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Posted to codereview@trafodion.apache.org by DaveBirdsall <gi...@git.apache.org> on 2017/04/05 18:25:28 UTC
[GitHub] incubator-trafodion pull request #1046: [TRAFODION-2576] Fix long varchar bu...
GitHub user DaveBirdsall opened a pull request:
https://github.com/apache/incubator-trafodion/pull/1046
[TRAFODION-2576] Fix long varchar bug in incremental UPDATE STATISTICS
You can merge this pull request into a Git repository by running:
$ git pull https://github.com/DaveBirdsall/incubator-trafodion Trafodion2376
Alternatively you can review and apply these changes as the patch at:
https://github.com/apache/incubator-trafodion/pull/1046.patch
To close this pull request, make a commit to your master/trunk branch
with (at least) the following in the commit message:
This closes #1046
----
commit ebf98de2ba8ffd361773df3e42b8813b98ce6691
Author: Dave Birdsall <db...@apache.org>
Date: 2017-04-05T18:23:38Z
[TRAFODION-2576] Fix long varchar bug in incremental UPDATE STATISTICS
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[GitHub] incubator-trafodion pull request #1046: [TRAFODION-2576] Fix long varchar bu...
Posted by zellerh <gi...@git.apache.org>.
Github user zellerh commented on a diff in the pull request:
https://github.com/apache/incubator-trafodion/pull/1046#discussion_r110058006
--- Diff: core/sql/ustat/hs_globals.cpp ---
@@ -1882,6 +1882,55 @@ NABoolean HSColumnStruct::operator==(const HSColumnStruct& other) const
return ( colnum == other.colnum );
}
+//
+// METHOD: addTruncatedColumnReference()
+//
+// PURPOSE: Generates a column reference or a SUBSTRING
+// on a column reference which truncates the
+// column to the maximum length allowed in
+// UPDATE STATISTICS.
+//
+// INPUT: 'qry' - the SQL query string to append the
+// reference to.
+// 'colInfo' - struct containing datatype info
+// about the column.
+//
+void HSColumnStruct::addTruncatedColumnReference(NAString & qry)
+ {
+ HSGlobalsClass *hs_globals = GetHSContext();
+ Lng32 maxLengthInBytes = hs_globals->maxCharColumnLengthInBytes;
+ bool isOverSized = DFS2REC::isAnyCharacter(datatype) &&
+ (length > maxLengthInBytes);
+ if (isOverSized)
+ {
+ // Note: The result data type of SUBSTRING is VARCHAR, always.
+ // But if the column is CHAR, many places in the ustat code are not
+ // expecting a VARCHAR. So, we stick a CAST around it to convert
+ // it back to a CHAR in these cases.
+
+ NABoolean isFixedChar = DFS2REC::isSQLFixedChar(datatype);
+ if (isFixedChar)
+ qry += "CAST(";
+ qry += "SUBSTRING(";
+ qry += externalColumnName->data();
+ qry += " FOR ";
+
+ char temp[20]; // big enough for "nnnnnn)"
+ sprintf(temp,"%d)", maxLengthInBytes / CharInfo::maxBytesPerChar(charset));
+ qry += temp;
+ if (isFixedChar)
+ {
+ qry += " AS CHAR(";
+ qry += temp;
+ qry += ")";
--- End diff --
... or, actually, make it universally BYTES when the charset is UTF-8. That probably makes more sense, as the information content is then roughly the same.
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[GitHub] incubator-trafodion pull request #1046: [TRAFODION-2576] Fix long varchar bu...
Posted by asfgit <gi...@git.apache.org>.
Github user asfgit closed the pull request at:
https://github.com/apache/incubator-trafodion/pull/1046
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[GitHub] incubator-trafodion pull request #1046: [TRAFODION-2576] Fix long varchar bu...
Posted by DaveBirdsall <gi...@git.apache.org>.
Github user DaveBirdsall commented on a diff in the pull request:
https://github.com/apache/incubator-trafodion/pull/1046#discussion_r110201855
--- Diff: core/sql/ustat/hs_globals.cpp ---
@@ -1882,6 +1882,55 @@ NABoolean HSColumnStruct::operator==(const HSColumnStruct& other) const
return ( colnum == other.colnum );
}
+//
+// METHOD: addTruncatedColumnReference()
+//
+// PURPOSE: Generates a column reference or a SUBSTRING
+// on a column reference which truncates the
+// column to the maximum length allowed in
+// UPDATE STATISTICS.
+//
+// INPUT: 'qry' - the SQL query string to append the
+// reference to.
+// 'colInfo' - struct containing datatype info
+// about the column.
+//
+void HSColumnStruct::addTruncatedColumnReference(NAString & qry)
+ {
+ HSGlobalsClass *hs_globals = GetHSContext();
+ Lng32 maxLengthInBytes = hs_globals->maxCharColumnLengthInBytes;
+ bool isOverSized = DFS2REC::isAnyCharacter(datatype) &&
+ (length > maxLengthInBytes);
+ if (isOverSized)
+ {
+ // Note: The result data type of SUBSTRING is VARCHAR, always.
+ // But if the column is CHAR, many places in the ustat code are not
+ // expecting a VARCHAR. So, we stick a CAST around it to convert
+ // it back to a CHAR in these cases.
+
+ NABoolean isFixedChar = DFS2REC::isSQLFixedChar(datatype);
+ if (isFixedChar)
+ qry += "CAST(";
+ qry += "SUBSTRING(";
+ qry += externalColumnName->data();
+ qry += " FOR ";
+
+ char temp[20]; // big enough for "nnnnnn)"
+ sprintf(temp,"%d)", maxLengthInBytes / CharInfo::maxBytesPerChar(charset));
+ qry += temp;
+ if (isFixedChar)
+ {
+ qry += " AS CHAR(";
+ qry += temp;
+ qry += ")";
--- End diff --
Thanks for these comments. Your analysis is correct. The code is limiting strings to 256 bytes, which for UTF-8 means 64 characters since the longest UTF-8 character is 4 bytes long.
By the way, the 256 byte limit is controllable by CQD so a customer or user can increase this if they wish. The CQD is USTAT_MAX_CHAR_COL_LENGTH_IN_BYTES.
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reply appear on GitHub as well. If your project does not have this feature
enabled and wishes so, or if the feature is enabled but not working, please
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[GitHub] incubator-trafodion pull request #1046: [TRAFODION-2576] Fix long varchar bu...
Posted by zellerh <gi...@git.apache.org>.
Github user zellerh commented on a diff in the pull request:
https://github.com/apache/incubator-trafodion/pull/1046#discussion_r110052947
--- Diff: core/sql/ustat/hs_globals.cpp ---
@@ -1882,6 +1882,55 @@ NABoolean HSColumnStruct::operator==(const HSColumnStruct& other) const
return ( colnum == other.colnum );
}
+//
+// METHOD: addTruncatedColumnReference()
+//
+// PURPOSE: Generates a column reference or a SUBSTRING
+// on a column reference which truncates the
+// column to the maximum length allowed in
+// UPDATE STATISTICS.
+//
+// INPUT: 'qry' - the SQL query string to append the
+// reference to.
+// 'colInfo' - struct containing datatype info
+// about the column.
+//
+void HSColumnStruct::addTruncatedColumnReference(NAString & qry)
+ {
+ HSGlobalsClass *hs_globals = GetHSContext();
+ Lng32 maxLengthInBytes = hs_globals->maxCharColumnLengthInBytes;
+ bool isOverSized = DFS2REC::isAnyCharacter(datatype) &&
+ (length > maxLengthInBytes);
+ if (isOverSized)
+ {
+ // Note: The result data type of SUBSTRING is VARCHAR, always.
+ // But if the column is CHAR, many places in the ustat code are not
+ // expecting a VARCHAR. So, we stick a CAST around it to convert
+ // it back to a CHAR in these cases.
+
+ NABoolean isFixedChar = DFS2REC::isSQLFixedChar(datatype);
+ if (isFixedChar)
+ qry += "CAST(";
+ qry += "SUBSTRING(";
+ qry += externalColumnName->data();
+ qry += " FOR ";
+
+ char temp[20]; // big enough for "nnnnnn)"
+ sprintf(temp,"%d)", maxLengthInBytes / CharInfo::maxBytesPerChar(charset));
+ qry += temp;
+ if (isFixedChar)
+ {
+ qry += " AS CHAR(";
+ qry += temp;
+ qry += ")";
--- End diff --
This is a question to this pre-existing code: We added character and byte semantics, like Oracle has it, to UTF-8 character columns. Do we need something similar here? Maybe as simple as adding the keyword "BYTES" when we deal with UTF-8 character columns with a length specified in bytes?
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[GitHub] incubator-trafodion pull request #1046: [TRAFODION-2576] Fix long varchar bu...
Posted by zellerh <gi...@git.apache.org>.
Github user zellerh commented on a diff in the pull request:
https://github.com/apache/incubator-trafodion/pull/1046#discussion_r110060012
--- Diff: core/sql/ustat/hs_globals.cpp ---
@@ -1882,6 +1882,55 @@ NABoolean HSColumnStruct::operator==(const HSColumnStruct& other) const
return ( colnum == other.colnum );
}
+//
+// METHOD: addTruncatedColumnReference()
+//
+// PURPOSE: Generates a column reference or a SUBSTRING
+// on a column reference which truncates the
+// column to the maximum length allowed in
+// UPDATE STATISTICS.
+//
+// INPUT: 'qry' - the SQL query string to append the
+// reference to.
+// 'colInfo' - struct containing datatype info
+// about the column.
+//
+void HSColumnStruct::addTruncatedColumnReference(NAString & qry)
+ {
+ HSGlobalsClass *hs_globals = GetHSContext();
+ Lng32 maxLengthInBytes = hs_globals->maxCharColumnLengthInBytes;
+ bool isOverSized = DFS2REC::isAnyCharacter(datatype) &&
+ (length > maxLengthInBytes);
+ if (isOverSized)
+ {
+ // Note: The result data type of SUBSTRING is VARCHAR, always.
+ // But if the column is CHAR, many places in the ustat code are not
+ // expecting a VARCHAR. So, we stick a CAST around it to convert
+ // it back to a CHAR in these cases.
+
+ NABoolean isFixedChar = DFS2REC::isSQLFixedChar(datatype);
+ if (isFixedChar)
+ qry += "CAST(";
+ qry += "SUBSTRING(";
+ qry += externalColumnName->data();
+ qry += " FOR ";
+
+ char temp[20]; // big enough for "nnnnnn)"
+ sprintf(temp,"%d)", maxLengthInBytes / CharInfo::maxBytesPerChar(charset));
+ qry += temp;
+ if (isFixedChar)
+ {
+ qry += " AS CHAR(";
+ qry += temp;
+ qry += ")";
--- End diff --
... thinking about this again, we don't have a SUBSTRING method that will give the first n _bytes_ of a UTF-8 string, truncated to the next UTF-8 character. So, without such a function we can't really do what I suggested above.
If we have a long UTF-8 column c and maxLengthInBytes is 256, then we will take SUBSTRING(c for 64) here. In many situations and languages, this will be about 64 bytes of information, not 256.
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