diff options
| -rw-r--r-- | doc/src/sgml/ref/truncate.sgml | 27 |
1 files changed, 21 insertions, 6 deletions
diff --git a/doc/src/sgml/ref/truncate.sgml b/doc/src/sgml/ref/truncate.sgml index effe903b099..152b6640d8f 100644 --- a/doc/src/sgml/ref/truncate.sgml +++ b/doc/src/sgml/ref/truncate.sgml @@ -1,5 +1,5 @@ <!-- -$PostgreSQL: pgsql/doc/src/sgml/ref/truncate.sgml,v 1.26 2008/05/16 23:36:04 tgl Exp $ +$PostgreSQL: pgsql/doc/src/sgml/ref/truncate.sgml,v 1.27 2008/05/17 23:36:27 tgl Exp $ PostgreSQL documentation --> @@ -151,11 +151,26 @@ TRUNCATE [ TABLE ] <replaceable class="PARAMETER">name</replaceable> [, ... ] <para> Any <command>ALTER SEQUENCE RESTART</> operations performed as a consequence of using the <literal>RESTART IDENTITY</> option are - nontransactional and will not be rolled back. To minimize risk, - these operations are performed only after all the rest of - <command>TRUNCATE</>'s work is done. In practice this will only - be an issue if <command>TRUNCATE</> is performed inside a - transaction block that is aborted afterwards. + nontransactional and will not be rolled back on failure. To minimize + the risk, these operations are performed only after all the rest of + <command>TRUNCATE</>'s work is done. However, there is still a risk + if <command>TRUNCATE</> is performed inside a transaction block that is + aborted afterwards. For example, consider + +<programlisting> +BEGIN; +TRUNCATE TABLE foo RESTART IDENTITY; +COPY foo FROM ...; +COMMIT; +</programlisting> + + If the <command>COPY</> fails partway through, the table data + rolls back correctly, but the sequences will be left with values + that are probably smaller than they had before, possibly leading + to duplicate-key failures or other problems in later transactions. + If this is likely to be a problem, it's best to avoid using + <literal>RESTART IDENTITY</>, and accept that the new contents of + the table will have higher serial numbers than the old. </para> </warning> </refsect1> |