On 07/26/2017 12:58 AM, David Raymond wrote:
Would you elaborate a bit more on that? To my untrained-in-C eyes it looks like
there's the outer transaction, then a savepoint1, then a loop of (savepoint2,
update the only record, release savepoint2). Is savepoint2 there not actually
getting released each time? Wouldn't the outer transaction and savepoint1 each
only need to hold the original 2 pages? Which of those is/are eating the
memory? Is it an SQL problem or a C problem that's causing it? And what's the
correct way?
It's an implementation artifact really.
Each time a page is modified within a savepoint, if the page has not
already been journalled within the current savepoint, a copy of it is
appended to the statement journal. In case you do "ROLLBACK TO" to
revert the change. But pages are never removed from the statement
journal - except that if the number of open savepoint transactions drops
to zero, the statement journal is truncated to zero bytes in size.
So opening and closing lots of nested savepoints while writing to the
database without ever closing the outermost savepoint can leave you with
a statement journal many times the size of the original database. With
the current implementation, the only way to avoid this is to ensure the
outermost savepoint is closed from time to time.
Dan.
-----Original Message-----
From: sqlite-users [mailto:sqlite-users-boun...@mailinglists.sqlite.org] On
Behalf Of Richard Hipp
Sent: Tuesday, July 25, 2017 1:35 PM
To: SQLite mailing list
Subject: Re: [sqlite] High memory usage for in-memory db with nested
transactions
Because of the way you have structured your SAVEPOINTs, the statement
log (used to ROLLBACK TO a prior savepoint) must add at least one new
page for each of your 500K UPDATEs. When the database file is on
disk, the statement log is a temporary file on disk which you are not
noticing. But when the database file is ":memory:" the statement log
is also in memory. 500K transactions at 4KB per page accounts for
most of the 2GB of memory used.
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