|From:||Nikolay Shaplov <dhyan(at)nataraj(dot)su>|
|Cc:||Alvaro Herrera <alvherre(at)2ndquadrant(dot)com>|
|Subject:||Re: [PATCH] Move all am-related reloption code into src/backend/access/[am-name] and get rid of relopt_kind for custom AM|
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I've rebased the patch again.
Alvaro, I am waiting for you! ;-)
> I've rebased the patch, so it can be applied to current master. See
> Alvaro in private letter told that he will review the patch some time later.
> So I am waiting.
> Also added this patch to commitfest:
> > (Please see Attribution notice at the bottom of the letter)
> > Hi! Some time ago I've send a proposal, about removing all am-related code
> > from src/backend/access/common/reloptions.c and move it into somewhere
> > inside am code. It was in
> > https://www.postgresql.org/message-id/4636505.Bu9AKW1Kzc%40nataraj-amd64
> > thread.
> > Now I have a patch that is ready
> > Before explaining what have been done, I need to define some concepts, so
> > it would be easy to speak about them in the further explanation.
> > Reloptions values in postgres actually exists in four representations:
> > DefList*, TextArray, Bytea and so called Values.
> > - DefList representation is a list of DefElem, it is the representation in
> > which reloptions comes from syntax analyzer, when relation is created or
> > altered, and also this representation that is needed for pg_dump to dump a
> > create statement that creates this relation.
> > - TextArray representation is a way, how reloptions are stored in
> > pg_catalog. It is TEXT attribute in the pg_catalog table and from the
> > poinf o view of postgres code it is Datum array of TEXT Datums, when read
> > into the memory
> > - Bytea (or I will also call it Binary) representation, is a
> > representation with which relation code really works. It has C-structure
> > inside in which fixed-length options are sored, some space is reserved
> > for storing varlen values after the structure, and certainly it has BYTEA
> > header in front of all of it. It is cached, it is fast to access. It is a
> > good stuff.
> > - Values (or in some cases RawValues) -- internal representation of option
> > parser. Technically it is List of option_value structures (old name for it
> > is relopt_value). This representation is used for parsing and validating
> > options. Actually all the convertations between representations listed
> > above are dove through Values representation. Values are called RawValues
> > when Values List were already created, but it was not parsed yet, and all
> > option values are in raw state: represented as a text.
> > DefList and TextArray representations are converted in both ways(always
> > through Values representation): we need DefList -> TextArray to create or
> > change entry in the pg_catalog, and need TextArray -> DefList for pg_dump
> > Bytea representation is converted from TextArray representation (also
> > through Values representation). When relation code, tries to get cached
> > Bytea representation for certain relation, and none is actually cached,
> > then cache code calls extractRelOptions function that fetches entry from
> > pg_catalog for that relation, gets reloptions TextArray, converts it
> > into Bytea and cache it.
> > Each reloption has it's own definition. This definitions tells how this
> > option should be parsed, validated and converted. Before my patch this
> > information were stored in relopt_gen and relopt_parse_elt structures. In
> > my patch all this information were moved into option_definition_basic
> > structure (that is actually old relopt_gen + relopt_parse_elt)
> > The set of options definition I would call a options catalog. Before my
> > patch there was one global options catalog (actually it was divided into
> > parts by data types and has another part for dynamically added options,
> > but
> > nevertheless, it was global). After my patch there would be a separate
> > options catalog for each relation type. For AM-relation this catalog would
> > be available via AM-handler. for other relation types it would be still
> > kept in reloption.c
> > Now I am ready to tell what actually have been done in this patch:
> > 1. I moved options definitions from global lists from reloptions.c
> > [type name]RelOpts to lists that are kept inside AM code. One list per AM.
> > heap options, toast options and options for all other relation types that
> > are not accessible through AccessMethod, all were kept inside
> > reloptions.c, but now it is one list for each relation type, not a global
> > one
> > 2. Each AccessMethod had amoptions function that was responsible for
> > converting reloptions from TextArray representation into Bytea
> > representaions. This function used functions from reloptions.c and also
> > had
> > an array of relopt_parse_elt that defines how parsed reloption data should
> > be packed inside Bytea chunk. I've moved data from relopt_parse_elt array
> > into option definitions that are stored in the catalog (since catalog are
> > now defined inside the AccessMethod we have access to a structure of Bytea
> > representation at the place where we define option catalog)
> > 3. Speaking of amoptions function, I've completely removed it, since we do
> > not need it. For developers of Access Methods who still want to do some
> > custom action with just parsed data, I've added postprocess_fun to option
> > catalog. If this function is defined, it is called by convertation
> > function
> > right after Bytea representation were created. In postprocess_fun
> > developer
> > can do some custom validation, or change just parsed data. This feature is
> > used in bloom index.
> > 4. Instead of amoptions function I've added amrelopt_catalog function to
> > the Access Method. This function returns option definition catalog for an
> > Access Method. The catalog is used for processing options.
> > 5. As before, relation cache calls extractRelOptions when it needs options
> > that were not previously cached.
> > Before my patch, it created Bytea representations for non-AM relations,
> > and
> > called amoptions AM function to get Bytea representation for AM relation.
> > In by patch, it now gets option catalog, (using local functions for non-AM
> > relations, and using amrelopt_catalog function for AM-relations), and
> > then
> > use this catalog to convert options from TextArray into Bytea
> > representation.
> > 6. I've added some more featues:
> > - Now you can set OPTION_DEFINITION_FLAG_FORBID_ALTER flag in definition
> > of
> > the option, and then postgres will refuse to change option value using
> > ALTER command. In many indexes, some options are used only for index
> > creation. After this it's value is saved in MetaPage, and used from there.
> > Nevertheless user is allowed to change option value, though it affects
> > nothing, one need to recreate index to really change such value. Now using
> > this flag we can prevent user from getting an illusion that he
> > successfully
> > changed option value.
> > - After applying my patch if you try to set toast. option for table that
> > does not have toast, you will get an error. Before postgres will accept
> > toast option for a table without a toast, but this value will be lost.
> > This
> > is bad behavior, so now postgres will throw an error in this case.
> > - I've noticed that all string relation options in postgres are
> > technically
> > enum options. So I've added enum option type. This will save some bytes of
> > the memory and some tacts of the CPU. I also left string option type
> > (through it is not used now). A. Korotkov said that it might be needed
> > later for storing patterns, xml/json paths or something like that.
> > - Added some more tests that will trigger more options code. Though I am
> > dreaming about more advanced test system, that will allow to check that
> > certain value is received somewhere deep in the code.
> > 7. And now the most controversial change. I've got rid of StdRdOptions
> > structure, in which options for heap, toast, nbtree, hash and spgist were
> > stored in Bytea representation. In indexes only fillfactor value were
> > actually used from the whole big structure. So I've created a separate
> > structure for each relation type. HeapOptions and ToastOptions are very
> > similar to each other. So common part of creating these catalogs were
> > moved
> > to
> > add_autovacuum_options function that are called while creating each
> > catalog.
> > Now to the controversial part: in src/include/utils/rel.h had a lot of
> > Relation* macroses that used StdRdOptions structure. I've changed them
> > into
> > View* Heap* and Toast* analogues, and changed the code to use these
> > macroses instead of Relation* one. But this part of code I least sure of.
> > I'd like to ask experienced developers to double check it.
> > 8. I've moved all options-abstract code into options.c and options.h file,
> > and left in reloptions.c and reloptions.h only the code that concerns
> > relation options. Actually the main idea of this patch was to get this
> > abstract code in order to use it for custom attribute options later. All
> > the rest just a side effects :-)
> > So, before adding this to commitfest I want somebody to give a general
> > look
> > at it, if the code is OK.
> > Alvaro Herrera, you once said that you can review the patch...
> > The patch is available in the attachment. It can be applied to current
> > master
> > You can also see latest version on my github
> > https://github.com/dhyannataraj/postgres/tree/reloption_fix
> > at the reloption_fix branch.
> > ATTRIBUTION NOTICE: I wrote this patch, when I was an employee in
> > Postgres
> > Professional company. So this patch should be attributed as patch from
> > Postgres Pro (or something like that). For some reasons I did not manage
> > to
> > commit this patch while I left that job. But I got a permission to commit
> > it even if I left the company.
> > So my contribution to this patch as a independent developer was final code
> > cleanup, and writing some more comments. All the rest was a work of
> > Postgres Pro employee Nikolay Shaplov.
Nikolay Shaplov, independent Perl & C/C++ developer. Available for hire.
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