diff --git a/mysys/mf_iocache.c b/mysys/mf_iocache.c index 620ac667a8b..b7fe36ac049 100644 --- a/mysys/mf_iocache.c +++ b/mysys/mf_iocache.c @@ -455,7 +455,9 @@ my_bool reinit_io_cache(IO_CACHE *info, enum cache_type type, RETURN 0 we succeeded in reading all data - 1 Error: can't read requested characters + 1 Error: couldn't read requested characters. In this case: + If info->error == -1, we got a read error. + Otherwise info->error contains the number of bytes in Buffer. */ int _my_b_read(register IO_CACHE *info, uchar *Buffer, size_t Count) @@ -464,6 +466,7 @@ int _my_b_read(register IO_CACHE *info, uchar *Buffer, size_t Count) my_off_t pos_in_file; DBUG_ENTER("_my_b_read"); + /* If the buffer is not empty yet, copy what is available. */ if ((left_length= (size_t) (info->read_end-info->read_pos))) { DBUG_ASSERT(Count >= left_length); /* User is not using my_b_read() */ @@ -475,7 +478,7 @@ int _my_b_read(register IO_CACHE *info, uchar *Buffer, size_t Count) /* pos_in_file always point on where info->buffer was read */ pos_in_file=info->pos_in_file+ (size_t) (info->read_end - info->buffer); - /* + /* Whenever a function which operates on IO_CACHE flushes/writes some part of the IO_CACHE to disk it will set the property "seek_not_done" to indicate this to other functions operating @@ -502,19 +505,38 @@ int _my_b_read(register IO_CACHE *info, uchar *Buffer, size_t Count) } } + /* + Calculate, how much we are within a IO_SIZE block. Ideally this + should be zero. + */ diff_length= (size_t) (pos_in_file & (IO_SIZE-1)); + + /* + If more than a block plus the rest of the current block is wanted, + we do read directly, without filling the buffer. + */ if (Count >= (size_t) (IO_SIZE+(IO_SIZE-diff_length))) { /* Fill first intern buffer */ size_t read_length; if (info->end_of_file <= pos_in_file) - { /* End of file */ + { + /* End of file. Return, what we did copy from the buffer. */ info->error= (int) left_length; DBUG_RETURN(1); } + /* + Crop the wanted count to a multiple of IO_SIZE and subtract, + what we did already read from a block. That way, the read will + end aligned with a block. + */ length=(Count & (size_t) ~(IO_SIZE-1))-diff_length; if ((read_length= my_read(info->file,Buffer, length, info->myflags)) != length) { + /* + If we didn't get, what we wanted, we either return -1 for a read + error, or (it's end of file), how much we got in total. + */ info->error= (read_length == (size_t) -1 ? -1 : (int) (read_length+left_length)); DBUG_RETURN(1); @@ -526,15 +548,27 @@ int _my_b_read(register IO_CACHE *info, uchar *Buffer, size_t Count) diff_length=0; } + /* + At this point, we want less than one and a partial block. + We will read a full cache, minus the number of bytes, we are + within a block already. So we will reach new alignment. + */ max_length= info->read_length-diff_length; + /* We will not read past end of file. */ if (info->type != READ_FIFO && max_length > (info->end_of_file - pos_in_file)) max_length= (size_t) (info->end_of_file - pos_in_file); + /* + If there is nothing left to read, + we either are done, or we failed to fulfill the request. + Otherwise, we read max_length into the cache. + */ if (!max_length) { if (Count) { - info->error= left_length; /* We only got this many char */ + /* We couldn't fulfil the request. Return, how much we got. */ + info->error= left_length; DBUG_RETURN(1); } length=0; /* Didn't read any chars */ @@ -543,13 +577,23 @@ int _my_b_read(register IO_CACHE *info, uchar *Buffer, size_t Count) info->myflags)) < Count || length == (size_t) -1) { + /* + We got an read error, or less than requested (end of file). + If not a read error, copy, what we got. + */ if (length != (size_t) -1) memcpy(Buffer, info->buffer, length); info->pos_in_file= pos_in_file; + /* For a read error, return -1, otherwise, what we got in total. */ info->error= length == (size_t) -1 ? -1 : (int) (length+left_length); info->read_pos=info->read_end=info->buffer; DBUG_RETURN(1); } + /* + Count is the remaining number of bytes requested. + length is the amount of data in the cache. + Read Count bytes from the cache. + */ info->read_pos=info->buffer+Count; info->read_end=info->buffer+length; info->pos_in_file=pos_in_file; diff --git a/sql/sql_base.cc b/sql/sql_base.cc index 3758ec7253d..d69a5b1aa77 100644 --- a/sql/sql_base.cc +++ b/sql/sql_base.cc @@ -1931,7 +1931,6 @@ TABLE_LIST *find_table_in_list(TABLE_LIST *table, } - /** Test that table is unique (It's only exists once in the table list) @@ -2054,6 +2053,11 @@ next: or (in case of MyISAMMRG) one of its children are not used later in the query. + For MyISAMMRG tables, it is assumed that all the underlying + tables of @c table (if any) are listed right after it and that + their @c parent_l field points at the main table. + + @retval non-NULL The table list element for the table that represents the duplicate. @retval NULL No duplicates found. diff --git a/storage/myisam/mi_statrec.c b/storage/myisam/mi_statrec.c index 74fca5902f5..7d595916d78 100644 --- a/storage/myisam/mi_statrec.c +++ b/storage/myisam/mi_statrec.c @@ -273,7 +273,12 @@ int _mi_read_rnd_static_record(MI_INFO *info, uchar *buf, DBUG_RETURN(error); } - /* Read record with cacheing */ + /* + Read record with caching. If my_b_read() returns TRUE, less than the + requested bytes have been read. In this case rec_cache.error is + either -1 for a read error, or contains the number of bytes copied + into the buffer. + */ error=my_b_read(&info->rec_cache,(uchar*) buf,share->base.reclength); if (info->s->base.pack_reclength != info->s->base.reclength && !error) {