fileset.c

Go to the documentation of this file.

/*-------------------------------------------------------------------------
 *
 * fileset.c
 *    Management of named temporary files.
 *
 * Portions Copyright (c) 1996-2025, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 * IDENTIFICATION
 *    src/backend/storage/file/fileset.c
 *
 * FileSets provide a temporary namespace (think directory) so that files can
 * be discovered by name.
 *
 * FileSets can be used by backends when the temporary files need to be
 * opened/closed multiple times and the underlying files need to survive across
 * transactions.
 *
 *-------------------------------------------------------------------------
 */
 
#include "postgres.h"
 
#include <limits.h>
 
#include "commands/tablespace.h"
#include "common/file_utils.h"
#include "common/hashfn.h"
#include "miscadmin.h"
#include "storage/fileset.h"
 
static void FileSetPath(char *path, FileSet *fileset, Oid tablespace);
static void FilePath(char *path, FileSet *fileset, const char *name);
static Oid  ChooseTablespace(const FileSet *fileset, const char *name);
 
/*
 * Initialize a space for temporary files. This API can be used by shared
 * fileset as well as if the temporary files are used only by single backend
 * but the files need to be opened and closed multiple times and also the
 * underlying files need to survive across transactions.
 *
 * The callers are expected to explicitly remove such files by using
 * FileSetDelete/FileSetDeleteAll.
 *
 * Files will be distributed over the tablespaces configured in
 * temp_tablespaces.
 *
 * Under the covers the set is one or more directories which will eventually
 * be deleted.
 */
void
FileSetInit(FileSet *fileset)
{
    static uint32 counter = 0;
 
    fileset->creator_pid = MyProcPid;
    fileset->number = counter;
    counter = (counter + 1) % INT_MAX;
 
    /* Capture the tablespace OIDs so that all backends agree on them. */
    PrepareTempTablespaces();
    fileset->ntablespaces =
        GetTempTablespaces(&fileset->tablespaces[0],
                           lengthof(fileset->tablespaces));
    if (fileset->ntablespaces == 0)
    {
        /* If the GUC is empty, use current database's default tablespace */
        fileset->tablespaces[0] = MyDatabaseTableSpace;
        fileset->ntablespaces = 1;
    }
    else
    {
        int         i;
 
        /*
         * An entry of InvalidOid means use the default tablespace for the
         * current database.  Replace that now, to be sure that all users of
         * the FileSet agree on what to do.
         */
        for (i = 0; i < fileset->ntablespaces; i++)
        {
            if (fileset->tablespaces[i] == InvalidOid)
                fileset->tablespaces[i] = MyDatabaseTableSpace;
        }
    }
}
 
/*
 * Create a new file in the given set.
 */
File
FileSetCreate(FileSet *fileset, const char *name)
{
    char        path[MAXPGPATH];
    File        file;
 
    FilePath(path, fileset, name);
    file = PathNameCreateTemporaryFile(path, false);
 
    /* If we failed, see if we need to create the directory on demand. */
    if (file <= 0)
    {
        char        tempdirpath[MAXPGPATH];
        char        filesetpath[MAXPGPATH];
        Oid         tablespace = ChooseTablespace(fileset, name);
 
        TempTablespacePath(tempdirpath, tablespace);
        FileSetPath(filesetpath, fileset, tablespace);
        PathNameCreateTemporaryDir(tempdirpath, filesetpath);
        file = PathNameCreateTemporaryFile(path, true);
    }
 
    return file;
}
 
/*
 * Open a file that was created with FileSetCreate()
 */
File
FileSetOpen(FileSet *fileset, const char *name, int mode)
{
    char        path[MAXPGPATH];
    File        file;
 
    FilePath(path, fileset, name);
    file = PathNameOpenTemporaryFile(path, mode);
 
    return file;
}
 
/*
 * Delete a file that was created with FileSetCreate().
 *
 * Return true if the file existed, false if didn't.
 */
bool
FileSetDelete(FileSet *fileset, const char *name,
              bool error_on_failure)
{
    char        path[MAXPGPATH];
 
    FilePath(path, fileset, name);
 
    return PathNameDeleteTemporaryFile(path, error_on_failure);
}
 
/*
 * Delete all files in the set.
 */
void
FileSetDeleteAll(FileSet *fileset)
{
    char        dirpath[MAXPGPATH];
    int         i;
 
    /*
     * Delete the directory we created in each tablespace.  Doesn't fail
     * because we use this in error cleanup paths, but can generate LOG
     * message on IO error.
     */
    for (i = 0; i < fileset->ntablespaces; ++i)
    {
        FileSetPath(dirpath, fileset, fileset->tablespaces[i]);
        PathNameDeleteTemporaryDir(dirpath);
    }
}
 
/*
 * Build the path for the directory holding the files backing a FileSet in a
 * given tablespace.
 */
static void
FileSetPath(char *path, FileSet *fileset, Oid tablespace)
{
    char        tempdirpath[MAXPGPATH];
 
    TempTablespacePath(tempdirpath, tablespace);
    snprintf(path, MAXPGPATH, "%s/%s%lu.%u.fileset",
             tempdirpath, PG_TEMP_FILE_PREFIX,
             (unsigned long) fileset->creator_pid, fileset->number);
}
 
/*
 * Sorting has to determine which tablespace a given temporary file belongs in.
 */
static Oid
ChooseTablespace(const FileSet *fileset, const char *name)
{
    uint32      hash = hash_bytes((const unsigned char *) name, strlen(name));
 
    return fileset->tablespaces[hash % fileset->ntablespaces];
}
 
/*
 * Compute the full path of a file in a FileSet.
 */
static void
FilePath(char *path, FileSet *fileset, const char *name)
{
    char        dirpath[MAXPGPATH];
 
    FileSetPath(dirpath, fileset, ChooseTablespace(fileset, name));
    snprintf(path, MAXPGPATH, "%s/%s", dirpath, name);
}