Hi, On 2023-03-21 09:34:14 -0700, Andres Freund wrote: > On 2023-03-21 11:33:59 -0400, Robert Haas wrote: > > That feels like it would be slightly more rational behavior, > > but I'm not smart enough to guess whether anyone would actually be > > happier (or less happy) after such a change than they are now. > > Yea, I'm not either. The current behaviour does have the feature that it will > read in some data for each table, but limits trashing of shared buffers for > huge tables. That's good if your small to medium sized source database isn't > in s_b, because the next CREATE DATABASE has a change to not need to read the > data again. But if you have a source database with lots of small relations, it > can easily lead to swamping s_b.
Patch with the two minimal fixes attached. As we don't know whether it's worth changing the strategy, the more minimal fixes seem more appropriate. Greetings, Andres Freund
>From caa172f4faeb4a1c2f8c03d9c31f15d91c97dde3 Mon Sep 17 00:00:00 2001 From: Andres Freund <and...@anarazel.de> Date: Mon, 20 Mar 2023 21:57:40 -0700 Subject: [PATCH v1] Fix memory leak and inefficiency in CREATE DATABASE ... STRATEGY WAL_LOG RelationCopyStorageUsingBuffer() did not free the strategies used to access the source / target relation. They memory was released at the end of the transaction, but when using a template database with a lot of relations, the temporary leak can become big prohibitively big. RelationCopyStorageUsingBuffer() acquired the buffer for the target relation with RBM_NORMAL, therefore requiring a read of a block guaranteed to be zero. Use RBM_ZERO_AND_LOCK instead. Discussion: https://postgr.es/m/20230321070113.o2vqqxogjykwg...@awork3.anarazel.de --- src/backend/storage/buffer/bufmgr.c | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-) diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index 0a05577b68d..95212a39416 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -3833,11 +3833,9 @@ RelationCopyStorageUsingBuffer(RelFileLocator srclocator, LockBuffer(srcBuf, BUFFER_LOCK_SHARE); srcPage = BufferGetPage(srcBuf); - /* Use P_NEW to extend the destination relation. */ dstBuf = ReadBufferWithoutRelcache(dstlocator, forkNum, blkno, - RBM_NORMAL, bstrategy_dst, + RBM_ZERO_AND_LOCK, bstrategy_dst, permanent); - LockBuffer(dstBuf, BUFFER_LOCK_EXCLUSIVE); dstPage = BufferGetPage(dstBuf); START_CRIT_SECTION(); @@ -3855,6 +3853,9 @@ RelationCopyStorageUsingBuffer(RelFileLocator srclocator, UnlockReleaseBuffer(dstBuf); UnlockReleaseBuffer(srcBuf); } + + FreeAccessStrategy(bstrategy_src); + FreeAccessStrategy(bstrategy_dst); } /* --------------------------------------------------------------------- -- 2.38.0
