Re: Patch to add a primary key using an existing index

UNIQUE constraints suffer from the same behavior; feel like fixing that too? :)

On Oct 9, 2010, at 1:07 PM, Gurjeet Singh wrote:

> This is a continuation from this thread: http://archives.postgresql.org/pgsql-hackers/2010-09/msg02153.php
>
> The attached patch allows creating a primary key using an existing index.
>
> This capability would be helpful in situations where one wishes to rebuild/reindex the primary key, but associated
downtimeis not desirable. It also allows one to create a table and start using it, while creating a unique index
'concurrently'and later adding the primary key using the concurrently built index. Maybe pg_dump can also use it. 
>
> The command syntax is:
>
> ALTER TABLE sometable ADD PRIMARY KEY( col1, col2 ) WITH ( INDEX = 'indexname' );
>
> A typical use case:
>
> CREATE INDEX CONCURRENTLY new_pkey_idx ON sometable( a, b );
>
> ALTER TABLE sometable ADD PRIMARY KEY ( a, b ) WITH (INDEX = 'new_pkey_idx' );
>
> - OR -
>
> ALTER TABLE sometable DROP CONSTRAINT sometable_pkey,
>       ADD PRIMARY KEY ( a, b ) WITH (INDEX = 'new_pkey_idx' );
>
>
> Notes for the reviewers:
> ------------------------
>
> Don't be scared by the size of changes to index.c :) These are mostly indentation diffs. I have attached two versions
ofthe patch: one is context diff, and the other is the same except ignoring whitespace changes. 
>
> The pseudocode is as follows:
>
> In ATExecAddIndex()
>     If this ALTER command specifies a PRIMARY KEY
>       Call get_pkey_index_oid() to perform checks.
>
> In get_pkey_index_oid()
>     Look for the WITH INDEX option
>     Reject
>         if more than one WITH INDEX clause specified
>         if the index doesn't exist or not found in table's schema
>         if the index is associated with any CONSTRAINT
>         if index is not ready or not valid (CONCURRENT buiild? Canceled CONCURRENT?)
>         if index is on some other table
>         if index is not unique
>         if index is an expression index
>         if index is a partial index
>         if index columns do not match the PRIMARY KEY clause in the command
>         if index is not B-tree
>     If PRIMARY KEY clause doesn't have a constraint name, assign it one. (code comments explain why)
>     Rename the index to match constraint name in the PRIMARY KEY clause
>
> Back in ATExecAddIndex()
>     Use the index OID returned by get_pkey_index_oid() to tell DefineIndex() to not create index.
>     Now mark the index as having 'indisprimary' flag.
>
> In DefineIndex() and index_create() APIs
>     pass an additional flag: index_exists
>     Skip various actions based on this flag.
>
>
> The patch contains a few tests, and doesn't yet have a docs patch.
>
> The development branch is at http://github.com/gurjeet/postgres/tree/replace_pkey_index
>
> Regards,
> --
> gurjeet.singh
> @ EnterpriseDB - The Enterprise Postgres Company
> http://www.EnterpriseDB.com
>
> singh.gurjeet@{ gmail | yahoo }.com
> Twitter/Skype: singh_gurjeet
>
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> <add_pkey_with_index.patch><add_pkey_with_index.ignore_ws.patch>
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--
Jim C. Nasby, Database Architect                   jim@nasby.net
512.569.9461 (cell)                         http://jim.nasby.net