Tag: alter table

How to run short ALTER TABLE without long locking concurrent queries

Recently I've seen case like:

  1. application had to add column to table.
  2. application ran ALTER TABLE ADD COLUMN (without default!)
  3. everything stopped for many MINUTES

Why? How to avoid the problem?

Continue reading How to run short ALTER TABLE without long locking concurrent queries

Waiting for 9.6 – Add IF NOT EXISTS processing to ALTER TABLE ADD COLUMN

On 30th of July, Andrew Dunstan committed patch:

Add IF NOT EXISTS processing to ALTER TABLE ADD COLUMN
 
Fabrízio de Royes Mello, reviewed by Payal Singh, Alvaro Herrera and
Michael Paquier.

Continue reading Waiting for 9.6 – Add IF NOT EXISTS processing to ALTER TABLE ADD COLUMN

Waiting for 9.5 – Event Trigger for table_rewrite

On 7th of December, Simon Riggs committed patch:

Event Trigger for table_rewrite
 
Generate a table_rewrite event when ALTER TABLE
attempts to rewrite a table. Provide helper
functions to identify table and reason.
 
Intended use case is to help assess or to react
to schema changes that might hold exclusive locks
for long periods.
 
Dimitri Fontaine, triggering an edit by Simon Riggs
 
Reviewed in detail by Michael Paquier

Continue reading Waiting for 9.5 – Event Trigger for table_rewrite

Waiting for 9.5 – Implement ALTER TABLE .. SET LOGGED / UNLOGGED

On 22nd of August, Alvaro Herrera committed patch:

Implement ALTER TABLE .. SET LOGGED / UNLOGGED
 
This enables changing permanent (logged) tables to unlogged and
vice-versa.
 
(Docs for ALTER TABLE / SET TABLESPACE got shuffled in an order that
hopefully makes more sense than the original.)
 
Author: Fabrízio de Royes Mello
Reviewed by: Christoph Berg, Andres Freund, Thom Brown
Some tweaking by Álvaro Herrera

Continue reading Waiting for 9.5 – Implement ALTER TABLE .. SET LOGGED / UNLOGGED

Waiting for 9.2 – More rewrite-less ALTER TABLE ALTER TYPEs

Three patches for you today, all committed by Robert Hass:

  • On 7th of February, patch: 
    Add a transform function for numeric typmod coercisions.
 
This enables ALTER TABLE to skip table and index rebuilds when a column
is changed to an unconstrained numeric, or when the scale is unchanged
and the precision does not decrease.
 
Noah Misch, with a few stylistic changes and a fix for an OID
collision by me.
  • also on 7th, patch: 
    Add a transform function for varbit typmod coercisions.
 
This enables ALTER TABLE to skip table and index rebuilds when the
new type is unconstraint varbit, or when the allowable number of bits
is not decreasing.
 
Noah Misch, with review and a fix for an OID collision by me.
  • and a day later final patch: 
    Add transform functions for various temporal typmod coercisions.
 
This enables ALTER TABLE to skip table and index rebuilds in some cases.
 
Noah Misch, with trivial changes by me.

Continue reading Waiting for 9.2 – More rewrite-less ALTER TABLE ALTER TYPEs

Waiting for 9.2 – Avoiding reindexing on alter type of indexed column

On 18th of July, Robert Haas committed patch:

Avoid index rebuild for no-rewrite ALTER TABLE .. ALTER TYPE.
 
Noah Misch.  Review and minor cosmetic changes by me.

Continue reading Waiting for 9.2 – Avoiding reindexing on alter type of indexed column

Waiting for 9.1 – Rewrite-less changing types of column

On 12th of February, Robert Haas committed patch:

Teach ALTER TABLE .. SET DATA TYPE TO avoid SOME TABLE rewrites.
 
WHEN the OLD TYPE IS BINARY coercible TO the NEW TYPE AND the USING     
clause does NOT CHANGE the COLUMN contents, we can avoid a FULL TABLE
rewrite, though any indexes ON the affected COLUMNS will still need
TO be rebuilt.  This applies, FOR example, WHEN changing a VARCHAR
COLUMN TO be OF TYPE text.
 
The prior coding assumed that the SET OF operations that force a
rewrite IS identical TO the SET OF operations that must be propagated
TO TABLES making USE OF the affected TABLE's rowtype.  This is
no longer true: even though the tuples in those tables wouldn't
need TO be modified, the DATA TYPE CHANGE invalidate indexes built
USING those composite TYPE COLUMNS.  Indexes ON the TABLE we're
actually modifying can be invalidated too, of course, but the
existing machinery is sufficient to handle that case.
 
Along the way, add some debugging messages that make it possible
to understand what operations ALTER TABLE is actually performing
in these cases.                                                      
 
Noah Misch and Robert Haas

Later on, on 15th, he committed second patch with few more cases where rewrite can be avoided.

Continue reading Waiting for 9.1 – Rewrite-less changing types of column

Waiting for 9.1 – Reduced lock levels for ALTER TABLE

On 28th of July, Simon Riggs committed patch which:

Log Message:
-----------
Reduce LOCK levels OF CREATE TRIGGER AND SOME ALTER TABLE, CREATE RULE actions.
Avoid hard-coding lockmode used FOR many altering DDL commands, allowing easier
future changes OF LOCK levels. Implementation OF initial analysis ON DDL
sub-commands, so that many LOCK levels are now at ShareUpdateExclusiveLock OR
ShareRowExclusiveLock, allowing certain DDL NOT TO block reads/writes.
FIRST OF NUMBER OF planned changes IN this area; additional docs required
WHEN FULL project complete.

Continue reading Waiting for 9.1 – Reduced lock levels for ALTER TABLE