diff options
Diffstat (limited to 'myisam')
| -rw-r--r-- | myisam/mi_dynrec.c | 157 |
1 files changed, 129 insertions, 28 deletions
diff --git a/myisam/mi_dynrec.c b/myisam/mi_dynrec.c index 0ffab05b6bc..c4865315283 100644 --- a/myisam/mi_dynrec.c +++ b/myisam/mi_dynrec.c @@ -1095,12 +1095,41 @@ void _my_store_blob_length(byte *pos,uint pack_length,uint length) } - /* Read record from datafile */ - /* Returns 0 if ok, -1 if error */ +/* + Read record from datafile. + + SYNOPSIS + _mi_read_dynamic_record() + info MI_INFO pointer to table. + filepos From where to read the record. + buf Destination for record. + + NOTE + + If a write buffer is active, it needs to be flushed if its contents + intersects with the record to read. We always check if the position + of the first byte of the write buffer is lower than the position + past the last byte to read. In theory this is also true if the write + buffer is completely below the read segment. That is, if there is no + intersection. But this case is unusual. We flush anyway. Only if the + first byte in the write buffer is above the last byte to read, we do + not flush. + + A dynamic record may need several reads. So this check must be done + before every read. Reading a dynamic record starts with reading the + block header. If the record does not fit into the free space of the + header, the block may be longer than the header. In this case a + second read is necessary. These one or two reads repeat for every + part of the record. + + RETURN + 0 OK + -1 Error +*/ int _mi_read_dynamic_record(MI_INFO *info, my_off_t filepos, byte *buf) { - int flag; + int block_of_record; uint b_type,left_length; byte *to; MI_BLOCK_INFO block_info; @@ -1112,17 +1141,16 @@ int _mi_read_dynamic_record(MI_INFO *info, my_off_t filepos, byte *buf) LINT_INIT(to); LINT_INIT(left_length); file=info->dfile; - block_info.next_filepos=filepos; /* for easyer loop */ - flag=block_info.second_read=0; + block_of_record= 0; /* First block of record is numbered as zero. */ + block_info.second_read= 0; do { if (info->opt_flag & WRITE_CACHE_USED && - info->rec_cache.pos_in_file <= block_info.next_filepos && + info->rec_cache.pos_in_file < filepos + MI_BLOCK_INFO_HEADER_LENGTH && flush_io_cache(&info->rec_cache)) goto err; info->rec_cache.seek_not_done=1; - if ((b_type=_mi_get_block_info(&block_info,file, - block_info.next_filepos)) + if ((b_type= _mi_get_block_info(&block_info, file, filepos)) & (BLOCK_DELETED | BLOCK_ERROR | BLOCK_SYNC_ERROR | BLOCK_FATAL_ERROR)) { @@ -1130,9 +1158,8 @@ int _mi_read_dynamic_record(MI_INFO *info, my_off_t filepos, byte *buf) my_errno=HA_ERR_RECORD_DELETED; goto err; } - if (flag == 0) /* First block */ + if (block_of_record++ == 0) /* First block */ { - flag=1; if (block_info.rec_len > (uint) info->s->base.max_pack_length) goto panic; if (info->s->base.blobs) @@ -1147,11 +1174,35 @@ int _mi_read_dynamic_record(MI_INFO *info, my_off_t filepos, byte *buf) } if (left_length < block_info.data_len || ! block_info.data_len) goto panic; /* Wrong linked record */ - if (my_pread(file,(byte*) to,block_info.data_len,block_info.filepos, - MYF(MY_NABP))) - goto panic; - left_length-=block_info.data_len; - to+=block_info.data_len; + /* copy information that is already read */ + { + uint offset= (uint) (block_info.filepos - filepos); + uint prefetch_len= (sizeof(block_info.header) - offset); + filepos+= sizeof(block_info.header); + + if (prefetch_len > block_info.data_len) + prefetch_len= block_info.data_len; + if (prefetch_len) + { + memcpy((byte*) to, block_info.header + offset, prefetch_len); + block_info.data_len-= prefetch_len; + left_length-= prefetch_len; + to+= prefetch_len; + } + } + /* read rest of record from file */ + if (block_info.data_len) + { + if (info->opt_flag & WRITE_CACHE_USED && + info->rec_cache.pos_in_file < filepos + block_info.data_len && + flush_io_cache(&info->rec_cache)) + goto err; + if (my_read(file, (byte*) to, block_info.data_len, MYF(MY_NABP))) + goto panic; + left_length-=block_info.data_len; + to+=block_info.data_len; + } + filepos= block_info.next_filepos; } while (left_length); info->update|= HA_STATE_AKTIV; /* We have a aktive record */ @@ -1308,11 +1359,45 @@ err: } +/* + Read record from datafile. + + SYNOPSIS + _mi_read_rnd_dynamic_record() + info MI_INFO pointer to table. + buf Destination for record. + filepos From where to read the record. + skip_deleted_blocks If to repeat reading until a non-deleted + record is found. + + NOTE + + If a write buffer is active, it needs to be flushed if its contents + intersects with the record to read. We always check if the position + of the first byte of the write buffer is lower than the position + past the last byte to read. In theory this is also true if the write + buffer is completely below the read segment. That is, if there is no + intersection. But this case is unusual. We flush anyway. Only if the + first byte in the write buffer is above the last byte to read, we do + not flush. + + A dynamic record may need several reads. So this check must be done + before every read. Reading a dynamic record starts with reading the + block header. If the record does not fit into the free space of the + header, the block may be longer than the header. In this case a + second read is necessary. These one or two reads repeat for every + part of the record. + + RETURN + 0 OK + != 0 Error +*/ + int _mi_read_rnd_dynamic_record(MI_INFO *info, byte *buf, register my_off_t filepos, - my_bool skipp_deleted_blocks) + my_bool skip_deleted_blocks) { - int flag,info_read,save_errno; + int block_of_record, info_read, save_errno; uint left_len,b_type; byte *to; MI_BLOCK_INFO block_info; @@ -1338,7 +1423,8 @@ int _mi_read_rnd_dynamic_record(MI_INFO *info, byte *buf, else info_read=1; /* memory-keyinfoblock is ok */ - flag=block_info.second_read=0; + block_of_record= 0; /* First block of record is numbered as zero. */ + block_info.second_read= 0; left_len=1; do { @@ -1361,15 +1447,15 @@ int _mi_read_rnd_dynamic_record(MI_INFO *info, byte *buf, { if (_mi_read_cache(&info->rec_cache,(byte*) block_info.header,filepos, sizeof(block_info.header), - (!flag && skipp_deleted_blocks ? READING_NEXT : 0) | - READING_HEADER)) + (!block_of_record && skip_deleted_blocks ? + READING_NEXT : 0) | READING_HEADER)) goto panic; b_type=_mi_get_block_info(&block_info,-1,filepos); } else { if (info->opt_flag & WRITE_CACHE_USED && - info->rec_cache.pos_in_file <= filepos && + info->rec_cache.pos_in_file < filepos + MI_BLOCK_INFO_HEADER_LENGTH && flush_io_cache(&info->rec_cache)) DBUG_RETURN(my_errno); info->rec_cache.seek_not_done=1; @@ -1380,7 +1466,7 @@ int _mi_read_rnd_dynamic_record(MI_INFO *info, byte *buf, BLOCK_FATAL_ERROR)) { if ((b_type & (BLOCK_DELETED | BLOCK_SYNC_ERROR)) - && skipp_deleted_blocks) + && skip_deleted_blocks) { filepos=block_info.filepos+block_info.block_len; block_info.second_read=0; @@ -1394,7 +1480,7 @@ int _mi_read_rnd_dynamic_record(MI_INFO *info, byte *buf, } goto err; } - if (flag == 0) /* First block */ + if (block_of_record == 0) /* First block */ { if (block_info.rec_len > (uint) share->base.max_pack_length) goto panic; @@ -1427,7 +1513,7 @@ int _mi_read_rnd_dynamic_record(MI_INFO *info, byte *buf, left_len-=tmp_length; to+=tmp_length; filepos+=tmp_length; - } + } } /* read rest of record from file */ if (block_info.data_len) @@ -1436,11 +1522,17 @@ int _mi_read_rnd_dynamic_record(MI_INFO *info, byte *buf, { if (_mi_read_cache(&info->rec_cache,(byte*) to,filepos, block_info.data_len, - (!flag && skipp_deleted_blocks) ? READING_NEXT :0)) + (!block_of_record && skip_deleted_blocks) ? + READING_NEXT : 0)) goto panic; } else { + if (info->opt_flag & WRITE_CACHE_USED && + info->rec_cache.pos_in_file < + block_info.filepos + block_info.data_len && + flush_io_cache(&info->rec_cache)) + goto err; /* VOID(my_seek(info->dfile,filepos,MY_SEEK_SET,MYF(0))); */ if (my_read(info->dfile,(byte*) to,block_info.data_len,MYF(MY_NABP))) { @@ -1450,10 +1542,14 @@ int _mi_read_rnd_dynamic_record(MI_INFO *info, byte *buf, } } } - if (flag++ == 0) + /* + Increment block-of-record counter. If it was the first block, + remember the position behind the block for the next call. + */ + if (block_of_record++ == 0) { - info->nextpos=block_info.filepos+block_info.block_len; - skipp_deleted_blocks=0; + info->nextpos= block_info.filepos + block_info.block_len; + skip_deleted_blocks= 0; } left_len-=block_info.data_len; to+=block_info.data_len; @@ -1485,6 +1581,11 @@ uint _mi_get_block_info(MI_BLOCK_INFO *info, File file, my_off_t filepos) if (file >= 0) { + /* + We do not use my_pread() here because we want to have the file + pointer set to the end of the header after this function. + my_pread() may leave the file pointer untouched. + */ VOID(my_seek(file,filepos,MY_SEEK_SET,MYF(0))); if (my_read(file,(char*) header,sizeof(info->header),MYF(0)) != sizeof(info->header)) |