The attached patch is revised one based on the V3 approach.
The only difference from V3 is that it also applies checks on the
AT_AlterColumnType option, not only renameatt().
The performance was almost same as the V3 case.
> * CVS HEAD
- ALTER RENAME TO with V5 patch
I also checked ALTER ... TYPE cases. It is relatively heavy operation than
renameatt(), so its affects was relatively smaller.
- ALTER ... TYPE with CVS HEAD
- ALTER ... TYPE with V5 patch
(2010/01/26 10:10), KaiGai Kohei wrote:
> (2010/01/26 1:11), Bernd Helmle wrote:
>> --On 25. Januar 2010 11:39:21 +0900 KaiGai Kohei<kaigai(at)ak(dot)jp(dot)nec(dot)com>
>>> (echo "CREATE TABLE t (a int);"
>>> for i in `seq 0 9`; do
>>> echo "CREATE TABLE s$i (b int) INHERITS(t);"
>>> for j in `seq 0 9`; do
>>> echo "CREATE TABLE v$i$j (c int) INHERITS(s$i);"
>>> for k in `seq 0 9`; do
>>> echo "CREATE TABLE w$i$j$k (d int) INHERITS(v$i$j);"
>>> for l in `seq 0 9`; do
>>> echo "CREATE TABLE x$i$j$k$l (e int) INHERITS(w$i$j$k);"
>>> done) | psql test
>> Well, each table inherits one table in your test. In my test, I inherit
>> from multiple tables for each table. My script generates the following
>> inheritance tree (and wins a price of copy& paste ugliness, see
>> A1, A2, A3, ..., Am
>> B1 INHERITS(A1...A10), B2 INHERITS(A1...A10, B3 INHERITS(A1...A10), ...Bn
>> C1 INHERITS(B1...B10), C2 INHERITS(B1...B10), ... Co
>> D1 INHERITS(C1...C10), ..., Dp
>> m = 10
>> n = 10
>> o = 10
>> p = 1000
>> Repeating this on my MacBook gives:
>> ALTER TABLE a1 RENAME COLUMN acol1 TO xyz;
>> Time: 382,427 ms
>> Time: 375,974 ms
>> Time: 385,478 ms
>> Time: 371,067 ms
>> Time: 410,834 ms
>> Time: 386,382 ms
>> Recent V4 patch:
>> Time: 6065,673 ms
>> Time: 3823,206 ms
>> Time: 4037,933 ms
>> Time: 3873,029 ms
>> Time: 3899,607 ms
>> Time: 3963,308 ms
> Hmm... I also could observe similar result in 4 times iteration of
> ALTER TABLE with your test_rename.sql.
> I agree the recent V4 patch is poor in performance perspective.
> * CVS HEAD
> * Rcent V4 patch:
> * Previous V3 patch:
> The V3 patch is designed to compute an expected inhcount for each relations
> to be altered at first, then it shall be compared to pg_attribute.inhcount
> to be renamed.
> Basically, its execution cost is same order except for a case when a relation
> has diamond inheritance tree.
> The find_all_inheritors() does not check child relations which is already
> scanned. However, in this case, we have to check how many times is the child
> relation inherited from a common origin.
> I guess it is reason of the different between -HEAD and V3.
> For example, if we have the following inheritance tree,
> A2 A5
> / \ \
> A1 A4
> \ / \
> A3 -- A6
> The find_all_inheritors() checks existence of directly inherited relations
> at A1, ... , A6 without any duplications, because this function does not
> intend to compute how many times was it inherited.
> The find_all_inheritors_with_inhcount() in V3 patch checks existence of
> directly inherited relations, even if the target relation is already checked,
> because it also has to return the times to be inherited from a common origin.
> In this example, it considers the above structure is same as the following
> tree. In this diagram, we can find A4 and A5 twice, and A6 thrice.
> A2 - A4 - A6
> A3 - A4 - A6
> \ \
> A6 A5
> Thus, the test_rename.sql was the worst case test for V3 also.
> However, I don't think we should keep the bug in the next release.
> The CVS HEAD's performance is the result of omission for necessary checks.
> I think we should back to the V3 patch approach, and also reconsider
> the logic in ATPrepAlterColumnType().
OSS Platform Development Division, NEC
KaiGai Kohei <kaigai(at)ak(dot)jp(dot)nec(dot)com>
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