Re: Call flow of btinsert(PG_FUNCTION_ARGS)

On Tue, Nov 19, 2013 at 11:52 AM, Craig Ringer <craig(at)2ndquadrant(dot)com>wrote:

> On 11/19/2013 06:22 PM, Rohit Goyal wrote:
> > Hi All,
> >
> > I was reading b tree index code and I wanted to the know the calling
> > function which calls btinsert
> > <
> http://doxygen.postgresql.org/nbtree_8c.html#a2b69e4abd6e38fbb317a503b8cf6e00a
> >(PG_FUNCTION_ARGS
> > <
> http://doxygen.postgresql.org/fmgr_8h.html#adf4dec9b7d23f1b4c68477affde8b7ff
> >)
> > function in nbtree.c file.
>
> It's specified as a member of the btree index access method in
> include/catalog/pg_am.h . All invocations are done via index access
> method lookups; see the documentation for pg_catalog.pg_am, index access
> methods, etc.
>
> It's all abstracted so the core code doesn't know or care whether it's
> using a b-tree, GiST, or something completely different. Relevant lines:
>
> $ git grep '\<btinsert\>'
>
> backend/access/nbtree/nbtree.c:btinsert(PG_FUNCTION_ARGS)
>
> include/catalog/pg_am.h:DATA(insert OID = 403 ( btree 5 2 t f
> t t t t t t f t t 0 btinsert btbeginscan btgettuple btgetbitmap btrescan
> btendscan btmarkpos btrestrpos btbuild btbuildempty btbulkdelete
> btvacuumcleanup btcanreturn btcostestimate btoptions ));
>
> include/catalog/pg_proc.h:DATA(insert OID = 331 ( btinsert
> PGNSP PGUID 12 1 0 0 0 f f f f t f v 6 0 16 "2281 2281 2281 2281 2281
> 2281" _null_ _null_ _null_ _null_ btinsert _null_ _null_ _null_ ));
>
>
> See http://www.postgresql.org/docs/current/static/catalog-pg-am.html
>
> In psql:
>
> regress=> \x
> regress=> select * from pg_am where amname = 'btree';
> -[ RECORD 1 ]---+----------------
> amname | btree
> ... snip ...
> aminsert | btinsert
> ambeginscan | btbeginscan
> ... snip ...
>
>
> pg_catalog.pg_index rows refer to a vector of pg_opclass rows, one per
> index column, and that in turns refers to pg_am via the opcmethod column.
>
> http://www.postgresql.org/docs/current/static/catalog-pg-index.html
> http://www.postgresql.org/docs/current/static/catalog-pg-am.html
> http://www.postgresql.org/docs/current/static/catalog-pg-opclass.html
>
>
>
> See:
>
> This query demonstrates the relationship. It'd be smarter to properly
> separate out each column but I couldn't be bothered, so it just prints
> one row per index column in multicolumn indexes, not preserving order.
>
>
> regress=> select c.relname, oc.opcname, am.amname, am.aminsert
> from pg_index i
> inner join pg_class c on (i.indexrelid = c.oid)
> inner join pg_opclass oc ON (oc.oid = ANY(i.indclass))
> inner join pg_am am ON (oc.opcmethod = am.oid);
>
>
> All the executor knows is how to ask, eg "for this column of this index,
> what opclass was specified, and for that opclass, what is the oid of the
> function to perform the insert access-method operation".
>
> It has no idea it's calling btinsert.
>
> Try creating a GiST or GIN index and compare. It might help clarify things.
>
> > I want to understand the code flow for b tree index
>
> It'll take time, but stepping/jumping through it with a debugger will
> probably be a good way to do that. Connect a psql session, run "SELECT
> pg_backend_pid()", attach gdb to that pid, set breakpoints at the entry
> points of interest, cont, then run a command in psql that'll trigger one
> of the breakpoints. From there you can step through and watch what it
> does, using "next" to skip over function invocations you aren't
> interested in and "step" to enter ones you are.
>
> --
> Craig Ringer http://www.2ndQuadrant.com/
> PostgreSQL Development, 24x7 Support, Training & Services
>

Please tel me how to attached gdb to pid and debug.

Also what I understood from your reply is that everything is abstracted, so
am doesnot care abt backend implementation. Now, I want to modify B tree
indexing scheme. So, which files I should focus ?

Regards,
Rohit Goyal