database/postgres
1
0
Fork 0
mirror of https://github.com/postgres/postgres.git synced 2025-07-18 17:42:25 +03:00
Code Activity

SGML updates from post 6.3.2 manual changes. Added pg_upgrade man page.

Browse Source
This commit is contained in:
Bruce Momjian
1998-10-15 05:47:04 +00:00
parent 31bca4540e
commit 3c4e2bc9be
10 changed files with 464 additions and 296 deletions
Download Patch File Download Diff File Expand all files Collapse all files

40
doc/src/sgml/ref/create_sequence.sgml
View File

@ -68,7 +68,7 @@ CREATE SEQUENCE <replaceable class="parameter">seqname</replaceable>
The optional clause <option>MINVALUE
<replaceable class="parameter">minvalue</replaceable></option>
determines the minimum value
a sequence can be. The defaults are 1 and -2147483647 for
a sequence can generate. The defaults are 1 and -2147483647 for
ascending and descending sequences, respectively.
</PARA>
</LISTITEM>
@ -113,7 +113,8 @@ CREATE SEQUENCE <replaceable class="parameter">seqname</replaceable>
The <option>CACHE <replaceable class="parameter">cache</replaceable></option> option
enables sequence numbers to be preallocated
and stored in memory for faster access. The minimum
value is 1 (no cache) and this is also the default.
value is 1 (only one value can be generated at a time, i.e. no cache)
and this is also the default.
</PARA>
</LISTITEM>
</VARLISTENTRY>
@ -223,12 +224,12 @@ CREATE SEQUENCE <replaceable class="parameter">seqname</replaceable>
<PARA>
CREATE SEQUENCE will enter a new sequence number generator
into the current data base. This involves creating and initialising a
new single block
new single-row
table with the name <replaceable class="parameter">seqname</replaceable>.
The generator will be "owned" by the user issuing the command.
</PARA>
<para>
After the sequence is created, you may use the function
After a sequence is created, you may use the function
<function>nextval(<replaceable class="parameter">seqname</replaceable>)</function>
to get a new number from the sequence.
The function
@ -245,11 +246,42 @@ The function
SELECT * FROM sequence_name;
</programlisting>
to get the parameters of a sequence.
Aside from fetching the original
parameters, you can use
<programlisting>
SELECT last_value FROM sequence_name;
</programlisting>
to obtain the last value allocated by any backend.
parameters, you can use
</para>
<para>
Low-level locking is used to enable multiple simultaneous
calls to a generator.
</para>
<para>
<TITLE>
NOTE:
</TITLE>
Unexpected results may be obtained if a cache setting greater than one
is used for a sequence object that will be used concurrently by multiple
backends. Each backend will allocate "cache" successive sequence values
during one access to the sequence object and increase the sequence
object's last_value accordingly. Then, the next cache-1 uses of nextval
within that backend simply return the preallocated values without touching
the shared object. So, numbers allocated but not used in the current session
will be lost. Furthermore, although multiple backends are guaranteed to
allocate distinct sequence values, the values may be generated out of
sequence when all the backends are considered. (For example, with a cache
setting of 10, backend A might reserve values 1..10 and return nextval=1, then
backend B might reserve values 11..20 and return nextval=11 before backend
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 backend,
whether or not it has yet been returned by nextval.
</para>
<REFSECT2 ID="R2-SQL-CREATESEQUENCE-3">
<REFSECT2INFO>