Add to TODO.detail.

doc/TODO.detail/drop

@@ -2,7 +2,7 @@ From pgsql-hackers-owner+M3040@hub.org Thu Jun  8 00:31:01 2000
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@@ -411,7 +411,7 @@ From tgl@sss.pgh.pa.us Sat Jun 10 01:31:04 2000
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@@ -457,7 +457,7 @@ From dhogaza@pacifier.com Sat Jun 10 09:30:59 2000
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@@ -509,7 +509,7 @@ From tgl@sss.pgh.pa.us Sun Jun 11 12:31:03 2000
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@@ -778,3 +778,64 @@ jdavis@dynworks.com
 http://dynworks.com
 
 
+From owner-pgsql-hackers@hub.org Sat Feb 26 01:07:45 2000
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+To: Bruce Momjian <pgman@candle.pha.pa.us>
+cc: Peter Eisentraut <peter_e@gmx.net>,
+        PostgreSQL Development <pgsql-hackers@postgreSQL.org>
+Subject: Re: [HACKERS] ALTER TABLE DROP COLUMN 
+In-reply-to: <200002260412.XAA14752@candle.pha.pa.us> 
+References: <200002260412.XAA14752@candle.pha.pa.us>
+Comments: In-reply-to Bruce Momjian <pgman@candle.pha.pa.us>
+	message dated "Fri, 25 Feb 2000 23:12:26 -0500"
+Date: Sat, 26 Feb 2000 01:01:33 -0500
+Message-ID: <14225.951544893@sss.pgh.pa.us>
+From: Tom Lane <tgl@sss.pgh.pa.us>
+Sender: owner-pgsql-hackers@postgreSQL.org
+Status: ORr
+
+Bruce Momjian <pgman@candle.pha.pa.us> writes:
+> You can exclusively lock the table, then do a heap_getnext() scan over
+> the entire table, remove the dropped column, do a heap_insert(), then a
+> heap_delete() on the current tuple, making sure to skip over the tuples
+> inserted by the current transaction.  When completed, remove the column
+> from pg_attribute, mark the transaction as committed (if desired), and
+> run vacuum over the table to remove the deleted rows.
+
+Hmm, that would work --- the new tuples commit at the same instant that
+the schema updates commit, so it should be correct.  You have the 2x
+disk usage problem, but there's no way around that without losing
+rollback ability.
+
+A potentially tricky bit will be persuading the tuple-reading and tuple-
+writing subroutines to pay attention to different versions of the tuple
+structure for the same table.  I haven't looked to see if this will be
+difficult or not.  If you can pass the TupleDesc explicitly then it
+shouldn't be a problem.
+
+I'd suggest that the cleanup vacuum *not* be an automatic part of
+the operation; just recommend that people do it ASAP after dropping
+a column.  Consider needing to drop several columns...
+
+			regards, tom lane
+
+************
+