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fix datapage padding behavior; the old padding overhead was ~ 100%; now it is much lower

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git-svn-id: svn+ssh://svn.corp.yahoo.com/yahoo/yrl/labs/pnuts/code/logstore@1522 8dad8b1f-cf64-0410-95b6-bcf113ffbcfe
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sears 2010-12-17 21:16:43 +00:00
parent 83fe4b7703
commit 42b52a4d17
1 changed files with 35 additions and 1 deletions
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36
datapage.cpp
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@ -270,8 +270,42 @@ bool DataPage<TUPLE>::read_data(byte * buf, off_t offset, size_t len) {
template <class TUPLE>
bool DataPage<TUPLE>::append(TUPLE const * dat)
{
// Don't append record to already-full datapage. The record could push us over the page limit, but that's OK.
// First, decide if we should append to this datapage, based on whether appending will waste more or less space than starting a new datapage
bool accept_tuple;
len_t tup_len = dat->byte_length();
// Decsion tree
if(write_offset_ > (initial_page_count_ * PAGE_SIZE)) {
// we already exceeded the page budget
if(write_offset_ > (2 * initial_page_count_ * PAGE_SIZE)) {
// ... by a lot. Reject regardless.
accept_tuple = false;
} else {
// ... by a little bit. Accept tuple if it fits on this page.
accept_tuple = (((write_offset_-1) & ~(PAGE_SIZE-1)) == (((write_offset_ + tup_len)-1) & ~(PAGE_SIZE-1)));
}
} else {
if(write_offset_ + tup_len < (initial_page_count_ * PAGE_SIZE)) {
// tuple fits. contractually obligated to accept it.
accept_tuple = true;
} else if(write_offset_ == 0) {
// datapage is emptry. contractually obligated to accept tuple.
accept_tuple = true;
} else {
if(tup_len > initial_page_count_ * PAGE_SIZE) {
// this is a "big tuple"
len_t reject_padding = PAGE_SIZE - (write_offset_ & PAGE_SIZE-1);
len_t accept_padding = PAGE_SIZE - ((write_offset_ + tup_len) & PAGE_SIZE-1);
accept_tuple = accept_padding < reject_padding;
} else {
// this is a "small tuple"; only exceed budget if doing so leads to < 33% overhead for this data.
len_t accept_padding = PAGE_SIZE - (write_offset_ & PAGE_SIZE-1);
accept_tuple = (3*accept_padding) < tup_len;
}
}
}
if(!accept_tuple) {
DEBUG("offset %lld closing datapage\n", write_offset_);
return false;
}