https://bugs.openldap.org/show_bug.cgi?id=10072
Issue ID: 10072
Summary: Querying for transaction memory use
Product: LMDB
Version: unspecified
Hardware: All
OS: All
Status: UNCONFIRMED
Keywords: needs_review
Severity: normal
Priority: ---
Component: liblmdb
Assignee: [email protected]
Reporter: [email protected]
Target Milestone: ---
It would be useful to have a way to ask liblmdb how much "dirty memory" a
transaction is using, up to that point.
The goal is to be able to bundle writes into fewer transactions, making best
use of available memory and reducing total disc writes.
It is possible for an application to count the number of writes but this has
only a loose relation to the *actual* number of dirty pages flagged. The target
would be to write data up until the dirty memory gets to a threshold and then
commit.
I see that there's a:
txn->mt_dirty_room
and wonder if
MDB_IDL_UM_MAX - txn->mt_dirty_room
would give a count of that an "aware" application could make use of (an exact
count? or maybe a usable and sufficient indication?)
The need for this has been sharpened with the use of systemd service files that
cap the memory allowed for a process, for example:
MemoryHigh=512M
If the process reaches this limit and continues to write data, the system uses
swap.
See:
https://invent.kde.org/frameworks/baloo/-/merge_requests/148
Thank you for providing and supporting LMDB
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