Download Sequence Generator Pro
Wei Spinks
This form allows you to generate randomized sequences of integers. The randomness comes from atmospheric noise, which for many purposes is better than the pseudo-random number algorithms typically used in computer programs.
Note: A randomized sequence does not contain duplicates (the numbers are like raffle tickets drawn from a hat). There is also the Integer Generator which generates the numbers independently of each other (like rolls of a die) and where each number can occur more than once.
It is super long as I end up turn off guiding in SGP and continue with the sequence. However I tried to reproduce the issue several times. I believe one occurs from around 19:57:55 after automatic center success. The log is probably a little messy but I appreciate if you can take a look.
I am planning to write a sequence generator which will be used in my REST resource implementation class during post to generateunique id. Since every post request is handled by separate thread,I made the variable volatile and method synchronized. I don't have option to use sequences or something which traditional RDBMS provides.
So, okay, so adding "initialValue=500" and updating my DDL scripts to "START 500" fixes this but now my numbering starts at 500 instead of 1. What gives? Is this an EclipseLink bug or is there something I am not understanding. I would like to generate sequences that start at 1 and have allocation sizes that are tuned to the entity (in this case 500). How would I do that with EclipseLink?
Defines a primary key generator that may be referenced by name when a generator element is specified for the GeneratedValue annotation. A sequence generator may be specified on the entity class or on the primary key field or property. The scope of the generator name is global to the persistence unit (across all generator types). Example: @SequenceGenerator(name="EMP_SEQ", allocationSize=25) Since: Java Persistence 1.0Required Element Summary java.lang.Stringname
(Required) A unique generator name that can be referenced by one or more classes to be the generator for primary key values. Optional Element Summary intallocationSize
(Optional) The amount to increment by when allocating sequence numbers from the sequence. java.lang.Stringcatalog
(Optional) The catalog of the sequence generator. intinitialValue
(Optional) The value from which the sequence object is to start generating. java.lang.Stringschema
(Optional) The schema of the sequence generator. java.lang.StringsequenceName
(Optional) The name of the database sequence object from which to obtain primary key values. Element Detailnamepublic abstract java.lang.String name(Required) A unique generator name that can be referenced by one or more classes to be the generator for primary key values.sequenceNamepublic abstract java.lang.String sequenceName(Optional) The name of the database sequence object from which to obtain primary key values. Defaults to a provider-chosen value.Default:""catalogpublic abstract java.lang.String catalog(Optional) The catalog of the sequence generator.Since: Java Persistence 2.0Default:""schemapublic abstract java.lang.String schema(Optional) The schema of the sequence generator.Since: Java Persistence 2.0Default:""initialValuepublic abstract int initialValue(Optional) The value from which the sequence object is to start generating.Default:1allocationSizepublic abstract int allocationSize(Optional) The amount to increment by when allocating sequence numbers from the sequence.Default:50 Overview Package Class Tree Deprecated Index Help PREV CLASS NEXT CLASS FRAMES NO FRAMES All Classes SUMMARY: REQUIRED OPTIONALDETAIL: ELEMENTSubmit a bug or feature Copyright 2009-2011, Oracle Corporation and/or its affiliates. All Rights Reserved. Use is subject to license terms. Generated on 10-February-2011 12:41 var s_code=s.t();if(s_code)document.write(s_code)Scripting on this page tracks web page traffic,but does not change the content in any way.
CREATE SEQUENCE creates a new sequence number generator. This involves creating and initializing a new special single-row table with the name name. The generator will be owned by the user issuing the command.
If a schema name is given then the sequence is created in the specified schema. Otherwise it is created in the current schema. Temporary sequences exist in a special schema, so a schema name cannot be given when creating a temporary sequence. The sequence name must be distinct from the name of any other relation (table, sequence, index, view, materialized view, or foreign table) in the same schema.
to examine the parameters and current state of a sequence. In particular, the last_value field of the sequence shows the last value allocated by any session. (Of course, this value might be obsolete by the time it's printed, if other sessions are actively doing nextval calls.)
If specified, the sequence object is created only for this session, and is automatically dropped on session exit. Existing permanent sequences with the same name are not visible (in this session) while the temporary sequence exists, unless they are referenced with schema-qualified names.
If specified, the sequence is created as an unlogged sequence. Changes to unlogged sequences are not written to the write-ahead log. They are not crash-safe: an unlogged sequence is automatically reset to its initial state after a crash or unclean shutdown. Unlogged sequences are also not replicated to standby servers.
Unlike unlogged tables, unlogged sequences do not offer a significant performance advantage. This option is mainly intended for sequences associated with unlogged tables via identity columns or serial columns. In those cases, it usually wouldn't make sense to have the sequence WAL-logged and replicated but not its associated table.
The optional clause AS data_type specifies the data type of the sequence. Valid types are smallint, integer, and bigint. bigint is the default. The data type determines the default minimum and maximum values of the sequence.
The optional clause INCREMENT BY increment specifies which value is added to the current sequence value to create a new value. A positive value will make an ascending sequence, a negative one a descending sequence. The default value is 1.
The optional clause MINVALUE minvalue determines the minimum value a sequence can generate. If this clause is not supplied or NO MINVALUE is specified, then defaults will be used. The default for an ascending sequence is 1. The default for a descending sequence is the minimum value of the data type.
The optional clause MAXVALUE maxvalue determines the maximum value for the sequence. If this clause is not supplied or NO MAXVALUE is specified, then default values will be used. The default for an ascending sequence is the maximum value of the data type. The default for a descending sequence is -1.
The optional clause CACHE cache specifies how many sequence numbers are to be preallocated and stored in memory for faster access. The minimum value is 1 (only one value can be generated at a time, i.e., no cache), and this is also the default.
The CYCLE option allows the sequence to wrap around when the maxvalue or minvalue has been reached by an ascending or descending sequence respectively. If the limit is reached, the next number generated will be the minvalue or maxvalue, respectively.
The OWNED BY option causes the sequence to be associated with a specific table column, such that if that column (or its whole table) is dropped, the sequence will be automatically dropped as well. The specified table must have the same owner and be in the same schema as the sequence. OWNED BY NONE, the default, specifies that there is no such association.
Furthermore, although multiple sessions are guaranteed to allocate distinct sequence values, the values might be generated out of sequence when all the sessions are considered. For example, with a cache setting of 10, session A might reserve values 1..10 and return nextval=1, then session B might reserve values 11..20 and return nextval=11 before session A has generated nextval=2. Thus, with a cache setting of one it is safe to assume that nextval values are generated sequentially; with a cache setting greater than one you should only assume that the nextval values are all distinct, not that they are generated purely sequentially. Also, last_value will reflect the latest value reserved by any session, whether or not it has yet been returned by nextval.
Firstly, is it possible to create a sequence generator using parameters in the create statement? I would like to be able pass the sequence name start value increment value and max values as parameters.
The reasons for these questions are because the application I am writing uses a sequence generator that I created and I would like to see if I can modify it to use a sequence generator instead of keeping track of these counters in a table.
The scenario is this, the key field in my primary table is a four position text field. The first character is the first letter of a card name, the remainder of the key is a sequence number. The start value is 1 and the max value is 999. The name of the sequence is TableName_Letter. As an example. Card Name starts with A and Table Name is tblCards. Sequence Name is tblCards_A and key looks like A001.
When the counter portion of the sequence maxes out the prefix changes to AA and max value becomes 99. This process continues until the key eventually reaches AZZZ and at that point the sequence has been maxed out.
I see the possibility for this to work using sequences if I can just work out a few details. The first being creating the sequence using parameters The second being keeping track of the rolling prefixes. I'm thinking that can be done in the name of the sequence itself because every time the prefix gets modified it would require dropping the current sequence and creating a new one with new starting value and new max value. For instance the first roll over for a sequence starting with A would be AA it's start value would be 1 and it's max value would be 99 so it's name could be tblCards_AA.
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