On 10/31/2014 04:14 PM, Mark Woodward wrote:
I have not kept up with PostgreSQL changes and have just been using it. A
co-worker recently told me that you need to word "CONCURRENTLY" in "CREATE
INDEX" to avoid table locking. I called BS on this because to my knowledge
PostgreSQL does not lock tables. I referenced this page in the
documentation:
http://www.postgresql.org/docs/9.3/static/locking-indexes.html
Wrong list? This has nothing to do with pgadmin...
However, I do see this sentece in the indexing page that was not in the
docs prior to 8.0:
"Creating an index can interfere with regular operation of a database.
Normally PostgreSQL locks the table to be indexed against writes and
performs the entire index build with a single scan of the table."
Is this true? When/why the change?
Plain CREATE INDEX has always locked the table. You can query it while
the CREATE INDEX is running, but updates will block.
CREATE INDEX CONCURRENTLY was a new feature in 8.2 that avoids taking
that lock, allowing concurrent updates. It's slower than the
non-concurrent version, because it has to scan the table twice, and
there are a few other caveats. See
http://www.postgresql.org/docs/9.4/static/sql-createindex.html#SQL-CREATEINDEX-CONCURRENTLY.
- Heikki
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