);
                        return EOF;
        }
        while (newOffset < 0)
        {
                if (--newFile < 0)
                        return EOF;
                newOffset += MAX_PHYSICAL_FILESIZE;
        }
        if (newFile == file->curFile &&
                newOffset >= file->curOffset &&
                newOffset <= file->curOffset + file->nbytes)
        {
                /*
                 * Seek is to a point within existing buffer; we can just adjust
                 * pos-within-buffer, without flushing buffer.  Note this is OK
                 * whether reading or writing, but buffer remains dirty if we were
                 * writing.
                 */
                file->pos = (int) (newOffset - file->curOffset);
                return 0;
        }
        /* Otherwise, must reposition buffer, so flush any dirty data */
        if (BufFileFlush(file) != 0)
                return EOF;

        /*
         * At this point and no sooner, check for seek past last segment. The
         * above flush could have created a new segment, so checking sooner would
         * not work (at least not with this code).
         */

        /* convert seek to "start of next seg" to "end of last seg" */
        if (newFile == file->numFiles && newOffset == 0)
        {
                newFile--;
                newOffset = MAX_PHYSICAL_FILESIZE;
        }
        while (newOffset > MAX_PHYSICAL_FILESIZE)
        {
                if (++newFile >= file->numFiles)
                        return EOF;
                newOffset -= MAX_PHYSICAL_FILESIZE;
        }
        if (newFile >= file->numFiles)
                return EOF;
        /* Seek is OK! */
        file->curFile = newFile;
        file->curOffset = newOffset;
        file->pos = 0;
        file->nbytes = 0;
        return 0;
}

void
BufFileTell(BufFile *file, int *fileno, off_t *offset)
{
        *fileno = file->curFile;
        *offset = file->curOffset + file->pos;
}

/*
 * BufFileSeekBlock --- block-oriented seek
 *
 * Performs absolute seek to the start of the n'th BLCKSZ-sized block of
 * the file.  Note that users of this interface will fail if their files
 * exceed BLCKSZ * LONG_MAX bytes, but that is quite a lot; we don't work
 * with tables bigger than that, either...
 *
 * Result is 0 if OK, EOF if not.  Logical position is not moved if an
 * impossible seek is attempted.
 */
int
BufFileSeekBlock(BufFile *file, long blknum)
{
        return BufFileSeek(file,
                                           (int) (blknum / BUFFILE_SEG_SIZE),
                                           (off_t) (blknum % BUFFILE_SEG_SIZE) * BLCKSZ,
                                           SEEK_SET);
}

#ifdef NOT_USED
/*
 * BufFileTellBlock --- block-oriented tell
 *
 * Any fractional part of a block in the current seek position is ignored.
 */
long
BufFileTellBlock(BufFile *file)
{
        long            blknum;

        blknum = (file->curOffset + file->pos) / BLCKSZ;
        blknum += file->curFile * BUFFILE_SEG_SIZE;
        return blknum;
}

#endif

/*
 * Return the current file size.
 *
 * Counts any holes left behind by BufFileAppend as part of the size.
 * Returns -1 on error.
 */
off_t
BufFileSize(BufFile *file)
{
        off_t           lastFileSize;

        /* Get the size of the last physical file by seeking to end. */
        lastFileSize = FileSeek(file->files[file->numFiles - 1], 0, SEEK_END);
        if (lastFileSize < 0)
                return -1;
        file->offsets[file->numFiles - 1] = lastFileSize;

        return ((file->numFiles - 1) * (off_t) MAX_PHYSICAL_FILESIZE) +
                lastFileSize;
}

/*
 * Append the contents of source file (managed within shared fileset) to
 * end of target file (managed within same shared fileset).
 *
 * Note that operation subsumes ownership of underlying resources from
 * "source".  Caller should never call BufFileClose against source having
 * called here first.  Resource owners for source and target must match,
 * too.
 *
 * This operation works by manipulating lists of segment files, so the
 * file content is always appended at a MAX_PHYSICAL_FILESIZE-aligned
 * boundary, typically creating empty holes before the boundary.  These
 * areas do not contain any interesting data, and cannot be read from by
 * caller.
 *
 * Returns the block number within target where the contents of source
 * begins.  Caller should apply this as an offset when working off block
 * positions that are in terms of the original BufFile space.
 */
long
BufFileAppend(BufFile *target, BufFile *source)
{
        long            startBlock = target->numFiles * BUFFILE_SEG_SIZE;
        int                     newNumFiles = target->numFiles + source->numFiles;
        int                     i;

        Assert(target->fileset != NULL);
        Assert(source->readOnly);
        Assert(!source->dirty);
        Assert(source->fileset != NULL);

        if (target->resowner != source->resowner)
                elog(ERROR, "could not append BufFile with non-matching resource owner");

        target->files = (File *)
                repalloc(target->files, sizeof(File) * newNumFiles);
        target->offsets = (off_t *)
                repalloc(target->offsets, sizeof(off_t) * newNumFiles);
        for (i = target->numFiles; i < newNumFiles; i++)
        {
                target->files[i] = source->files[i - target->numFiles];
                target->offsets[i] = source->offsets[i - target->numFiles];
        }
        target->numFiles = newNumFiles;

        return startBlock;
}