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From DaveBirdsall <...@git.apache.org>
Subject [GitHub] incubator-trafodion pull request #1229: [Trafodion-2734] Create *Trafodion L...
Date Thu, 14 Sep 2017 00:39:34 GMT
Github user DaveBirdsall commented on a diff in the pull request:

    https://github.com/apache/incubator-trafodion/pull/1229#discussion_r138770951
  
    --- Diff: docs/lob_guide/src/asciidoc/_chapters/work_with_lob.adoc ---
    @@ -0,0 +1,738 @@
    +////
    +/**
    +* @@@ START COPYRIGHT @@@
    +*
    +* Licensed to the Apache Software Foundation (ASF) under one
    +* or more contributor license agreements. See the NOTICE file
    +* distributed with this work for additional information
    +* regarding copyright ownership. The ASF licenses this file
    +* to you under the Apache License, Version 2.0 (the
    +* "License"); you may not use this file except in compliance
    +* with the License. You may obtain a copy of the License at
    +*
    +*   http://www.apache.org/licenses/LICENSE-2.0
    +*
    +* Unless required by applicable law or agreed to in writing,
    +* software distributed under the License is distributed on an
    +* "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
    +* KIND, either express or implied. See the License for the
    +* specific language governing permissions and limitations
    +* under the License.
    +*
    +* @@@ END COPYRIGHT @@@
    +*/
    +////
    +
    +[#work with lob]
    += Work with LOB
    +
    +[#create a sql table with lob columns]
    +== Create a SQL Table with LOB Columns
    +
    +When creating a SQL table with LOB columns, following relevant tables and files are created
as well:
    +
    +* One LOB MD table.
    +* Two dependent descriptor tables.
    +* HDFS data file (locates at /user/trafodion/lobs) for each column.
    +
    +[#syntax]
    +== Syntax
    +
    +```
    +CREATE TABLE table-name (lob-column-spec[, lob-column-spec]…)
    +```
    +
    +```
    +lob-column-spec is:
    +column {lob type}
    +
    +lob type is:
    +BLOB | CLOB [({numeric literal} [unit])] [STORAGE 'storage literal']
    +
    +unit is:
    +empty | 
    +K     | 
    +M     | 
    +G 
    +```
    +
    +[#semantics]
    +=== Semantics
    +
    +* `_storage literal_`
    +
    ++
    +Currently Trafodion only support `'EXTERNAL'` here. 
    +
    ++
    +External LOB object that are not managed by Trafodion.
    +
    +* `_empty_`
    +
    ++
    +Number of bytes specified by the numeric literal.
    +
    +* `_K_`
    +
    ++
    +Numeric literal value * 1024.
    +
    +* `_M_`
    +
    ++
    +Numeric literal value * 1024 * 1024.
    +
    +* `_G_`
    +
    ++
    +Numeric literal value * 1024 * 1024 * 1024.
    +
    +[#examples]
    +=== Examples
    +
    +* This example creates a table tlob1 with 2 columns and primary key on the c1.
    +
    ++
    +
    +```
    +CREATE TABLE tlob1 (c1 INT NOT NULL, c2 BLOB, PRIMARY KEY (c1));
    +```
    +
    +* This example creates a table tlob2 with 3 columns and primary key on the c1.
    +
    ++
    +
    +```
    +CREATE TABLE tlob2 (c1 INT NOT NULL, c2 BLOB, c3 CLOB, PRIMARY KEY (c1));
    +```
    +
    +* This example creates a table tlob130txt_limit50 with 2 columns and primary key on the
c1.
    +
    ++
    +
    +```
    +CREATE TABLE tlob130txt_limit50 (c1 INT NOT NULL, c2 CLOB(50), PRIMARY KEY (c1));
    +```
    +
    +* This example creates a table tlob130bin_limit1K with 2 columns and primary key on the
c1.
    +
    ++
    +
    +```
    +CREATE TABLE tlob130bin_limit1K (c1 INT NOT NULL, c2 BLOB(1 K), PRIMARY KEY (c1));
    +```
    +
    +* This example creates a table tlob130ext with 4 columns and primary key on the c1.
    +
    ++
    +
    +```
    +CREATE TABLE tlob130ext (c1 INT NOT NULL, c2 BLOB, c3 CLOB, c4 BLOB STORAGE 'EXTERNAL',
PRIMARY KEY (c1));
    +```
    +
    +[#hdfs location of lob data]
    +=== HDFS Location of LOB Data
    +
    +When a LOB table is created, the underlying LOB data needs to be stored in HDFS.It is
in the /user/trafodion/lobs by default. 
    +
    +All columns of a table that are declared as LOB types will have all their data in one
file derived from the Object UID and the LOB number of that column which gets assigned during
creation.
    +
    +The following is a LOB file with 2 columns you will see 2 files in HDFS:
    +
    +/user/trafodion/lobs /LOBP_03683514167332904796_0001
    +
    +/user/trafodion/lobs/LOBP_03683514167332904796_0002
    +
    +As rows are added to this column, the LOB data for each row gets appended to the corresponding
column’s LOB data file. 
    +
    +[#insert into a sql table containing lob columns]
    +== Insert into a SQL Table Containing LOB Columns
    +
    +[#syntax]
    +=== Syntax
    +
    +```
    +INSERT INTO table-name [(target-col-list)] insert-source
    +```
    +
    +```
    +target-col-list is: 
    +colname[, colname]... 
    +
    +insert-source is: 
    +VALUES(lob_query-expr[, lob_query-expr])
    +
    +lob_query-expr is: 
    +NULL | ?                                                                     |
    +EMPTY_BLOB()                                                                 |
    +EMPTY_CLOB()                                                                 |      
                              
    +STRINGTOLOB('string literal expression')                                     |
    +FILETOLOB('lob source file name')                                            |
    +BUFFERTOLOB(LOCATION lob source buffer address, LENGTH lob length value)     |
    +EXTERNALTOLOB('external lob source file name')              
    +
    +lob source file name is:
    +hdfs:///{local hdfs file name}     |  
    +{local linux file name}            |
    +{file:///linux file name} 
    +
    +external lob source file name is: 
    +hdfs:///{local hdfs file name}
    +``` 
    +[#semantics]
    +=== Semantics
    +
    +* `_EMPTY_BLOB(), EMPTY_CLOB()_`
    ++
    +Returns an empty LOB handle.     
    +
    +* `_STRINGTOLOB_`
    ++
    +Converts a simple string literal into LOB format. 
    +
    +** `_string literal expression_`
    ++
    +is a series of characters enclosed in single quotes.
    +
    +* `_FILETOLOB_`
    ++
    +Converts data from a local linux/hdfs file into LOB format.
    +
    +* `_BUFFERTOLOB_`
    ++
    +Takes an address and a size of an input buffer, and converts the data pointed to by that
buffer into LOB. 
    +
    +** `_lob source buffer address_`
    ++
    +The long value of the user buffer address in int64.
    +
    +** `_lob length value_`
    ++
    +The length of the user specified lob buffer in int64.
    +
    +[#considerations]
    +=== Considerations
    +
    +The source for inserting into a LOB can be any of the following:
    +
    +* A parameter.
    ++
    +An unnamed parameter can be used to prepare a statement and then during an execution,
either a function or a simple string parameter can be passed in which will be converted to
LOB data.
    +
    +* `EMPTY_BLOB()` or `EMPTY_CLOB()` 
    +
    +** If `EMPTY_BLOB()` or `EMPTY_CLOB()` is specified, then a dummy lob handle is created.

    +
    +*** No data is associated with the empty LOBs yet, but these dummy LOB handles can later
be used to populate with new LOB data. If the LOB had data previously associated with it,
it will be erased.
    +
    +*** The dummy LOB handle will get the same datatype as the underlying column.
    ++
    +For example, if the LOB column was defined as `'EXTERNAL'` during table creation, then
the LOB column gets that type. If it’s not defined, then it is considered as a regular LOB.

    +
    +** An empty LOB is distinct from a LOB containing a string of length zero or a null LOB.
    +
    +* An in-memory LOB which is a simple string data. 
    --- End diff --
    
    Grammar: "is simple string data" sounds better to my ears. (The reason is that "data"
is plural. Though increasingly "data" in everyday English is often construed as singular.
But my ears are old.)


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