Re: Fix for Index Advisor related hooks - Mailing list pgsql-hackers
| From | Gurjeet Singh |
|---|---|
| Subject | Re: Fix for Index Advisor related hooks |
| Date | |
| Msg-id | AANLkTikJ2FoECrxX81LvUySyt_hv04yoq5QBx0Yz=xp_@mail.gmail.com Whole thread Raw |
| In response to | Re: Fix for Index Advisor related hooks (Tom Lane <tgl@sss.pgh.pa.us>) |
| Responses |
Re: Fix for Index Advisor related hooks
|
| List | pgsql-hackers |
On Tue, Feb 15, 2011 at 12:51 PM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
They need to be unique for a run a session, and be distinguishable from normal indexes so that explain_get_index_name_hook() can get a generated name for the hypothetical index.
Currently there are 2 sites interested in knowing if an index is hypothetical:
1) explain_get_index_name_hook
2) get_actual_variable_range()
With this bool isHypothetical in place, explain_get_index_name() would be unchanged, and the Index Advisor can use a locally generated Oid (not from pg_class) to uniquely identify a hypothetical index.
And get_actual_variable_range() would be changed so:
- if (!OidIsValid(index->indexoid))
+ if (index->ishypothetical)
I can code submit a patch for that.
BTW, you use the term 'fictitious' in the comments, would it be better to standardize the term used for such an index? So either the comment would be changed to call it hypothetical, or the structure member would be changed to isfictitious.Gurjeet Singh <singh.gurjeet@gmail.com> writes:> On Tue, Feb 15, 2011 at 8:24 AM, Heikki Linnakangas <
> heikki.linnakangas@enterprisedb.com> wrote:
>> On 11.02.2011 22:44, Gurjeet Singh wrote:>>> One one hand get_actual_variable_range() expects that virtual indexes do
>>> not
>>> have an OID assigned, on the other hand explain_get_index_name_hook() is
>>> handed just an index's OID to get its name back; IMHO these are based on
>>> two
>>> conflicting assumptions about whether a virtual index will have an OID
>>> assigned.>> The new hook takes an index oid as argument, so I gather that you resolvedThat seems like a very expensive, and lock-inducing, way of assigning a
>> the contradiction by deciding that fictitious indexes have OIDs. How do you
>> assign those OIDs? Do fictitious indexes have entries in pg_index?
> No, a fictitious index does not touch pg_index. The Index Advisor uses
> GetNewOid(pg_class) to generate a new OID for the fictitious index.
fictitious OID. They don't need to be globally unique.
They need to be unique for a run a session, and be distinguishable from normal indexes so that explain_get_index_name_hook() can get a generated name for the hypothetical index.
I suggest you
consider the idea I suggested back in 2007:
* In this toy example we just assign all hypothetical indexes
* OID 0, and the explain_get_index_name hook just prints
* <hypothetical index>. In a realistic situation we'd probably
* assume that OIDs smaller than, say, 100 are never the OID of
* any real index, allowing us to identify one of up to 100
* hypothetical indexes per plan. Then we'd need to save aside
* some state data that would let the explain hooks print info
* about the selected index.
As far as the immediate problem goes, I agree that
get_actual_variable_range is mistaken, but I think a cleaner and cheaper
solution would be to add a bool "hypothetical" to IndexOptInfo.
Currently there are 2 sites interested in knowing if an index is hypothetical:
1) explain_get_index_name_hook
2) get_actual_variable_range()
With this bool isHypothetical in place, explain_get_index_name() would be unchanged, and the Index Advisor can use a locally generated Oid (not from pg_class) to uniquely identify a hypothetical index.
And get_actual_variable_range() would be changed so:
- if (!OidIsValid(index->indexoid))
+ if (index->ishypothetical)
I can code submit a patch for that.
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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