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[Issue 9434] New: Abysmal write performance with certain data patterns
by openldap-its＠openldap.org 15 Apr '26

15 Apr '26

https://bugs.openldap.org/show_bug.cgi?id=9434 Issue ID: 9434 Summary: Abysmal write performance with certain data patterns Product: LMDB Version: 0.9.24 Hardware: x86_64 OS: Linux Status: UNCONFIRMED Severity: normal Priority: --- Component: liblmdb Assignee: bugs(a)openldap.org Reporter: tina(a)tina.pm Target Milestone: --- Created attachment 784 --> https://bugs.openldap.org/attachment.cgi?id=784&action=edit Monitoring graph of disk usage Hi, I have recently written a project for a customer which relies heavily on LMDB, in which performance is critical. Sadly, after completing the project I started having all kinds of problems when the DB started to grow. This has gotten so bad the project release had to be postponed, and I have been asked to rewrite the DB layer using a different engine, unless I can find some solution quickly. I have so far found 4 serious issues, which I suspect are related either to the size of the database or to the patterns of the data: * Writing a value in some of the subdatabases has become increasingly slower, and commits are taking way too long to complete. This is running on a powerful computer with SSDs, and the 95% percentile of commits is at around 400ms. The single-writer limitation meant that I have run out of optimisations to try. * For some reason I cannot understand, the disk usage has grown to over 2x the size of the actual data stored, and the free space does not seem to be reclaimed. The file takes up 348 GB, while the used pages amount to only 162 GB. * A couple of days ago it had a sudden spike in disk usage (not correlated to increases in actual data stored, or even to the last pageno user) that filled the disk in a couple of hours. You can see this in the attached captures of the monitoring graphs which show actual disk usage (bottom) and counts of pages as reported by LMDB (top). The bottom graph is total disk usage, although the partition is almost exclusively the database, but ignore the few dips in size which are from removing other stuff. * Running `mdb_dump` for backups takes up to 7 hours for the database; restores are totally useless: I tried to re-create the database after the weird space spike and had to stopped after 24h when not even 30% of the data ad been restored! This alone is a deal-breaker, as we have no usable way to backup and restore the database. For context, this is the mdb_stat output with descriptions of each subdatabase. I have no explanation for the ridiculous amount of free pages, and even running mdb_stat takes a few seconds: Environment Info Map address: (nil) Map size: 397166026752 Page size: 4096 Max pages: 96964362 Number of pages used: 90991042 Last transaction ID: 14647267 Max readers: 126 Number of readers used: 4 Freelist Status Tree depth: 3 Branch pages: 26 Leaf pages: 5168 Overflow pages: 74319 Entries: 111981 Free pages: 36352392 Status of Main DB Tree depth: 1 Branch pages: 0 Leaf pages: 1 Overflow pages: 0 Entries: 8 Status of audit_log Tree depth: 4 Branch pages: 309 Leaf pages: 69154 Overflow pages: 6082343 Entries: 2061655 * Audit log: MDB_INTEGERKEY, big values (12kb av). Append only, few reads. Status of audit_idx Tree depth: 4 Branch pages: 261 Leaf pages: 27310 Overflow pages: 0 Entries: 2006963 * Audit index 1: 40 byte keys, 8 byte values. Append only, it has less records as I disabled it yesterday due to its impact on performance. Status of time_idx Tree depth: 3 Branch pages: 22 Leaf pages: 4611 Overflow pages: 0 Entries: 2061655 * Audit index 2: MDB_INTEGERKEY, MDB_DUPSORT, MDB_DUPFIXED; 40 byte values. Append only. Status of item_db Tree depth: 4 Branch pages: 132 Leaf pages: 10040 Overflow pages: 0 Entries: 186291 * Main data store: 40 byte keys, small values (220b avg). Lots of reads and new records, very few deletes and no updates. Status of user_state_db Tree depth: 5 Branch pages: 83283 Leaf pages: 9289578 Overflow pages: 32 Entries: 207894432 * User state: 20-40 byte keys, small values (180b avg), *many* entries. Lots and reads and updates. Status of item_users_idx Tree depth: 4 Branch pages: 203 Leaf pages: 16532 Overflow pages: 0 Entries: 1035586217 * User / data matrix index: MDB_DUPSORT; 40 byte keys, 20-40 byte values, *really big*. Lots of writes, very few deletes and no updates. Status of user_log Tree depth: 5 Branch pages: 361275 Leaf pages: 26570347 Overflow pages: 0 Entries: 1035586217 * User log: 30-50 byte keys, small values (100b avg), 1e9 records. Append only, very few reads. I had to stop the restore operation while this was being recreated, because after 24h only 50% the entries had been restored. Thanks to monitoring, I measured this maxing out at 7000 entries per second; the other databases showed way slower rates than this! Any help would be really appreciated! Thanks. Tina. -- You are receiving this mail because: You are on the CC list for the issue.

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[Issue 9316] New: performance issue when writing a high number of large objects
by openldap-its＠openldap.org 15 Apr '26

15 Apr '26

https://bugs.openldap.org/show_bug.cgi?id=9316 Issue ID: 9316 Summary: performance issue when writing a high number of large objects Product: LMDB Version: 0.9.24 Hardware: x86_64 OS: Linux Status: UNCONFIRMED Severity: normal Priority: --- Component: liblmdb Assignee: bugs(a)openldap.org Reporter: JGabler(a)univa.com Target Milestone: --- Created attachment 755 --> https://bugs.openldap.org/attachment.cgi?id=755&action=edit lmdb performance test reproducing the issue When writing a high number of big objects we see an extreme variation in performance from very fast to extremely slow. In the test scenario we write 10 chunks of 10.000 "jobs" (some 10kB) and their corresponding "job script" (some 40kB), 200.000 objects in total. Then delete all objects. We do 10 iterations of this scenario. When running this scenario as part of Univa Grid Engine with LMDB as database backend we get the following performance values (rows are the iteration, columns the chunk of jobs): Iteration 0 1 2 3 4 5 6 7 8 9 0 21.525 21.250 21.574 21.722 22.693 21.992 22.438 22.650 21.972 22.017 1 22.262 21.656 22.339 22.914 21.549 24.906 23.862 1531.189 1695.041 1491.255 2 36.071 21.619 22.074 22.927 23.455 27.239 22.640 22.802 633.956 1882.008 3 52.163 21.651 21.571 22.686 22.727 22.024 40.980 22.156 22.429 595.362 4 64.977 21.511 22.519 22.148 22.354 23.292 57.740 20.835 37.680 250.594 5 54.724 21.074 21.200 23.744 22.109 21.351 62.225 21.447 91.292 375.260 6 49.065 21.573 22.309 26.084 21.226 21.248 68.580 22.531 59.338 249.936 7 44.666 21.830 21.009 28.760 21.533 21.611 72.291 23.144 86.281 118.326 8 35.486 21.720 21.840 24.729 22.045 20.877 76.473 21.193 120.387 136.836 9 41.159 23.365 21.721 23.024 21.835 20.972 77.409 21.784 193.885 306.158 So usually writing of 10.000 "jobs"+"job_script" takes some 22 seconds but after some time performance massively breaks in. With other database backends we do not see this behaviour, see the following performance data of the same test done with PostgreSQL backend which is slower (as expected going over the network) but provides constant throughput: Iteration 0 1 2 3 4 5 6 7 8 9 0 36.937 37.110 36.952 37.279 37.580 37.364 37.950 37.390 37.682 37.439 1 37.464 38.110 37.679 38.366 37.576 37.624 37.476 37.412 37.265 37.727 2 36.394 37.635 37.347 37.603 37.402 37.515 37.802 37.898 37.355 37.939 3 37.213 37.539 36.771 37.706 37.055 37.780 37.283 37.488 36.955 37.460 4 36.554 37.557 37.368 37.960 37.070 37.892 37.459 37.857 37.228 37.833 5 37.047 38.164 37.167 37.885 37.268 37.676 37.355 37.572 37.347 37.569 6 37.118 37.735 36.857 37.602 36.717 37.716 37.444 37.685 37.085 38.151 7 36.787 37.647 36.844 37.601 36.934 37.440 37.632 37.291 37.174 37.926 8 36.884 37.560 37.117 37.239 37.034 37.748 37.289 37.635 36.822 37.693 9 37.178 37.496 36.849 37.799 37.289 37.644 37.461 37.622 37.022 37.670 We can reproduce the issue with a small C program (see attachment) which does essentially the same database operations as our database layer in Univa Grid Engine but depends only on liblmdb. It simulates the scenario described above and gives us the following performance data showing the extreme performance variation: Iteration 0 1 2 3 4 5 6 7 8 9 0 0.686 0.625 0.660 0.637 0.631 0.741 0.757 0.658 0.651 0.614 1 0.705 0.838 0.690 0.772 0.663 3.248 0.605 542.762 1114.374 898.477 2 13.336 1.299 0.659 0.637 0.626 0.712 11.172 0.663 29.833 1161.884 3 26.774 0.647 0.607 0.586 0.583 0.639 24.893 0.629 3.837 423.248 4 32.802 0.629 0.616 0.560 0.550 0.605 31.133 0.625 6.606 195.150 5 34.819 0.623 0.628 0.582 0.564 0.609 32.275 0.607 7.599 134.106 6 26.319 0.622 0.582 0.548 0.551 0.590 28.536 0.611 36.429 160.781 7 21.878 0.814 0.668 0.736 0.614 0.543 24.355 0.626 36.583 148.337 8 4.129 0.654 5.674 0.596 0.566 0.554 7.158 0.633 0.599 48.799 9 30.278 0.608 0.608 0.560 0.549 0.587 29.253 0.606 9.593 128.339 It can be compiled on Linux 64bit with gcc -I <path to lmdb>/include -L <path to lmdb>/lib -o test_lmdb_perf test_lmdb_perf.c -llmdb To run the given scenario call it with the following parameters: ./test_lmdb_perf <path to database directory> 10 10 10000 We built and ran it on - CentOS Linux release 7.7.1908 (Core) - Linux biber 3.10.0-1062.9.1.el7.x86_64 #1 SMP Fri Dec 6 15:49:49 UTC 2019 x86_64 x86_64 x86_64 GNU/Linux - it was built with gcc (GCC) 7.2.1 20170829 (Red Hat 7.2.1-1) from devtoolset-7 -- You are receiving this mail because: You are on the CC list for the issue.

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[Issue 9278] New: liblmdb: robust mutexes should not be unmapped
by openldap-its＠openldap.org 15 Apr '26

15 Apr '26

https://bugs.openldap.org/show_bug.cgi?id=9278 Issue ID: 9278 Summary: liblmdb: robust mutexes should not be unmapped Product: LMDB Version: unspecified Hardware: All OS: FreeBSD Status: UNCONFIRMED Severity: normal Priority: --- Component: liblmdb Assignee: bugs(a)openldap.org Reporter: delphij(a)freebsd.org Target Milestone: --- Created attachment 736 --> https://bugs.openldap.org/attachment.cgi?id=736&action=edit A possible workaround We recently noticed that lmdb would have the memory region containing the robust mutex unmapped on mdb_env_close0(): munmap((void *)env->me_txns, (env->me_maxreaders-1)*sizeof(MDB_reader)+sizeof(MDB_txninfo)); Note that if this is the last unmap for a robust mutex, the FreeBSD implementation would garbage-collect the mutex, making it no longer visible to other processes. As the result, a second instance of the attached test.c (from https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=244493 with minor changes) would trigger the assertion at mdb_txn_begin() because the acquisition of the mutex would return 22 (EINVAL), because the mutex appeared to be a robust mutex, but was invalid. The attached lmdb.diff is a possible workaround for this (it would skip unmapping when setting up the robust mutex for the first time). -- You are receiving this mail because: You are on the CC list for the issue.

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[Issue 8986] [PATCH] Fix union semun undefined from FreeBSD 12 onward
by openldap-its＠openldap.org 15 Apr '26

15 Apr '26

https://bugs.openldap.org/show_bug.cgi?id=8986 Howard Chu <hyc(a)openldap.org> changed: What |Removed |Added ---------------------------------------------------------------------------- Status|UNCONFIRMED |RESOLVED Resolution|--- |DUPLICATE --- Comment #7 from Howard Chu <hyc(a)openldap.org> --- Obsoleted by ITS#9278, FreeBSD 11 supports robust POSIX mutexes so we don't need semaphore support. *** This issue has been marked as a duplicate of issue 9278 *** -- You are receiving this mail because: You are on the CC list for the issue.

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[Issue 8824] openldap-2.4.46/libraries/liblmdb/mdb_dump.c:136]: (style) Suspicious condition
by openldap-its＠openldap.org 15 Apr '26

15 Apr '26

https://bugs.openldap.org/show_bug.cgi?id=8824 Howard Chu <hyc(a)openldap.org> changed: What |Removed |Added ---------------------------------------------------------------------------- Resolution|--- |TEST Status|UNCONFIRMED |RESOLVED --- Comment #1 from Howard Chu <hyc(a)openldap.org> --- Thanks for the report, fixed in git -- You are receiving this mail because: You are on the CC list for the issue.

1 0

[Issue 8784] SIGBUS in mdb_page_touch
by openldap-its＠openldap.org 15 Apr '26

15 Apr '26

https://bugs.openldap.org/show_bug.cgi?id=8784 Howard Chu <hyc(a)openldap.org> changed: What |Removed |Added ---------------------------------------------------------------------------- Resolution|--- |INVALID OS|All |Android Status|UNCONFIRMED |RESOLVED Hardware|All |Other --- Comment #4 from Howard Chu <hyc(a)openldap.org> --- Hasn't reappeared since Android 9, probably an Android bug and not an LMDB bug -- You are receiving this mail because: You are on the CC list for the issue.

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[Issue 8483] CMake buildsystem support for LMDB
by openldap-its＠openldap.org 15 Apr '26

15 Apr '26

https://bugs.openldap.org/show_bug.cgi?id=8483 Howard Chu <hyc(a)openldap.org> changed: What |Removed |Added ---------------------------------------------------------------------------- Status|UNCONFIRMED |RESOLVED Resolution|--- |WONTFIX --- Comment #6 from Howard Chu <hyc(a)openldap.org> --- We don't support multiple build systems. -- You are receiving this mail because: You are on the CC list for the issue.

1 0

[Issue 8913] Add meson build system to lmdb
by openldap-its＠openldap.org 15 Apr '26

15 Apr '26

https://bugs.openldap.org/show_bug.cgi?id=8913 Howard Chu <hyc(a)openldap.org> changed: What |Removed |Added ---------------------------------------------------------------------------- Status|UNCONFIRMED |RESOLVED Resolution|--- |DUPLICATE --- Comment #6 from Howard Chu <hyc(a)openldap.org> --- We won't support multiple build systems. *** This issue has been marked as a duplicate of issue 8483 *** -- You are receiving this mail because: You are on the CC list for the issue.

1 0

[Issue 8483] CMake buildsystem support for LMDB
by openldap-its＠openldap.org 15 Apr '26

15 Apr '26

https://bugs.openldap.org/show_bug.cgi?id=8483 Howard Chu <hyc(a)openldap.org> changed: What |Removed |Added ---------------------------------------------------------------------------- CC| |nacho.resa(a)gmail.com --- Comment #5 from Howard Chu <hyc(a)openldap.org> --- *** Issue 8913 has been marked as a duplicate of this issue. *** -- You are receiving this mail because: You are on the CC list for the issue.

1 0

[Issue 9528] New: liblmdb throws away environment CFLAGS
by openldap-its＠openldap.org 15 Apr '26

15 Apr '26

https://bugs.openldap.org/show_bug.cgi?id=9528 Issue ID: 9528 Summary: liblmdb throws away environment CFLAGS Product: LMDB Version: 0.9.29 Hardware: All OS: All Status: UNCONFIRMED Severity: normal Priority: --- Component: liblmdb Assignee: bugs(a)openldap.org Reporter: quanah(a)openldap.org Target Milestone: --- When building LMDB, specified hardening flags are thrown away due to the Makefile overriding CFLAGS: Makefile:CFLAGS = $(THREADS) $(OPT) $(W) $(XCFLAGS) -- You are receiving this mail because: You are on the CC list for the issue.

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