diff --git a/doc/src/sgml/indices.sgml b/doc/src/sgml/indices.sgml index 17630c586d..d060d044de 100644 --- a/doc/src/sgml/indices.sgml +++ b/doc/src/sgml/indices.sgml @@ -1,4 +1,4 @@ - + Indexes @@ -93,8 +93,9 @@ CREATE INDEX test1_id_index ON test1 (id); Creating an index on a large table can take a long time. By default, PostgreSQL allows reads (selects) to occur - on the table in parallel with index creation, but writes (inserts, + on the table in parallel with creation of an index, but writes (inserts, updates, deletes) are blocked until the index build is finished. + In production environments this is often unacceptable. It is possible to allow writes to occur in parallel with index creation, but there are several caveats to be aware of — for more information see @@ -264,22 +264,19 @@ CREATE [ UNIQUE ] INDEX [ CONCURRENTLY ] name - Creating an index for a large table can be a long operation. In large data - warehousing applications it can easily take hours or even days to build - indexes. It's important to understand the impact creating indexes has on a - system. - - - + 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. Other transactions can still read the table, but if they try to insert, update, or delete rows in the table they will block until the - index build is finished. + index build is finished. This could have a severe effect if the system is + a live production database. Large tables can take many hours to be + indexed, and even for smaller tables, an index build can lock out writers + for periods that are unacceptably long for a production system. - PostgreSQL also supports building indexes without locking + PostgreSQL supports building indexes without locking out writes. This method is invoked by specifying the CONCURRENTLY option of CREATE INDEX. When this option is used,