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Since hash indexes typically have very few overflow pages, adding a new splitpoint essentially doubles the on-disk size of the index, which can lead to large and abrupt increases in disk usage (and perhaps long delays on occasion). To mitigate this problem to some degree, divide larger splitpoints into four equal phases. This means that, for example, instead of growing from 4GB to 8GB all at once, a hash index will now grow from 4GB to 5GB to 6GB to 7GB to 8GB, which is perhaps still not as smooth as we'd like but certainly an improvement. This changes the on-disk format of the metapage, so bump HASH_VERSION from 2 to 3. This will force a REINDEX of all existing hash indexes, but that's probably a good idea anyway. First, hash indexes from pre-10 versions of PostgreSQL could easily be corrupted, and we don't want to confuse corruption carried over from an older release with any corruption caused despite the new write-ahead logging in v10. Second, it will let us remove some backward-compatibility code added by commit 293e24e507838733aba4748b514536af2d39d7f2. Mithun Cy, reviewed by Amit Kapila, Jesper Pedersen and me. Regression test outputs updated by me. Discussion: http://postgr.es/m/CAD__OuhG6F1gQLCgMQNnMNgoCvOLQZz9zKYJQNYvYmmJoM42gA@mail.gmail.com Discussion: http://postgr.es/m/CA+TgmoYty0jCf-pa+m+vYUJ716+AxM7nv_syvyanyf5O-L_i2A@mail.gmail.com
The PostgreSQL contrib tree
---------------------------
This subtree contains porting tools, analysis utilities, and plug-in
features that are not part of the core PostgreSQL system, mainly
because they address a limited audience or are too experimental to be
part of the main source tree. This does not preclude their
usefulness.
User documentation for each module appears in the main SGML
documentation.
When building from the source distribution, these modules are not
built automatically, unless you build the "world" target. You can
also build and install them all by running "make all" and "make
install" in this directory; or to build and install just one selected
module, do the same in that module's subdirectory.
Some directories supply new user-defined functions, operators, or
types. To make use of one of these modules, after you have installed
the code you need to register the new SQL objects in the database
system by executing a CREATE EXTENSION command. In a fresh database,
you can simply do
CREATE EXTENSION module_name;
See the PostgreSQL documentation for more information about this
procedure.