Hello John,
1) Quote from the same article:
Values are inserted into data page from the end to beginning. Items
are filled from beginning to end.
To address particular Key-Value pair ignite uses Link = Page ID +
order in page.
Link allows to read K,V pair as N-th item in page.
Simply put, external link to K,V pair consists of Page ID and number of
item in page.
Exact offset in page is not exposed to external link keeper (e.g. SQL
index) and saved inside page in corresponding "item". This is handy:
exact offset may change (for example, when we decide to defragment the
page) while item number always remains intact.
2) Item itself doesn't contain information about entry size. Every
payload piece keep its size in header. K,V pair may be stored either in
one payload piece (then its size is equal to size of payload piece) or
in several pieces on different pages (case when entry is too big for one
page).
Best Regards,
Ivan Rakov
On 20.06.2018 2:45, John Wilson wrote:
Hi,
1. An index page contains the hash value of key and a link; where a link
is page_id + offset. Question: what is this offset? Is it the offset to the
item in the data page? In other words, Ignite locates the page and the item
within the page and finally gets the key-value pair by following the item?
2. The design doc below states that the item serves as an internal
reference (offset) to the key value pair. Does the item has information
about the size of the key-value is it pointing to? If not, how does it now
the size of the key-value.
https://cwiki.apache.org/confluence/display/IGNITE/Ignite+Durable+Memory+-+under+the+hood
Thanks,
John
