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74dfe58a59
For a long time, indxpath.c has had the ability to extract derived (lossy) index conditions from certain operators such as LIKE. For just as long, it's been obvious that we really ought to make that capability available to extensions. This commit finally accomplishes that, by adding another API for planner support functions that lets them create derived index conditions for their functions. As proof of concept, the hardwired "special index operator" code formerly present in indxpath.c is pushed out to planner support functions attached to LIKE and other relevant operators. A weak spot in this design is that an extension needs to know OIDs for the operators, datatypes, and opfamilies involved in the transformation it wants to make. The core-code prototypes use hard-wired OID references but extensions don't have that option for their own operators etc. It's usually possible to look up the required info, but that may be slow and inconvenient. However, improving that situation is a separate task. I want to do some additional refactorization around selfuncs.c, but that also seems like a separate task. Discussion: https://postgr.es/m/15193.1548028093@sss.pgh.pa.us
58 lines
2.5 KiB
C
58 lines
2.5 KiB
C
/*-------------------------------------------------------------------------
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*
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* catversion.h
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* "Catalog version number" for PostgreSQL.
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*
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* The catalog version number is used to flag incompatible changes in
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* the PostgreSQL system catalogs. Whenever anyone changes the format of
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* a system catalog relation, or adds, deletes, or modifies standard
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* catalog entries in such a way that an updated backend wouldn't work
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* with an old database (or vice versa), the catalog version number
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* should be changed. The version number stored in pg_control by initdb
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* is checked against the version number compiled into the backend at
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* startup time, so that a backend can refuse to run in an incompatible
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* database.
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*
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* The point of this feature is to provide a finer grain of compatibility
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* checking than is possible from looking at the major version number
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* stored in PG_VERSION. It shouldn't matter to end users, but during
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* development cycles we usually make quite a few incompatible changes
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* to the contents of the system catalogs, and we don't want to bump the
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* major version number for each one. What we can do instead is bump
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* this internal version number. This should save some grief for
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* developers who might otherwise waste time tracking down "bugs" that
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* are really just code-vs-database incompatibilities.
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*
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* The rule for developers is: if you commit a change that requires
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* an initdb, you should update the catalog version number (as well as
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* notifying the pghackers mailing list, which has been the informal
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* practice for a long time).
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*
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* The catalog version number is placed here since modifying files in
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* include/catalog is the most common kind of initdb-forcing change.
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* But it could be used to protect any kind of incompatible change in
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* database contents or layout, such as altering tuple headers.
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*
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*
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* Portions Copyright (c) 1996-2019, PostgreSQL Global Development Group
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* Portions Copyright (c) 1994, Regents of the University of California
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*
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* src/include/catalog/catversion.h
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*
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*-------------------------------------------------------------------------
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*/
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#ifndef CATVERSION_H
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#define CATVERSION_H
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/*
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* We could use anything we wanted for version numbers, but I recommend
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* following the "YYYYMMDDN" style often used for DNS zone serial numbers.
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* YYYYMMDD are the date of the change, and N is the number of the change
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* on that day. (Hopefully we'll never commit ten independent sets of
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* catalog changes on the same day...)
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*/
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/* yyyymmddN */
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#define CATALOG_VERSION_NO 201902112
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#endif
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