$PostgreSQL: pgsql/contrib/pgrowlocks/README.pgrowlocks,v 1.1 2006/04/23 01:12:58 ishii Exp $

$PostgreSQL: pgsql/contrib/pgrowlocks/README.pgrowlocks,v 1.2 2007/08/27 00:13:51 tgl Exp $

pgrowlocks READMETatsuo Ishii

1. What is pgrowlocks?

pgrowlocks shows row locking information for specified table.

pgrowlocks returns followingdata type:

pgrowlocks returns followingcolumns:

CREATE TYPE pgrowlocks_type AS (

locked_row TID,-- row TID

lock_type TEXT,-- lock type

locker XID,-- locking XID

multi bool,-- multi XID?

xids xid[],-- multi XIDs

pids INTEGER[]-- locker's process id

);

Here is a sample execution of pgrowlocks:

3. How to use pgrowlocks

The calling sequence for pgrowlocks is as follows:

CREATE OR REPLACE FUNCTION pgrowlocks(text) RETURNS pgrowlocks_type

AS 'MODULE_PATHNAME', 'pgrowlocks'

LANGUAGE 'c' WITH (isstrict);

The parameter is a name of table. pgrowlocks returns type pgrowlocks_type.

pgrowlocks grab AccessShareLock for the target table and read each

row one by one to get the row locking information. You should

notice that:

PG_MODULE_MAGIC;

#defineDUMMY_TUPLE "public.pgrowlocks_type"

#defineNCHARS 32

#undef MAKERANGEVARFROMNAMELIST_HAS_TWO_ARGS

{

Relationrel;

MyData*mydata;

Relationrel;

if (!superuser())

ereport(ERROR,

(errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),

(errmsg("must be superuser to use pgrowlocks"))));

if (SRF_IS_FIRSTCALL())

{

text*relname;

funcctx=SRF_FIRSTCALL_INIT();

oldcontext=MemoryContextSwitchTo(funcctx->multi_call_memory_ctx);

tupdesc=RelationNameGetTupleDesc(DUMMY_TUPLE);

if (get_call_result_type(fcinfo,NULL,&tupdesc)!=TYPEFUNC_COMPOSITE)

elog(ERROR,"return type must be a row type");

attinmeta=TupleDescGetAttInMetadata(tupdesc);

funcctx->attinmeta=attinmeta;

relname=PG_GETARG_TEXT_P(0);

relrv=makeRangeVarFromNameList(textToQualifiedNameList(relname,"pgrowlocks"));

relrv=makeRangeVarFromNameList(textToQualifiedNameList(relname));

rel=heap_openrv(relrv,AccessShareLock);

scan=heap_beginscan(rel,SnapshotNow,0,NULL);

mydata=palloc(sizeof(*mydata));

mydata->rel=rel;

i=0;

values[i++]= (char*)DirectFunctionCall1(tidout,PointerGetDatum(&tuple->t_self));

if (tuple->t_data->t_infomask&HEAP_XMAX_SHARED_LOCK)

values[i++]=pstrdup("Shared");

values[i++]=pstrdup("Exclusive");

values[i++]=pstrdup("Exclusive");

values[i]=palloc(NCHARS*sizeof(char));

snprintf(values[i++],NCHARS,"%d",HeapTupleHeaderGetXmax(tuple->t_data));

if (tuple->t_data->t_infomask&HEAP_XMAX_IS_MULTI)

{

TransactionId*xids;

values[i]=palloc(NCHARS*sizeof(char));

snprintf(values[i++],NCHARS,"{%d}",BackendXidGetPid(HeapTupleHeaderGetXmax(tuple->t_data)));

}

values[i++]=pstrdup("false");

values[i++]=pstrdup("{}");

values[i++]=pstrdup("{}");

LockBuffer(scan->rs_cbuf,BUFFER_LOCK_UNLOCK);

-- Adjust this setting to control where the objects get created.

SET search_path = public;

CREATE TYPE pgrowlocks_type AS (

locked_row TID,-- row TID

lock_type TEXT,-- lock type

locker XID,-- locking XID

multi bool,-- multi XID?

xids xid[],-- multi XIDs

pids INTEGER[]-- locker's process id

);

CREATE OR REPLACE FUNCTION pgrowlocks(text)

RETURNS setof pgrowlocks_type

CREATE OR REPLACE FUNCTION pgrowlocks(IN relname text,

OUT locked_row TID,-- row TID

OUT lock_type TEXT,-- lock type

OUT locker XID,-- locking XID

OUT multi bool,-- multi XID?

OUT xids xid[],-- multi XIDs

OUT pids INTEGER[])-- locker's process id

RETURNS SETOF record

AS 'MODULE_PATHNAME', 'pgrowlocks'

LANGUAGE'C' STRICT;

LANGUAGEC STRICT;

SET search_path= public;

DROPFUNCTION pgrowlocks(text);

DROPTYPE pgrowlocks_type;