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Add lo_truncate() to backend and libpq for large object truncation.
Kris Jurka
This commit is contained in:
Bruce Momjian
@@ -17,7 +17,7 @@
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*
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*
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* IDENTIFICATION
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* $PostgreSQL: pgsql/src/backend/storage/large_object/inv_api.c,v 1.122 2007/02/27 23:48:07 tgl Exp $
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* $PostgreSQL: pgsql/src/backend/storage/large_object/inv_api.c,v 1.123 2007/03/03 19:52:46 momjian Exp $
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*
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*-------------------------------------------------------------------------
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*/
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@@ -681,3 +681,166 @@ inv_write(LargeObjectDesc *obj_desc, const char *buf, int nbytes)
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return nwritten;
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}
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void
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inv_truncate(LargeObjectDesc *obj_desc, int len)
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{
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int32 pageno = (int32) (len / LOBLKSIZE);
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int off;
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ScanKeyData skey[2];
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IndexScanDesc sd;
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HeapTuple oldtuple;
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Form_pg_largeobject olddata;
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struct
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{
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bytea hdr;
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char data[LOBLKSIZE];
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} workbuf;
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char *workb = VARDATA(&workbuf.hdr);
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HeapTuple newtup;
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Datum values[Natts_pg_largeobject];
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char nulls[Natts_pg_largeobject];
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char replace[Natts_pg_largeobject];
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CatalogIndexState indstate;
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Assert(PointerIsValid(obj_desc));
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/* enforce writability because snapshot is probably wrong otherwise */
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if ((obj_desc->flags & IFS_WRLOCK) == 0)
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ereport(ERROR,
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(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
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errmsg("large object %u was not opened for writing",
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obj_desc->id)));
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open_lo_relation();
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indstate = CatalogOpenIndexes(lo_heap_r);
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ScanKeyInit(&skey[0],
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Anum_pg_largeobject_loid,
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BTEqualStrategyNumber, F_OIDEQ,
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ObjectIdGetDatum(obj_desc->id));
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ScanKeyInit(&skey[1],
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Anum_pg_largeobject_pageno,
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BTGreaterEqualStrategyNumber, F_INT4GE,
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Int32GetDatum(pageno));
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sd = index_beginscan(lo_heap_r, lo_index_r,
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obj_desc->snapshot, 2, skey);
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/*
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* If possible, get the page the truncation point is in.
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* The truncation point may be beyond the end of the LO or
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* in a hole.
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*/
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olddata = NULL;
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if ((oldtuple = index_getnext(sd, ForwardScanDirection)) != NULL)
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{
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olddata = (Form_pg_largeobject) GETSTRUCT(oldtuple);
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Assert(olddata->pageno >= pageno);
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}
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/*
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* If we found the page of the truncation point we need to
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* truncate the data in it. Otherwise if we're in a hole,
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* we need to create a page to mark the end of data.
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*/
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if (olddata != NULL && olddata->pageno == pageno)
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{
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/* First, load old data into workbuf */
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bytea *datafield = &(olddata->data);
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bool pfreeit = false;
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int pagelen;
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if (VARATT_IS_EXTENDED(datafield))
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{
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datafield = (bytea *)
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heap_tuple_untoast_attr((varattrib *) datafield);
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pfreeit = true;
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}
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pagelen = getbytealen(datafield);
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Assert(pagelen <= LOBLKSIZE);
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memcpy(workb, VARDATA(datafield), pagelen);
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if (pfreeit)
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pfree(datafield);
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/*
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* Fill any hole
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*/
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off = len % LOBLKSIZE;
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if (off > pagelen)
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MemSet(workb + pagelen, 0, off - pagelen);
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/* compute length of new page */
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SET_VARSIZE(&workbuf.hdr, off + VARHDRSZ);
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/*
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* Form and insert updated tuple
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*/
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memset(values, 0, sizeof(values));
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memset(nulls, ' ', sizeof(nulls));
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memset(replace, ' ', sizeof(replace));
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values[Anum_pg_largeobject_data - 1] = PointerGetDatum(&workbuf);
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replace[Anum_pg_largeobject_data - 1] = 'r';
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newtup = heap_modifytuple(oldtuple, RelationGetDescr(lo_heap_r),
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values, nulls, replace);
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simple_heap_update(lo_heap_r, &newtup->t_self, newtup);
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CatalogIndexInsert(indstate, newtup);
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heap_freetuple(newtup);
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}
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else
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{
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/*
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* If the first page we found was after the truncation
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* point, we're in a hole that we'll fill, but we need to
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* delete the later page.
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*/
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if (olddata != NULL && olddata->pageno > pageno)
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simple_heap_delete(lo_heap_r, &oldtuple->t_self);
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/*
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* Write a brand new page.
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*
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* Fill the hole up to the truncation point
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*/
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off = len % LOBLKSIZE;
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if (off > 0)
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MemSet(workb, 0, off);
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/* compute length of new page */
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SET_VARSIZE(&workbuf.hdr, off + VARHDRSZ);
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/*
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* Form and insert new tuple
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*/
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memset(values, 0, sizeof(values));
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memset(nulls, ' ', sizeof(nulls));
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values[Anum_pg_largeobject_loid - 1] = ObjectIdGetDatum(obj_desc->id);
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values[Anum_pg_largeobject_pageno - 1] = Int32GetDatum(pageno);
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values[Anum_pg_largeobject_data - 1] = PointerGetDatum(&workbuf);
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newtup = heap_formtuple(lo_heap_r->rd_att, values, nulls);
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simple_heap_insert(lo_heap_r, newtup);
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CatalogIndexInsert(indstate, newtup);
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heap_freetuple(newtup);
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}
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/*
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* Delete any pages after the truncation point
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*/
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while ((oldtuple = index_getnext(sd, ForwardScanDirection)) != NULL)
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{
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simple_heap_delete(lo_heap_r, &oldtuple->t_self);
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}
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index_endscan(sd);
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CatalogCloseIndexes(indstate);
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/*
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* Advance command counter so that tuple updates will be seen by later
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* large-object operations in this transaction.
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*/
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CommandCounterIncrement();
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}
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