diff options
Diffstat (limited to 'src/backend/utils')
| -rw-r--r-- | src/backend/utils/sort/tuplestore.c | 73 |
1 files changed, 71 insertions, 2 deletions
diff --git a/src/backend/utils/sort/tuplestore.c b/src/backend/utils/sort/tuplestore.c index bcba30e5981..a5a56be91b2 100644 --- a/src/backend/utils/sort/tuplestore.c +++ b/src/backend/utils/sort/tuplestore.c @@ -57,6 +57,7 @@ #include "access/htup_details.h" #include "commands/tablespace.h" #include "executor/executor.h" +#include "miscadmin.h" #include "storage/buffile.h" #include "utils/memutils.h" #include "utils/resowner.h" @@ -1065,8 +1066,7 @@ tuplestore_gettupleslot(Tuplestorestate *state, bool forward, * tuplestore_advance - exported function to adjust position without fetching * * We could optimize this case to avoid palloc/pfree overhead, but for the - * moment it doesn't seem worthwhile. (XXX this probably needs to be - * reconsidered given the needs of window functions.) + * moment it doesn't seem worthwhile. */ bool tuplestore_advance(Tuplestorestate *state, bool forward) @@ -1089,6 +1089,75 @@ tuplestore_advance(Tuplestorestate *state, bool forward) } /* + * Advance over N tuples in either forward or back direction, + * without returning any data. N<=0 is a no-op. + * Returns TRUE if successful, FALSE if ran out of tuples. + */ +bool +tuplestore_skiptuples(Tuplestorestate *state, int64 ntuples, bool forward) +{ + TSReadPointer *readptr = &state->readptrs[state->activeptr]; + + Assert(forward || (readptr->eflags & EXEC_FLAG_BACKWARD)); + + if (ntuples <= 0) + return true; + + switch (state->status) + { + case TSS_INMEM: + if (forward) + { + if (readptr->eof_reached) + return false; + if (state->memtupcount - readptr->current >= ntuples) + { + readptr->current += ntuples; + return true; + } + readptr->current = state->memtupcount; + readptr->eof_reached = true; + return false; + } + else + { + if (readptr->eof_reached) + { + readptr->current = state->memtupcount; + readptr->eof_reached = false; + ntuples--; + } + if (readptr->current - state->memtupdeleted > ntuples) + { + readptr->current -= ntuples; + return true; + } + Assert(!state->truncated); + readptr->current = state->memtupdeleted; + return false; + } + break; + + default: + /* We don't currently try hard to optimize other cases */ + while (ntuples-- > 0) + { + void *tuple; + bool should_free; + + tuple = tuplestore_gettuple(state, forward, &should_free); + + if (tuple == NULL) + return false; + if (should_free) + pfree(tuple); + CHECK_FOR_INTERRUPTS(); + } + return true; + } +} + +/* * dumptuples - remove tuples from memory and write to tape * * As a side effect, we must convert each read pointer's position from |