| Bug #32095 | data has different result for double type with/without ps-protocol | ||
|---|---|---|---|
| Submitted: | 5 Nov 2007 7:26 | Modified: | 23 Jan 2008 16:28 |
| Reporter: | Guangbao Ni | Email Updates: | |
| Status: | Closed | Impact on me: | |
| Category: | MySQL Server | Severity: | S3 (Non-critical) |
| Version: | 5.1.22 | OS: | Any |
| Assigned to: | CPU Architecture: | Any | |
| Tags: | ps-protocol, server | ||
[5 Nov 2007 8:53]
Guangbao Ni
It is a normal server bug, and not relate to replication and ndb storage engine. the following is the simple example test case that you can reproduce it: USE test; CREATE TABLE t1 (c1 INT KEY,d DOUBLE UNSIGNED); INSERT INTO t1 VALUES(13, 1.7976931348623157E+308); SELECT * FROM t1 ORDER BY c1; DROP TABLE t1;
[7 Nov 2007 4:00]
Bugs System
A patch for this bug has been committed. After review, it may be pushed to the relevant source trees for release in the next version. You can access the patch from: http://lists.mysql.com/commits/37236 ChangeSet@1.2669, 2007-11-07 11:48:11+08:00, gni@dev3-221.dev.cn.tlan +15 -0 WL#3829 Extending testing of the online alter table Fix the problem caused by bug#32095 Here just shorten the double type and avoid the problem. Because the bug#32095 has been comment in rpl_ndb_add_column.test, Don't want to be affected more than twice by the bug.
[14 Dec 2007 17:09]
Bugs System
Pushed into 6.0.5-alpha
[23 Jan 2008 16:28]
Paul DuBois
Noted in 6.0.5 changelog. String-to-double conversion was performed differently when the prepared-statement protocol was used from when it was not.
Description: When insert and update a double type in master, and slave shows different result with ps-protocol and without ps-protocol. the number of digitals is greater than 15. How to repeat: for example: --connection master CREATE TABLE t1 (c1 INT KEY) ROW_FORMAT=DYNAMIC ENGINE=NDB; ALTER ONLINE TABLE t1 ADD d DOUBLE UNSIGNED; INSERT INTO t1 VALUES(13, 1.7976931348623157E+308); --sync_slave_with_master connection slave; SELECT * FROM t1 ORDER BY c1; Suggested fix: The following is explanated by Alexey. The diff is actually visible, note "1.7976931348623e+308" instead of "1.79769313486232e+308". The reason is in how the double-to-string conversion is performed. With ps protocol disabled the conversion is performed by the server in Field_double::val_str() which uses DBL_DIG = 15 as precision for "%g": if (dec >= NOT_FIXED_DEC) { sprintf(to,"%-*.*g",(int) field_length,DBL_DIG,nr); to=strcend(to,' '); } With ps protocol enabled the conversion is performed by the client library in fetch_float_with_conversion() which uses 14 as precision for "%g": /* The 14 below is to ensure that the server and client has the same precisions. This will ensure that on the same machine you get the same value as a string independent of the protocol you use. */ sprintf(buff, "%-*.*g", (int) min(sizeof(buff)-1, param->buffer_length), min(14,width), value); end= strcend(buff, ' '); *end= 0; Hence the difference in rounding. Thank you, Alexey for your explanation!