Thread: pg_depend
I have found that many TODO items would benefit from a pg_depend table that tracks object dependencies. TODO updated. --------------------------------------------------------------------------- DEPENDENCY CHECKING / pg_depend * Auto-destroy sequence on DROP of table with SERIAL, perhaps with a separate SERIAL type * Prevent column dropping if column is used by foreign key * Propagate column or table renaming to foreign key constraints * Automatically drop constraints/functions when object is dropped * Make constraints clearer in dump file * Make foreign keys easier to identify -- Bruce Momjian | http://candle.pha.pa.us pgman@candle.pha.pa.us | (610) 853-3000+ If your life is a hard drive, | 830 Blythe Avenue + Christ can be your backup. | Drexel Hill, Pennsylvania19026
Bruce Momjian writes: > I have found that many TODO items would benefit from a pg_depend table > that tracks object dependencies. TODO updated. I'm not so convinced on that idea. Assume you're dropping object foo. You look at pg_depend and see that objects 145928, 264792, and 1893723 depend on it. Great, what do you do now? Every system catalog (except the really badly designed ones) already contains dependency information. What might help is that we make the internal API for altering and dropping any kind of object more consistent and general so that they can call each other in the dependency case. (E.g., make sure none of them require whereToSendOutput or parser state as an argument.) -- Peter Eisentraut peter_e@gmx.net http://funkturm.homeip.net/~peter
> Bruce Momjian writes: > > > I have found that many TODO items would benefit from a pg_depend table > > that tracks object dependencies. TODO updated. > > I'm not so convinced on that idea. Assume you're dropping object foo. > You look at pg_depend and see that objects 145928, 264792, and 1893723 > depend on it. Great, what do you do now? > > Every system catalog (except the really badly designed ones) already > contains dependency information. What might help is that we make the > internal API for altering and dropping any kind of object more consistent > and general so that they can call each other in the dependency case. > (E.g., make sure none of them require whereToSendOutput or parser state as > an argument.) Yes, it is not simple. The table is just one part of it. Code has to do lookups and have cascade/failure options based on what it finds. Things can get quite complicated, especially circular dependencies. It needs a general overhaul and has to hit every area. We need a central location to keep all this info. -- Bruce Momjian | http://candle.pha.pa.us pgman@candle.pha.pa.us | (610) 853-3000+ If your life is a hard drive, | 830 Blythe Avenue + Christ can be your backup. | Drexel Hill, Pennsylvania19026
On Mon, 16 Jul 2001, Peter Eisentraut wrote: > Bruce Momjian writes: > > > I have found that many TODO items would benefit from a pg_depend table > > that tracks object dependencies. TODO updated. > > I'm not so convinced on that idea. Assume you're dropping object foo. > You look at pg_depend and see that objects 145928, 264792, and 1893723 > depend on it. Great, what do you do now? I believe someone else previously suggested this: drop <type> object [RESTRICT | CASCADE] to make use of dependency info. > Every system catalog (except the really badly designed ones) already > contains dependency information. What might help is that we make the > internal API for altering and dropping any kind of object more consistent > and general so that they can call each other in the dependency case. > (E.g., make sure none of them require whereToSendOutput or parser state as > an argument.) Yes, that's definitely requirement to implement the above...
Alex Pilosov writes: > > I'm not so convinced on that idea. Assume you're dropping object foo. > > You look at pg_depend and see that objects 145928, 264792, and 1893723 > > depend on it. Great, what do you do now? > I believe someone else previously suggested this: > > drop <type> object [RESTRICT | CASCADE] > > to make use of dependency info. That was me. The point, however, was, given object id 145928, how the heck to you know what table this comes from? -- Peter Eisentraut peter_e@gmx.net http://funkturm.homeip.net/~peter
On Tue, 17 Jul 2001, Peter Eisentraut wrote: > Alex Pilosov writes: > > > > I'm not so convinced on that idea. Assume you're dropping object foo. > > > You look at pg_depend and see that objects 145928, 264792, and 1893723 > > > depend on it. Great, what do you do now? > > I believe someone else previously suggested this: > > > > drop <type> object [RESTRICT | CASCADE] > > > > to make use of dependency info. > > That was me. The point, however, was, given object id 145928, how the > heck to you know what table this comes from? have a view pg_objecttype which is a UNION across all the [relevant] system tables sounds fine to me, but maybe I'm missing something?
> Alex Pilosov writes: > > > > I'm not so convinced on that idea. Assume you're dropping object foo. > > > You look at pg_depend and see that objects 145928, 264792, and 1893723 > > > depend on it. Great, what do you do now? > > I believe someone else previously suggested this: > > > > drop <type> object [RESTRICT | CASCADE] > > > > to make use of dependency info. > > That was me. The point, however, was, given object id 145928, how the > heck to you know what table this comes from? I think we will need the relid of the system table. I imagine four columns: object relidobject oidreference relidreferences oid -- Bruce Momjian | http://candle.pha.pa.us pgman@candle.pha.pa.us | (610) 853-3000+ If your life is a hard drive, | 830 Blythe Avenue + Christ can be your backup. | Drexel Hill, Pennsylvania19026
Peter Eisentraut <peter_e@gmx.net> writes:
> You look at pg_depend and see that objects 145928, 264792, and 1893723
> depend on it. Great, what do you do now?
>> I believe someone else previously suggested this:
>> drop <type> object [RESTRICT | CASCADE]
>> to make use of dependency info.
> That was me. The point, however, was, given object id 145928, how the
> heck to you know what table this comes from?
Even more to the point, what guarantee can we have that that OID even
defines a unique object at all? We have unique indexes that ensure
there are not two tables with the same OID, or two functions with the
same OID, etc --- but none that ensure uniqueness across system
catalogs.
The objects would need to be identified by two-part IDs, one part
specifying the object type and one giving its OID (which is known unique
within that type). Possibly object type would be best handled by giving
the OID of the system catalog containing the object's definition row.
In any case, looking at the type part would let users of the pg_depend
catalog figure out what they needed to do.
BTW, pg_description is broken because it assumes that OID alone is a
sufficient identifier ... but since it's such a noncritical function,
I haven't gotten too excited about it.
regards, tom lane
Let me clearify. I am suggesting system table relid for each entry: > object sysrelid > object oid > reference sysrelid > references oid -- Bruce Momjian | http://candle.pha.pa.us pgman@candle.pha.pa.us | (610) 853-3000+ If your life is a hard drive, | 830 Blythe Avenue + Christ can be your backup. | Drexel Hill, Pennsylvania19026
On Tue, 17 Jul 2001, Peter Eisentraut wrote: > Alex Pilosov writes: > > > > I'm not so convinced on that idea. Assume you're dropping object foo. > > > You look at pg_depend and see that objects 145928, 264792, and 1893723 > > > depend on it. Great, what do you do now? > > I believe someone else previously suggested this: > > > > drop <type> object [RESTRICT | CASCADE] > > > > to make use of dependency info. > > That was me. The point, however, was, given object id 145928, how the > heck to you know what table this comes from? You have three columns, depender, dependee, and the third the oid of the entry of pg_class describing what the depender is. Oh, actually you'd probably need four columns, depender, dependee, depender in pg_class, and dependee in pg_class. Take care, Bill
> The objects would need to be identified by two-part IDs, one part > specifying the object type and one giving its OID (which is known unique > within that type). Possibly object type would be best handled by giving > the OID of the system catalog containing the object's definition row. > In any case, looking at the type part would let users of the pg_depend > catalog figure out what they needed to do. Yes, exactly. Also, I can see code that will handles dependencies differently if it is a pg_class or pg_type row that is mentioned in pg_depend. -- Bruce Momjian | http://candle.pha.pa.us pgman@candle.pha.pa.us | (610) 853-3000+ If your life is a hard drive, | 830 Blythe Avenue + Christ can be your backup. | Drexel Hill, Pennsylvania19026
Peter Eisentraut wrote: > > Alex Pilosov writes: > > > > I'm not so convinced on that idea. Assume you're dropping object foo. > > > You look at pg_depend and see that objects 145928, 264792, and 1893723 > > > depend on it. Great, what do you do now? > > I believe someone else previously suggested this: > > > > drop <type> object [RESTRICT | CASCADE] > > > > to make use of dependency info. > > That was me. The point, however, was, given object id 145928, how the > heck to you know what table this comes from? > Is it really determined that *DROP OBJECT* drops the objects which are dependent on it ? regards, Hiroshi Inoue
On Tue, 17 Jul 2001, Hiroshi Inoue wrote: > Peter Eisentraut wrote: > > > > Alex Pilosov writes: > > > > > drop <type> object [RESTRICT | CASCADE] > > > > > > to make use of dependency info. > > > > That was me. The point, however, was, given object id 145928, how the > > heck to you know what table this comes from? > > > > Is it really determined that *DROP OBJECT* drops the objects > which are dependent on it ? If you used DROP OBJECT CASCADE, yes. That's what CASCADE is saying. I think the idea is that you can say what happens - delete dependents, or do something else. Take care, Bill
Hiroshi Inoue <Inoue@tpf.co.jp> writes:
> Is it really determined that *DROP OBJECT* drops the objects
> which are dependent on it ?
DROP object CASCADE should work that way, because that's what the spec
says.
Whether the default DROP behavior should be CASCADE, RESTRICT, or the
current laissez-faire behavior remains to be debated ;-). The spec
is no help since it has no default: DROP *requires* a CASCADE or
RESTRICT option in SQL92. But I doubt our users will let us get away
with changing the syntax that way. So, once we have the CASCADE and
RESTRICT options implemented, we'll need to decide what an unadorned
DROP should do. Opinions anyone?
regards, tom lane
> Hiroshi Inoue <Inoue@tpf.co.jp> writes: > > Is it really determined that *DROP OBJECT* drops the objects > > which are dependent on it ? > > DROP object CASCADE should work that way, because that's what the spec > says. > > Whether the default DROP behavior should be CASCADE, RESTRICT, or the > current laissez-faire behavior remains to be debated ;-). The spec > is no help since it has no default: DROP *requires* a CASCADE or > RESTRICT option in SQL92. But I doubt our users will let us get away > with changing the syntax that way. So, once we have the CASCADE and > RESTRICT options implemented, we'll need to decide what an unadorned > DROP should do. Opinions anyone? Don't forget RENAME. And what do we do if two items depend on the same object. -- Bruce Momjian | http://candle.pha.pa.us pgman@candle.pha.pa.us | (610) 853-3000+ If your life is a hard drive, | 830 Blythe Avenue + Christ can be your backup. | Drexel Hill, Pennsylvania19026
> Whether the default DROP behavior should be CASCADE, RESTRICT, or the > current laissez-faire behavior remains to be debated ;-). The spec > is no help since it has no default: DROP *requires* a CASCADE or > RESTRICT option in SQL92. But I doubt our users will let us get away > with changing the syntax that way. So, once we have the CASCADE and > RESTRICT options implemented, we'll need to decide what an unadorned > DROP should do. Opinions anyone? Hmmm...an unadorned drop could remove the object without RESRICTing it or CASCADEing it. Hence, if there are objects that depend on it, the object will be removed anyway, and dependent objects will not be touched. It's one of those things that gives the DBA power, but might let them munge their database. (Although it's exactly the same as the current way things happen) Chris
Christopher Kings-Lynne wrote: > > > Whether the default DROP behavior should be CASCADE, RESTRICT, or the > > current laissez-faire behavior remains to be debated ;-). The spec > > is no help since it has no default: DROP *requires* a CASCADE or > > RESTRICT option in SQL92. But I doubt our users will let us get away > > with changing the syntax that way. So, once we have the CASCADE and > > RESTRICT options implemented, we'll need to decide what an unadorned > > DROP should do. Opinions anyone? > > Hmmm...an unadorned drop could remove the object without RESRICTing it or > CASCADEing it. Hence, if there are objects that depend on it, the object > will be removed anyway, and dependent objects will not be touched. We could mark the objects(and their dependent objects) as *INVALID*. They would revive when reference objects revive in the world of *name*s. regards, Hiroshi Inoue
Bruce Momjian writes: > > That was me. The point, however, was, given object id 145928, how the > > heck to you know what table this comes from? > > I think we will need the relid of the system table. I imagine four > columns: > > object relid > object oid > reference relid > references oid I'm not seeing the point. You're essentially duplicating the information that's already available in the system catalogs. This is bound to become a catastrophe the minute a user steps in and does manual surgery on some catalog. (And yes, manual surgery should still be possible.) -- Peter Eisentraut peter_e@gmx.net http://funkturm.homeip.net/~peter
> Bruce Momjian writes: > > > > That was me. The point, however, was, given object id 145928, how the > > > heck to you know what table this comes from? > > > > I think we will need the relid of the system table. I imagine four > > columns: > > > > object relid > > object oid > > reference relid > > references oid > > I'm not seeing the point. You're essentially duplicating the information > that's already available in the system catalogs. This is bound to become > a catastrophe the minute a user steps in and does manual surgery on some > catalog. (And yes, manual surgery should still be possible.) But how then do you find the system table that uses the given oid? Wasn't that your valid complaint? -- Bruce Momjian | http://candle.pha.pa.us pgman@candle.pha.pa.us | (610) 853-3000+ If your life is a hard drive, | 830 Blythe Avenue + Christ can be your backup. | Drexel Hill, Pennsylvania19026
Bruce Momjian writes: > > I'm not seeing the point. You're essentially duplicating the information > > that's already available in the system catalogs. This is bound to become > > a catastrophe the minute a user steps in and does manual surgery on some > > catalog. (And yes, manual surgery should still be possible.) > > But how then do you find the system table that uses the given oid? It's implied by the column you're looking at. -- Peter Eisentraut peter_e@gmx.net http://funkturm.homeip.net/~peter
> Bruce Momjian writes: > > > > I'm not seeing the point. You're essentially duplicating the information > > > that's already available in the system catalogs. This is bound to become > > > a catastrophe the minute a user steps in and does manual surgery on some > > > catalog. (And yes, manual surgery should still be possible.) > > > > But how then do you find the system table that uses the given oid? > > It's implied by the column you're looking at. Is it? Are we going to record dependency both ways, e.g primary table -> foreign table and foreign table -> primary table, or just one of them. And when we see we depend on something, do we know always what it could be. If I drop a table and I depend on oid XXX, do I know if that is a type, function, or serial sequence? -- Bruce Momjian | http://candle.pha.pa.us pgman@candle.pha.pa.us | (610) 853-3000+ If your life is a hard drive, | 830 Blythe Avenue + Christ can be your backup. | Drexel Hill, Pennsylvania19026
> When a table is dropped, you scan all of these objects (their system > catalogs) for matches against the table and either do a cascade or > restrict. This is not new, we already do this for indexes and > descriptions, for instance. I was thinking we could centralize all that checking in pg_depend. However, we could decide just to do the areas where system tables don't work, like foreign keys and sequences. But when I find an oid depends on me, do I start scanning tables looking to see if is a sequence or a foreign key? -- Bruce Momjian | http://candle.pha.pa.us pgman@candle.pha.pa.us | (610) 853-3000+ If your life is a hard drive, | 830 Blythe Avenue + Christ can be your backup. | Drexel Hill, Pennsylvania19026
Bruce Momjian writes: > Is it? Are we going to record dependency both ways, e.g primary table > -> foreign table and foreign table -> primary table, or just one of > them. And when we see we depend on something, do we know always what it > could be. If I drop a table and I depend on oid XXX, do I know if that > is a type, function, or serial sequence? When you drop a table, there are only so many things that could depend on it: * rules/views * triggers * check constraints * foreign key constraints * primary key constraints * unique constraints * subtables including their dependencies. There might be others I forgot but a finite list can be defined. When a table is dropped, you scan all of these objects (their system catalogs) for matches against the table and either do a cascade or restrict. This is not new, we already do this for indexes and descriptions, for instance. -- Peter Eisentraut peter_e@gmx.net http://funkturm.homeip.net/~peter
Peter Eisentraut <peter_e@gmx.net> writes:
> Bruce Momjian writes:
>> But how then do you find the system table that uses the given oid?
> It's implied by the column you're looking at.
It is? Remember that we need to use this table to get from an object
to the objects that depend on it. A datatype OID, for example, would
have table OIDs (for column datatypes), function OIDs (for argument
datatypes), operator OIDs (ditto), aggregate OIDs (ditto), etc etc
dependent on it. How will you intuit which of those is represented
by a given row in pg_depend?
The alternative to pg_depend is to do a brute force scan of all the
system catalogs looking for dependent objects. In that case, you'd
know what you are looking at, but if we extract the dependencies as
a separate table, I don't see how you'd know without being told.
regards, tom lane
> When you drop a table, there are only so many things that could depend on > it: > > * rules/views > * triggers > * check constraints > * foreign key constraints > * primary key constraints > * unique constraints > * subtables > > including their dependencies. There might be others I forgot but a > finite list can be defined. > > When a table is dropped, you scan all of these objects (their system > catalogs) for matches against the table and either do a cascade or > restrict. This is not new, we already do this for indexes and > descriptions, for instance. Here is how I see it. If you use the pg_depend table to track these dependencies, you know at the time you do the insert where they come from so why not just record it at that time? Why poke around later looking at many system tables? The big issue is that you can pretty much centralize the stuff during INSERT and just use that on DROP/RENAME. I can even see a loop that says, "I am OK with sequence dependencies, but not other pg_class dependencies" or stuff like that. You can just trigger on the sysrelid in the table and determine where to go. If not you have to have all sorts of system poking code in DROP/RENAME, unless you want to just call a function to hit _every_ system table looking for the oid, which I doubt you want to do. -- Bruce Momjian | http://candle.pha.pa.us pgman@candle.pha.pa.us | (610) 853-3000+ If your life is a hard drive, | 830 Blythe Avenue + Christ can be your backup. | Drexel Hill, Pennsylvania19026
Tom Lane writes: > The alternative to pg_depend is to do a brute force scan of all the > system catalogs looking for dependent objects. In that case, you'd > know what you are looking at, but if we extract the dependencies as > a separate table, I don't see how you'd know without being told. The former is what I'm advocating. -- Peter Eisentraut peter_e@gmx.net http://funkturm.homeip.net/~peter
> Tom Lane writes: > > > The alternative to pg_depend is to do a brute force scan of all the > > system catalogs looking for dependent objects. In that case, you'd > > know what you are looking at, but if we extract the dependencies as > > a separate table, I don't see how you'd know without being told. > > The former is what I'm advocating. So you are basically saying you don't like pg_depend. Would you prefer to use it only in cases we can't encode the dependencies easily in the system catalogs, like functions that require certain relations? -- Bruce Momjian | http://candle.pha.pa.us pgman@candle.pha.pa.us | (610) 853-3000+ If your life is a hard drive, | 830 Blythe Avenue + Christ can be your backup. | Drexel Hill, Pennsylvania19026
Peter Eisentraut <peter_e@gmx.net> writes:
> Tom Lane writes:
>> The alternative to pg_depend is to do a brute force scan of all the
>> system catalogs looking for dependent objects. In that case, you'd
>> know what you are looking at, but if we extract the dependencies as
>> a separate table, I don't see how you'd know without being told.
> The former is what I'm advocating.
Seems like a bad idea; it'll slow down deletes quite a lot, no? Do you
really want to (for example) parse every SQL function in the system to
see if it refers to a table being dropped? Why would we want to do that
work over again for every such delete, rather than doing it once when
an object is created and storing the info in a table? Also consider
that what you are proposing is (at least) an O(N^2) algorithm when there
are a large number of objects.
Furthermore, a separate dependency table would allow us to support
user-defined dependencies. It could be that the user knows function A
should go away if table B does, yet there is no physical dependency that
the system would recognize for it.
regards, tom lane
On Tue, 17 Jul 2001, Peter Eisentraut wrote: > Tom Lane writes: > > > The alternative to pg_depend is to do a brute force scan of all the > > system catalogs looking for dependent objects. In that case, you'd > > know what you are looking at, but if we extract the dependencies as > > a separate table, I don't see how you'd know without being told. > > The former is what I'm advocating. Why? It's grossly inefficient and requires lots of effort. And scales horribly to adding new things which can depend on others. Following that argument (admittedly to an extreme conclusion), we should rip out index support. After all, all of the info in the index is stored in the table, we don't need to duplicate it elsewhere. pg_depend is a concise way to encode dependencies. We do all of the work at insert, where we know what depends on what. To not have pg_depend means that on delete, we have to scan EVERYTHING to see what depends on what we're dropping. If we find something (and are CASCADEing), we have to check and see if _it_ depends on anything (another complete scan). We have to keep doing complete scans until we find nothing. Take care, Bill
On Tue, 17 Jul 2001, Tom Lane wrote: > Seems like a bad idea; it'll slow down deletes quite a lot, no? Do you > really want to (for example) parse every SQL function in the system to > see if it refers to a table being dropped? Why would we want to do that > work over again for every such delete, rather than doing it once when > an object is created and storing the info in a table? Also consider > that what you are proposing is (at least) an O(N^2) algorithm when there > are a large number of objects. I think it's actually O(N^M) where there are N system objects and a chain of M dependencies (A depends on B which depends on C => M = 3). Take care, Bill
Bill Studenmund <wrstuden@zembu.com> writes:
> I think it's actually O(N^M) where there are N system objects and a chain
> of M dependencies (A depends on B which depends on C => M = 3).
It's probably not *that* bad. It's reasonable to assume that only a
small number of objects actually depend directly on any one object you
might want to delete. (Performance of deleting, say, the int4 datatype
is probably not of major interest ;-) ...) Only for those objects, not
for all N, would you need to descend to the next level of search.
Nonetheless, a properly indexed pg_depend table would allow you to find
these objects directly, and again to find their dependents directly,
etc. The brute force approach would require a rather expensive scan
over all the system catalogs, plus nontrivial analysis for some types
of system objects such as functions. Repeating that for each cascaded
delete is even less appetizing than doing it once.
regards, tom lane
On Tue, 17 Jul 2001, Tom Lane wrote: > Bill Studenmund <wrstuden@zembu.com> writes: > > I think it's actually O(N^M) where there are N system objects and a chain > > of M dependencies (A depends on B which depends on C => M = 3). > > It's probably not *that* bad. It's reasonable to assume that only a > small number of objects actually depend directly on any one object you > might want to delete. (Performance of deleting, say, the int4 datatype > is probably not of major interest ;-) ...) Only for those objects, not > for all N, would you need to descend to the next level of search. Ah yes. It'll be O(ND) where D is the number of dependers (the number of leaves in the dependency tree). > Nonetheless, a properly indexed pg_depend table would allow you to find > these objects directly, and again to find their dependents directly, > etc. The brute force approach would require a rather expensive scan > over all the system catalogs, plus nontrivial analysis for some types > of system objects such as functions. Repeating that for each cascaded > delete is even less appetizing than doing it once. Indeed. Take care, Bill
Peter Eisentraut wrote: > > Bruce Momjian writes: > > > > That was me. The point, however, was, given object id 145928, how the > > > heck to you know what table this comes from? > > > > I think we will need the relid of the system table. I imagine four > > columns: > > > > object relid > > object oid > > reference relid > > references oid > I like object relidobject oidobject namereference relidreference oid and unadorned DROP doesn't drop dependent objects. regards, Hiroshi Inoue
> I like > object relid > object oid > object name > reference relid > reference oid Can I ask why you like the object name? > > and unadorned DROP doesn't drop dependent objects. OK. -- Bruce Momjian | http://candle.pha.pa.us pgman@candle.pha.pa.us | (610) 853-3000+ If your life is a hard drive, | 830 Blythe Avenue + Christ can be your backup. | Drexel Hill, Pennsylvania19026
Bruce Momjian wrote: > > > I like > > object relid > > object oid > > object name > > reference relid > > reference oid > > Can I ask why you like the object name? > Oops I made a mistake. Reference name is needed not an object name, i.eobject relidobject oidrelerence relidreference oidreference name create table a (...);create view view_a as select .. from a; Then we have an pg_depend entry e.g. pg_class_relidoid of the view_apg_class_relidoid of the table a'a' the name of the table and so on. drop table a; (unadorned drop). Then the above entry would be changed to pg_class_relid(unchanged)oid of the view_s(unchagned)pg_class_relid(unchanged)InvalidOid'a' the name of the table(unchanged) create table a (...); Then the pg_depend entry would be pg_class_relid(unchanged)oid of the view_s(unchagned)pg_class_relid(unchanged)the oid of the new table a'a' the name of thetable(unchanged) regards, Hiroshi Inoue
> Then we have an pg_depend entry e.g. > > pg_class_relid > oid of the view_a > pg_class_relid > oid of the table a > 'a' the name of the table > > and so on. > > drop table a; (unadorned drop). > > Then the above entry would be changed to > > pg_class_relid(unchanged) > oid of the view_s(unchagned) > pg_class_relid(unchanged) > InvalidOid > 'a' the name of the table(unchanged) > > create table a (...); > > Then the pg_depend entry would be > > pg_class_relid(unchanged) > oid of the view_s(unchagned) > pg_class_relid(unchanged) > the oid of the new table a > 'a' the name of the table(unchanged) So you want to keep the name of the referenced object in case it is dropped. Makes sense. -- Bruce Momjian | http://candle.pha.pa.us pgman@candle.pha.pa.us | (610) 853-3000+ If your life is a hard drive, | 830 Blythe Avenue + Christ can be your backup. | Drexel Hill, Pennsylvania19026
At 11:25 18/07/01 +0900, Hiroshi Inoue wrote: > >Oops I made a mistake. >Reference name is needed not an object name, >i.e > object relid > object oid > relerence relid > reference oid > reference name > I think any deisgn needs to cater for attr dependencies. eg. create table a (f1 int4, f2 int8); create view view_a as select f2 from a; Then alter table a drop f1; -- Is OK. Should just happen alter table a drop f2; -- Should warn about the view, and/or cascadeetc. alter table a alter f2 float; -- Should trigger a view recompilation. ...same thing needs to happen with constraints that reference attrs I *think* tables are the only items that can have subobjects with dependant. ---------------------------------------------------------------- Philip Warner | __---_____ Albatross Consulting Pty. Ltd. |----/ - \ (A.B.N. 75 008 659 498) | /(@) ______---_ Tel: (+61) 0500 83 82 81 | _________ \ Fax: (+61) 0500 83 82 82 | ___________ | Http://www.rhyme.com.au | / \| | --________-- PGP key available upon request, | / and from pgp5.ai.mit.edu:11371 |/
On Tue, Jul 17, 2001 at 07:13:10PM -0400, Tom Lane wrote: > > Nonetheless, a properly indexed pg_depend table would allow you to find > these objects directly, and again to find their dependents directly, > etc. The brute force approach would require a rather expensive scan > over all the system catalogs, plus nontrivial analysis for some types > of system objects such as functions. Repeating that for each cascaded > delete is even less appetizing than doing it once. Stated that way, the performance argument sounds very convincing. However, the _real_ convincer for me is the support for user designated dependencies, as Tom pointed out earlier. That allows the system to do as much as possible automatically, (even functional dependency analysis, if someone want to write it) but doesn't require the automatic mechanisms to be perfect: the DBA has a mechanism to do the crazy, edge case things. Ross
> >Wouldn't that work simply by using the oid for the column in pg_attribute >as the primary dependency, rather than the table itself, from pg_class? So, >the dependency chain would be: > >view -> attribute -> table > >So your examples would 'just work', I think. > True. We need to remember to store both sets of dependencies (used attrs as well as the table dependency). ---------------------------------------------------------------- Philip Warner | __---_____ Albatross Consulting Pty. Ltd. |----/ - \ (A.B.N. 75 008 659 498) | /(@) ______---_ Tel: (+61) 0500 83 82 81 | _________ \ Fax: (+61) 0500 83 82 82 | ___________ | Http://www.rhyme.com.au | / \| | --________-- PGP key available upon request, | / and from pgp5.ai.mit.edu:11371 |/
On Wed, Jul 18, 2001 at 01:08:15PM +1000, Philip Warner wrote: > At 11:25 18/07/01 +0900, Hiroshi Inoue wrote: > > > >Oops I made a mistake. > >Reference name is needed not an object name, > >i.e > > object relid > > object oid > > relerence relid > > reference oid > > reference name > > > > I think any deisgn needs to cater for attr dependencies. eg. > > create table a (f1 int4, f2 int8); > create view view_a as select f2 from a; > > Then > > alter table a drop f1; -- Is OK. Should just happen > alter table a drop f2; -- Should warn about the view, and/or cascade etc. > alter table a alter f2 float; -- Should trigger a view recompilation. > > ...same thing needs to happen with constraints that reference attrs > > I *think* tables are the only items that can have subobjects with dependant. Wouldn't that work simply by using the oid for the column in pg_attribute as the primary dependency, rather than the table itself, from pg_class? So, the dependency chain would be: view -> attribute -> table So your examples would 'just work', I think. Ross
Philip Warner <pjw@rhyme.com.au> writes:
> At 11:38 18/07/01 -0400, Tom Lane wrote:
>> I'd just make the dependency be from view_a to a and keep things
>> simple. What's so wrong with recompiling the view for *every* change
>> of the underlying table?
> Not a problem for views, but when you get to constraints on large tables,
> re-evaluating all the constraints unnecessarily could be a nightmare, and
> especially frustrating when you just dropped an irrelevant attr.
Huh? You seem to be thinking that we'd need to re-check the constraint
at each row of the table, but I don't see why we'd need to. I was just
envisioning re-parsing the constraint source text.
regards, tom lane
> Philip Warner <pjw@rhyme.com.au> writes: > > I think any deisgn needs to cater for attr dependencies. eg. > > I don't really see a need to recognize dependencies at finer than table > level. I'd just make the dependency be from view_a to a and keep things > simple. What's so wrong with recompiling the view for *every* change > of the underlying table? What about other objects. Foreign keys? Serial? > We could support attr-level dependencies within the proposed pg_depend > layout if we made pg_attribute one of the allowed object categories. > However, I'd prefer not to make OID of pg_attribute rows be a primary > key for that table (in the long run I'd like to not assign OIDs at all > to pg_attribute, as well as other tables that don't need OIDs). So the > better way to do it would be to make the pg_depend entries include > attribute numbers. But I really think this is unnecessary complexity. I liked the pg_attribute references for some uses. I agree doing that for a view seems overly complex. I don't see any value in dropping oid from pg_attribute. -- Bruce Momjian | http://candle.pha.pa.us pgman@candle.pha.pa.us | (610) 853-3000+ If your life is a hard drive, | 830 Blythe Avenue + Christ can be your backup. | Drexel Hill, Pennsylvania19026
At 11:38 18/07/01 -0400, Tom Lane wrote: >Philip Warner <pjw@rhyme.com.au> writes: >> I think any deisgn needs to cater for attr dependencies. eg. > >I don't really see a need to recognize dependencies at finer than table >level. I'd just make the dependency be from view_a to a and keep things >simple. What's so wrong with recompiling the view for *every* change >of the underlying table? > Not a problem for views, but when you get to constraints on large tables, re-evaluating all the constraints unnecessarily could be a nightmare, and especially frustrating when you just dropped an irrelevant attr. ---------------------------------------------------------------- Philip Warner | __---_____ Albatross Consulting Pty. Ltd. |----/ - \ (A.B.N. 75 008 659 498) | /(@) ______---_ Tel: (+61) 0500 83 82 81 | _________ \ Fax: (+61) 0500 83 82 82 | ___________ | Http://www.rhyme.com.au | / \| | --________-- PGP key available upon request, | / and from pgp5.ai.mit.edu:11371 |/
> Hiroshi Inoue <Inoue@tpf.co.jp> writes: > > Reference name is needed not an object name, > > Only if we want to support the notion that drop-and-recreate-with-same-name > means that references from other objects should now apply to the new > object. I do not think that that's really a good idea, at least not > without a heck of a lot of compatibility checking. It'd be way too easy > to create cases where the properties of the new object do not match > what the referring object expects. > > The majority of the cases I've heard about where this would be useful > are for functions, and we could solve that a lot better with an ALTER > FUNCTION command that allows changing the function body (but not the > name, arguments, or result type). > > BTW, name alone is not a good enough referent for functions... you'd > have to store the argument types too. I assume the name was only for reference use so you could give the user an idea of what is missing. Clearly you don't use that to recreate anything, or I hope not. -- Bruce Momjian | http://candle.pha.pa.us pgman@candle.pha.pa.us | (610) 853-3000+ If your life is a hard drive, | 830 Blythe Avenue + Christ can be your backup. | Drexel Hill, Pennsylvania19026
Philip Warner <pjw@rhyme.com.au> writes:
> I think any deisgn needs to cater for attr dependencies. eg.
I don't really see a need to recognize dependencies at finer than table
level. I'd just make the dependency be from view_a to a and keep things
simple. What's so wrong with recompiling the view for *every* change
of the underlying table?
We could support attr-level dependencies within the proposed pg_depend
layout if we made pg_attribute one of the allowed object categories.
However, I'd prefer not to make OID of pg_attribute rows be a primary
key for that table (in the long run I'd like to not assign OIDs at all
to pg_attribute, as well as other tables that don't need OIDs). So the
better way to do it would be to make the pg_depend entries include
attribute numbers. But I really think this is unnecessary complexity.
regards, tom lane
Hiroshi Inoue <Inoue@tpf.co.jp> writes:
> Reference name is needed not an object name,
Only if we want to support the notion that drop-and-recreate-with-same-name
means that references from other objects should now apply to the new
object. I do not think that that's really a good idea, at least not
without a heck of a lot of compatibility checking. It'd be way too easy
to create cases where the properties of the new object do not match
what the referring object expects.
The majority of the cases I've heard about where this would be useful
are for functions, and we could solve that a lot better with an ALTER
FUNCTION command that allows changing the function body (but not the
name, arguments, or result type).
BTW, name alone is not a good enough referent for functions... you'd
have to store the argument types too.
regards, tom lane
> > > >Wouldn't that work simply by using the oid for the column in pg_attribute > >as the primary dependency, rather than the table itself, from pg_class? So, > >the dependency chain would be: > > > >view -> attribute -> table > > > >So your examples would 'just work', I think. > > > > True. We need to remember to store both sets of dependencies (used attrs as > well as the table dependency). TODO update with column labels: * Add pg_depend table for dependency recording; use sysrelid, oid, depend_sysrelid, depend_oid, name -- Bruce Momjian | http://candle.pha.pa.us pgman@candle.pha.pa.us | (610) 853-3000+ If your life is a hard drive, | 830 Blythe Avenue + Christ can be your backup. | Drexel Hill, Pennsylvania19026
On Wed, 18 Jul 2001, Hiroshi Inoue wrote: > Oops I made a mistake. > Reference name is needed not an object name, > i.e > object relid > object oid > relerence relid > reference oid > reference name > > create table a (...); > create view view_a as select .. from a; > > Then we have an pg_depend entry e.g. > > pg_class_relid > oid of the view_a > pg_class_relid > oid of the table a > 'a' the name of the table > > and so on. > > drop table a; (unadorned drop). > > Then the above entry would be changed to > > pg_class_relid(unchanged) > oid of the view_s(unchagned) > pg_class_relid(unchanged) > InvalidOid > 'a' the name of the table(unchanged) > > create table a (...); > > Then the pg_depend entry would be > > pg_class_relid(unchanged) > oid of the view_s(unchagned) > pg_class_relid(unchanged) > the oid of the new table a > 'a' the name of the table(unchanged) This step I disagree with. Well, I disagree with the automated aspect of the update. How does postgres know that the new table a is sufficiently like the old table that it should be used? A way the DBA could say, "yeah, restablish that," would be fine. Which is better, a view which is broken as the table it was based off of was dropped (even though there's a table of the same name now) or a view which is broken because there is now a table whose name matches its old table's name, but has different columns (either names or types)? I'd say #1. Take care, Bill
"Hiroshi Inoue" <Inoue@tpf.co.jp> writes:
>> BTW, name alone is not a good enough referent for functions... you'd
>> have to store the argument types too.
> ??? Isn't an entry
> pg_proc_relid
> the oid of the function
> pg_type_relid
> the oid of an argument type
> the name of the argument type
> made ?
That's the entry that was dropped, no? Given a pg_depend row pointing
at a function named foo, with an OID that no longer exists, how will you
tell which of the (possibly many) functions named foo is wanted?
regards, tom lane
Bruce Momjian <pgman@candle.pha.pa.us> writes:
> I don't see any value in dropping oid from pg_attribute.
Conservation of OIDs. Assigning an OID to every row of pg_attribute
chews up lots of OIDs, for a table that should never be referenced by
OID --- its primary key is (table OID, attribute number).
Right now this isn't really significant, but if/when we have an option
to suppress OID generation for user tables, I have every intention of
applying it to a bunch of the system tables as well. pg_attribute is
a prime candidate.
("When" probably means "next month", btw. This is on my 7.2 list...)
regards, tom lane
> -----Original Message----- > From: Tom Lane [mailto:tgl@sss.pgh.pa.us] > > Hiroshi Inoue <Inoue@tpf.co.jp> writes: > > Reference name is needed not an object name, > > Only if we want to support the notion that > drop-and-recreate-with-same-name > means that references from other objects should now apply to the new > object. I do not think that that's really a good idea, at least not > without a heck of a lot of compatibility checking. It'd be way too easy > to create cases where the properties of the new object do not match > what the referring object expects. > For example, we would process the following step to drop a column. select ....(all columns except a column) from a into b; drop table a; alter table b rename to a; But we would lose all relelvant objects. Though we may be able to solve this problem by implementing *drop column* properly, we couldn't solve this kind of problems at once. In fact neither *drop column* nor *cluster* is solved. We could always have (at least) the second best way by allowing drop-and-recreate-with-same-name revival. > The majority of the cases I've heard about where this would be useful > are for functions, and we could solve that a lot better with an ALTER > FUNCTION command that allows changing the function body (but not the > name, arguments, or result type). > > BTW, name alone is not a good enough referent for functions... you'd > have to store the argument types too. > ??? Isn't an entrypg_proc_relidthe oid of the functionpg_type_relidthe oid of an argument typethe name of the argument type made ? regards, Hiroshi Inoue
> Bruce Momjian <pgman@candle.pha.pa.us> writes:
> > I don't see any value in dropping oid from pg_attribute.
>
> Conservation of OIDs. Assigning an OID to every row of pg_attribute
> chews up lots of OIDs, for a table that should never be referenced by
> OID --- its primary key is (table OID, attribute number).
>
> Right now this isn't really significant, but if/when we have an option
> to suppress OID generation for user tables, I have every intention of
> applying it to a bunch of the system tables as well. pg_attribute is
> a prime candidate.
>
> ("When" probably means "next month", btw. This is on my 7.2 list...)
Yikes, I am not sure we are ready to make oids optional. System table
oid's seem like the last place to try and preserve oids. Do we return
unused oids back to the pool on backend exit yet? (I don't see it on
the TODO list.) That seems like a much more profitable place to start.
Will we have cheap 64-bit oids by the time oid wraparound becomes an
issue?
-- Bruce Momjian | http://candle.pha.pa.us pgman@candle.pha.pa.us | (610)
853-3000+ If your life is a hard drive, | 830 Blythe Avenue + Christ can be your backup. | Drexel Hill,
Pennsylvania19026
Bill Studenmund wrote: > > On Wed, 18 Jul 2001, Hiroshi Inoue wrote: > > > Oops I made a mistake. > > Reference name is needed not an object name, > > i.e > > object relid > > object oid > > relerence relid > > reference oid > > reference name > > > > create table a (...); > > create view view_a as select .. from a; > > > > Then we have an pg_depend entry e.g. > > > > pg_class_relid > > oid of the view_a > > pg_class_relid > > oid of the table a > > 'a' the name of the table > > > > and so on. > > > > drop table a; (unadorned drop). > > > > Then the above entry would be changed to > > > > pg_class_relid(unchanged) > > oid of the view_s(unchagned) > > pg_class_relid(unchanged) > > InvalidOid > > 'a' the name of the table(unchanged) > > > > create table a (...); > > > > Then the pg_depend entry would be > > > > pg_class_relid(unchanged) > > oid of the view_s(unchagned) > > pg_class_relid(unchanged) > > the oid of the new table a > > 'a' the name of the table(unchanged) > > This step I disagree with. Well, I disagree with the automated aspect of > the update. How does postgres know that the new table a is sufficiently > like the old table that it should be used? A way the DBA could say, "yeah, > restablish that," would be fine. > You could DROP a table with CASCADE or RESTRICT keyword if you hate the behavior. regards, Hiroshi Inoue
At 12:37 18/07/01 -0400, Tom Lane wrote: >Philip Warner <pjw@rhyme.com.au> writes: >> At 11:38 18/07/01 -0400, Tom Lane wrote: >>> I'd just make the dependency be from view_a to a and keep things >>> simple. What's so wrong with recompiling the view for *every* change >>> of the underlying table? > >> Not a problem for views, but when you get to constraints on large tables, >> re-evaluating all the constraints unnecessarily could be a nightmare, and >> especially frustrating when you just dropped an irrelevant attr. > >Huh? You seem to be thinking that we'd need to re-check the constraint >at each row of the table, but I don't see why we'd need to. I was just >envisioning re-parsing the constraint source text. I'm paranoid, but there could be a case for doing so, especially if we allow CHAR(n) to become CHAR(m) where m < n. Or any similar data-affecting field change. ---------------------------------------------------------------- Philip Warner | __---_____ Albatross Consulting Pty. Ltd. |----/ - \ (A.B.N. 75 008 659 498) | /(@) ______---_ Tel: (+61) 0500 83 82 81 | _________ \ Fax: (+61) 0500 83 82 82 | ___________ | Http://www.rhyme.com.au | / \| | --________-- PGP key available upon request, | / and from pgp5.ai.mit.edu:11371 |/
On Thu, 19 Jul 2001, Hiroshi Inoue wrote: > > This step I disagree with. Well, I disagree with the automated aspect of > > the update. How does postgres know that the new table a is sufficiently > > like the old table that it should be used? A way the DBA could say, "yeah, > > restablish that," would be fine. > > > > You could DROP a table with CASCADE or RESTRICT keyword if > you hate the behavior. You didn't answer the question. :-) "How does postgres know that the new table a is sufficiently like the old table that it should be used?" By making the reattachment automatic, you are saying that once we make an object of a given name and make objects depend on it, we can never have another object of the same name but different. Because PG is going to try to re-attach the dependants for you. That's different than current behavior, and strikes me as the system being overly helpful (a class of behavior I personally find very annoying). Please understand I like the idea of being ABLE to do this reattachment. I can see a lot of places where it would be VERY useful. My vote though is to just make reattachment a seperate step or something you flag, like in the CREATE TABLE, say attach me to everything wanting a table of this name. Make it something you have to indicate you want. Take care, Bill
Bill Studenmund wrote: > > On Thu, 19 Jul 2001, Hiroshi Inoue wrote: > > > > This step I disagree with. Well, I disagree with the automated aspect > of > > > the update. How does postgres know that the new table a is sufficiently > > > like the old table that it should be used? A way the DBA could say, "yeah, > > > restablish that," would be fine. > > > > > > > You could DROP a table with CASCADE or RESTRICT keyword if > > you hate the behavior. > > You didn't answer the question. :-) > > "How does postgres know that the new table a is sufficiently like the old > table that it should be used?" > > By making the reattachment automatic, you are saying that once we make an > object of a given name and make objects depend on it, we can never have > another object of the same name but different. Because PG is going to try > to re-attach the dependants for you. > > That's different than current behavior, and strikes me as the system being > overly helpful (a class of behavior I personally find very annoying). > > Please understand I like the idea of being ABLE to do this reattachment. I > can see a lot of places where it would be VERY useful. It doesn't seem preferable that the default(unadorned) DROP allows reattachement after the DROP. The default(unadorned) DROP should be the same as DROP RESTRICT(or CASCADE because the current behabior is halfway CASCADE?). How about adding another keyword to allow reattachment after the DROP ? All depende(a?)nt objects must be re-complied after the reattachment and the re-compilation would fail if the new table isn't sufficiently like the old one. Anyway my opinion seems in a minority as usual. regards, Hiroshi Inoue
On Fri, Jul 20, 2001 at 08:45:05AM +0900, Hiroshi Inoue wrote: > > It doesn't seem preferable that the default(unadorned) DROP > allows reattachement after the DROP. The default(unadorned) DROP > should be the same as DROP RESTRICT(or CASCADE because the current > behabior is halfway CASCADE?). How about adding another keyword > to allow reattachment after the DROP ? > All depende(a?)nt objects must be re-complied after the > reattachment and the re-compilation would fail if the new table > isn't sufficiently like the old one. > > Anyway my opinion seems in a minority as usual. > How about making that functionality happen with ALTER <FOO> REPLACE as Tom suggested? If I'm wanting to change an underlying table, how likely is it that I don't have the replacement ready right now? So, instead of: DROP <FOO> <name> WITH INTENT TO REPLACE CREATE <FOO> <name> <body> it's just: ALTER <FOO> <name> REPLACE <body> All nice and transactional: if the attempt to reattach one of the subordinate objects fails, you roll back to the old one. Ross
On Fri, 20 Jul 2001, Hiroshi Inoue wrote: > Bill Studenmund wrote: > > > > "How does postgres know that the new table a is sufficiently like the old > > table that it should be used?" > > > > By making the reattachment automatic, you are saying that once we make an > > object of a given name and make objects depend on it, we can never have > > another object of the same name but different. Because PG is going to try > > to re-attach the dependants for you. > > > > That's different than current behavior, and strikes me as the system being > > overly helpful (a class of behavior I personally find very annoying). > > > > Please understand I like the idea of being ABLE to do this reattachment. I > > can see a lot of places where it would be VERY useful. > > It doesn't seem preferable that the default(unadorned) DROP > allows reattachement after the DROP. The default(unadorned) DROP > should be the same as DROP RESTRICT(or CASCADE because the current > behabior is halfway CASCADE?). How about adding another keyword > to allow reattachment after the DROP ? Hmmm... My preference is for the subsequent CREATE to indicate if reattach should happen or not. But I'm not sure if that would leave dangling depend entries around. > All depende(a?)nt objects must be re-complied after the > reattachment and the re-compilation would fail if the new table > isn't sufficiently like the old one. > > Anyway my opinion seems in a minority as usual. Only partly. I think everyone likes the idea of being able to reattach later, an idea you came up with. :-) Take care, Bill