diff options
Diffstat (limited to 'sql/sql_update.cc')
| -rw-r--r-- | sql/sql_update.cc | 93 |
1 files changed, 62 insertions, 31 deletions
diff --git a/sql/sql_update.cc b/sql/sql_update.cc index 7da8a68546f..01c70a7a268 100644 --- a/sql/sql_update.cc +++ b/sql/sql_update.cc @@ -25,11 +25,68 @@ #include "sql_trigger.h" #include "debug_sync.h" -/* Return 0 if row hasn't changed */ -bool compare_record(TABLE *table) +/** + True if the table's input and output record buffers are comparable using + compare_records(TABLE*). + */ +bool records_are_comparable(const TABLE *table) { + return ((table->file->ha_table_flags() & HA_PARTIAL_COLUMN_READ) == 0) || + bitmap_is_subset(table->write_set, table->read_set); +} + + +/** + Compares the input and outbut record buffers of the table to see if a row + has changed. The algorithm iterates over updated columns and if they are + nullable compares NULL bits in the buffer before comparing actual + data. Special care must be taken to compare only the relevant NULL bits and + mask out all others as they may be undefined. The storage engine will not + and should not touch them. + + @param table The table to evaluate. + + @return true if row has changed. + @return false otherwise. +*/ +bool compare_records(const TABLE *table) { + DBUG_ASSERT(records_are_comparable(table)); + + if ((table->file->ha_table_flags() & HA_PARTIAL_COLUMN_READ) != 0) + { + /* + Storage engine may not have read all columns of the record. Fields + (including NULL bits) not in the write_set may not have been read and + can therefore not be compared. + */ + for (Field **ptr= table->field ; *ptr != NULL; ptr++) + { + Field *field= *ptr; + if (bitmap_is_set(table->write_set, field->field_index)) + { + if (field->real_maybe_null()) + { + uchar null_byte_index= field->null_ptr - table->record[0]; + + if (((table->record[0][null_byte_index]) & field->null_bit) != + ((table->record[1][null_byte_index]) & field->null_bit)) + return TRUE; + } + if (field->cmp_binary_offset(table->s->rec_buff_length)) + return TRUE; + } + } + return FALSE; + } + + /* + The storage engine has read all columns, so it's safe to compare all bits + including those not in the write_set. This is cheaper than the field-by-field + comparison done above. + */ if (table->s->blob_fields + table->s->varchar_fields == 0) + // Fixed-size record: do bitwise comparison of the records return cmp_record(table,record[1]); /* Compare null bits */ if (memcmp(table->null_flags, @@ -186,7 +243,6 @@ int mysql_update(THD *thd, bool using_limit= limit != HA_POS_ERROR; bool safe_update= test(thd->options & OPTION_SAFE_UPDATES); bool used_key_is_modified, transactional_table, will_batch; - bool can_compare_record; int res; int error, loc_error; uint used_index= MAX_KEY, dup_key_found; @@ -575,15 +631,6 @@ int mysql_update(THD *thd, if (table->file->ha_table_flags() & HA_PARTIAL_COLUMN_READ) table->prepare_for_position(); - /* - We can use compare_record() to optimize away updates if - the table handler is returning all columns OR if - if all updated columns are read - */ - can_compare_record= (!(table->file->ha_table_flags() & - HA_PARTIAL_COLUMN_READ) || - bitmap_is_subset(table->write_set, table->read_set)); - while (!(error=info.read_record(&info)) && !thd->killed) { thd->examined_row_count++; @@ -601,7 +648,7 @@ int mysql_update(THD *thd, found++; - if (!can_compare_record || compare_record(table)) + if (!records_are_comparable(table) || compare_records(table)) { if ((res= table_list->view_check_option(thd, ignore)) != VIEW_CHECK_OK) @@ -1695,18 +1742,8 @@ bool multi_update::send_data(List<Item> ¬_used_values) if (table->status & (STATUS_NULL_ROW | STATUS_UPDATED)) continue; - /* - We can use compare_record() to optimize away updates if - the table handler is returning all columns OR if - if all updated columns are read - */ if (table == table_to_update) { - bool can_compare_record; - can_compare_record= (!(table->file->ha_table_flags() & - HA_PARTIAL_COLUMN_READ) || - bitmap_is_subset(table->write_set, - table->read_set)); table->status|= STATUS_UPDATED; store_record(table,record[1]); if (fill_record_n_invoke_before_triggers(thd, *fields_for_table[offset], @@ -1721,7 +1758,7 @@ bool multi_update::send_data(List<Item> ¬_used_values) */ table->auto_increment_field_not_null= FALSE; found++; - if (!can_compare_record || compare_record(table)) + if (!records_are_comparable(table) || compare_records(table)) { int error; if ((error= cur_table->view_check_option(thd, ignore)) != @@ -1908,7 +1945,6 @@ int multi_update::do_updates() DBUG_RETURN(0); for (cur_table= update_tables; cur_table; cur_table= cur_table->next_local) { - bool can_compare_record; uint offset= cur_table->shared; table = cur_table->table; @@ -1945,11 +1981,6 @@ int multi_update::do_updates() if ((local_error = tmp_table->file->ha_rnd_init(1))) goto err; - can_compare_record= (!(table->file->ha_table_flags() & - HA_PARTIAL_COLUMN_READ) || - bitmap_is_subset(table->write_set, - table->read_set)); - for (;;) { if (thd->killed && trans_safe) @@ -1990,7 +2021,7 @@ int multi_update::do_updates() TRG_ACTION_BEFORE, TRUE)) goto err2; - if (!can_compare_record || compare_record(table)) + if (!records_are_comparable(table) || compare_records(table)) { int error; if ((error= cur_table->view_check_option(thd, ignore)) != |