On Tue, Nov 19, 2013 at 11:52 AM, Craig Ringer <cr...@2ndquadrant.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
