PostgreSQL 启动时会自动清理temporary-files directory

在使用数据库时，跑某些SQL的时候，如果work_mem内存不足会涉及一些临时空间的使用，比如排序，聚合，group by。
如果数据库突然crash了，或者某些原因未清除temp file。
数据库在重启的时候，会自动清理。

PostmasterMain(int argc, char *argv[])
  call
RemovePgTempFiles(void)
  call
RemovePgTempFilesInDir(const char *tmpdirname)

代码如下：
src/backend/storage/file/fd.c

/* Process one pgsql_tmp directory for RemovePgTempFiles */
static void
RemovePgTempFilesInDir(const char *tmpdirname)
{
    DIR        *temp_dir;
    struct dirent *temp_de;
    char        rm_path[MAXPGPATH];

    temp_dir = AllocateDir(tmpdirname);
    if (temp_dir == NULL)
    {
        /* anything except ENOENT is fishy */
        if (errno != ENOENT)
            elog(LOG,
                 "could not open temporary-files directory \"%s\": %m",
                 tmpdirname);
        return;
    }

    while ((temp_de = ReadDir(temp_dir, tmpdirname)) != NULL)
    {
        if (strcmp(temp_de->d_name, ".") == 0 ||
            strcmp(temp_de->d_name, "..") == 0)
            continue;

        snprintf(rm_path, sizeof(rm_path), "%s/%s",
                 tmpdirname, temp_de->d_name);

        if (strncmp(temp_de->d_name,
                    PG_TEMP_FILE_PREFIX,
                    strlen(PG_TEMP_FILE_PREFIX)) == 0)
            unlink(rm_path);    /* note we ignore any error */
        else
            elog(LOG,
                 "unexpected file found in temporary-files directory: \"%s\"",
                 rm_path);
    }

    FreeDir(temp_dir);
}