mirror of https://github.com/postgres/postgres
Avoid unnecessary streaming of transactions during logical replication.
After restart, we don't perform streaming of an in-progress transaction if it was previously decoded and confirmed by the client. To achieve that we were comparing the END location of the WAL record being decoded with the WAL location we have already decoded and confirmed by the client. While decoding the commit record, to decide whether to process and send the complete transaction, we compare its START location with the WAL location we have already decoded and confirmed by the client. Now, if we need to queue some change in the transaction while decoding the commit record (e.g. snapshot), it is possible that we decide to stream the transaction but later commit processing decides to skip it. In such a case, we would needlessly send the changes and later when we decide to skip it, we will send stream abort. We also sometimes decide to stream the changes when we actually just need to process them locally like a change for invalidations. This will lead us to send empty streams. To avoid this, while queuing each change for decoding, we remember whether the transaction has any change that actually needs to be sent downstream and use that information later to decide whether to stream the transaction or not. Note, we can't avoid all cases where we have to send empty streams like the case where the plugin later decides that the change is not publishable. However, we will no longer need to send stream_abort when we skip sending a particular transaction. Author: Dilip Kumar Reviewed-by: Hou Zhijie, Ashutosh Bapat, Shi yu, Amit Kapila Discussion: https://postgr.es/m/CAFiTN-tHK=7LzfrPs8fbT2ksrOJGQbzywcgXst2bM9-rJJAAUg@mail.gmail.com
This commit is contained in:
Amit Kapila
parent
3f0e786ccb
commit
bf07ab492c
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@ -695,9 +695,9 @@ ReorderBufferTXNByXid(ReorderBuffer *rb, TransactionId xid, bool create,
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* Record the partial change for the streaming of in-progress transactions. We
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* can stream only complete changes so if we have a partial change like toast
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* table insert or speculative insert then we mark such a 'txn' so that it
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* can't be streamed. We also ensure that if the changes in such a 'txn' are
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* above logical_decoding_work_mem threshold then we stream them as soon as we
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* have a complete change.
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* can't be streamed. We also ensure that if the changes in such a 'txn' can
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* be streamed and are above logical_decoding_work_mem threshold then we stream
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* them as soon as we have a complete change.
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*/
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static void
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ReorderBufferProcessPartialChange(ReorderBuffer *rb, ReorderBufferTXN *txn,
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@ -762,7 +762,8 @@ ReorderBufferProcessPartialChange(ReorderBuffer *rb, ReorderBufferTXN *txn,
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*/
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if (ReorderBufferCanStartStreaming(rb) &&
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!(rbtxn_has_partial_change(toptxn)) &&
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rbtxn_is_serialized(txn))
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rbtxn_is_serialized(txn) &&
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rbtxn_has_streamable_change(toptxn))
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ReorderBufferStreamTXN(rb, toptxn);
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}
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@ -793,6 +794,29 @@ ReorderBufferQueueChange(ReorderBuffer *rb, TransactionId xid, XLogRecPtr lsn,
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return;
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}
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/*
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* The changes that are sent downstream are considered streamable. We
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* remember such transactions so that only those will later be considered
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* for streaming.
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*/
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if (change->action == REORDER_BUFFER_CHANGE_INSERT ||
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change->action == REORDER_BUFFER_CHANGE_UPDATE ||
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change->action == REORDER_BUFFER_CHANGE_DELETE ||
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change->action == REORDER_BUFFER_CHANGE_INTERNAL_SPEC_INSERT ||
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change->action == REORDER_BUFFER_CHANGE_TRUNCATE ||
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change->action == REORDER_BUFFER_CHANGE_MESSAGE)
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{
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ReorderBufferTXN *toptxn;
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/* get the top transaction */
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if (txn->toptxn != NULL)
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toptxn = txn->toptxn;
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else
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toptxn = txn;
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toptxn->txn_flags |= RBTXN_HAS_STREAMABLE_CHANGE;
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}
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change->lsn = lsn;
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change->txn = txn;
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@ -2942,9 +2966,8 @@ ReorderBufferForget(ReorderBuffer *rb, TransactionId xid, XLogRecPtr lsn)
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if (txn == NULL)
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return;
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/* For streamed transactions notify the remote node about the abort. */
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if (rbtxn_is_streamed(txn))
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rb->stream_abort(rb, txn, lsn);
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/* this transaction mustn't be streamed */
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Assert(!rbtxn_is_streamed(txn));
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/* cosmetic... */
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txn->final_lsn = lsn;
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@ -3460,14 +3483,15 @@ ReorderBufferLargestTXN(ReorderBuffer *rb)
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}
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/*
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* Find the largest toplevel transaction to evict (by streaming).
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* Find the largest streamable toplevel transaction to evict (by streaming).
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*
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* This can be seen as an optimized version of ReorderBufferLargestTXN, which
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* should give us the same transaction (because we don't update memory account
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* for subtransaction with streaming, so it's always 0). But we can simply
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* iterate over the limited number of toplevel transactions that have a base
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* snapshot. There is no use of selecting a transaction that doesn't have base
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* snapshot because we don't decode such transactions.
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* snapshot because we don't decode such transactions. Also, we do not select
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* the transaction which doesn't have any streamable change.
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*
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* Note that, we skip transactions that contains incomplete changes. There
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* is a scope of optimization here such that we can select the largest
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@ -3483,7 +3507,7 @@ ReorderBufferLargestTXN(ReorderBuffer *rb)
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* the subxact from where we streamed the last change.
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*/
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static ReorderBufferTXN *
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ReorderBufferLargestTopTXN(ReorderBuffer *rb)
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ReorderBufferLargestStreamableTopTXN(ReorderBuffer *rb)
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{
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dlist_iter iter;
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Size largest_size = 0;
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@ -3502,7 +3526,8 @@ ReorderBufferLargestTopTXN(ReorderBuffer *rb)
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Assert(txn->base_snapshot != NULL);
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if ((largest == NULL || txn->total_size > largest_size) &&
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(txn->total_size > 0) && !(rbtxn_has_partial_change(txn)))
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(txn->total_size > 0) && !(rbtxn_has_partial_change(txn)) &&
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rbtxn_has_streamable_change(txn))
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{
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largest = txn;
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largest_size = txn->total_size;
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@ -3547,7 +3572,7 @@ ReorderBufferCheckMemoryLimit(ReorderBuffer *rb)
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* memory by streaming, if possible. Otherwise, spill to disk.
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*/
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if (ReorderBufferCanStartStreaming(rb) &&
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(txn = ReorderBufferLargestTopTXN(rb)) != NULL)
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(txn = ReorderBufferLargestStreamableTopTXN(rb)) != NULL)
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{
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/* we know there has to be one, because the size is not zero */
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Assert(txn && !txn->toptxn);
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@ -3919,7 +3944,7 @@ ReorderBufferCanStartStreaming(ReorderBuffer *rb)
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* restarting.
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*/
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if (ReorderBufferCanStream(rb) &&
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!SnapBuildXactNeedsSkip(builder, ctx->reader->EndRecPtr))
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!SnapBuildXactNeedsSkip(builder, ctx->reader->ReadRecPtr))
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return true;
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return false;
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@ -168,14 +168,15 @@ typedef struct ReorderBufferChange
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} ReorderBufferChange;
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/* ReorderBufferTXN txn_flags */
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#define RBTXN_HAS_CATALOG_CHANGES 0x0001
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#define RBTXN_IS_SUBXACT 0x0002
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#define RBTXN_IS_SERIALIZED 0x0004
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#define RBTXN_IS_SERIALIZED_CLEAR 0x0008
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#define RBTXN_IS_STREAMED 0x0010
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#define RBTXN_HAS_PARTIAL_CHANGE 0x0020
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#define RBTXN_PREPARE 0x0040
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#define RBTXN_SKIPPED_PREPARE 0x0080
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#define RBTXN_HAS_CATALOG_CHANGES 0x0001
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#define RBTXN_IS_SUBXACT 0x0002
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#define RBTXN_IS_SERIALIZED 0x0004
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#define RBTXN_IS_SERIALIZED_CLEAR 0x0008
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#define RBTXN_IS_STREAMED 0x0010
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#define RBTXN_HAS_PARTIAL_CHANGE 0x0020
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#define RBTXN_PREPARE 0x0040
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#define RBTXN_SKIPPED_PREPARE 0x0080
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#define RBTXN_HAS_STREAMABLE_CHANGE 0x0100
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/* Does the transaction have catalog changes? */
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#define rbtxn_has_catalog_changes(txn) \
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@ -207,6 +208,12 @@ typedef struct ReorderBufferChange
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((txn)->txn_flags & RBTXN_HAS_PARTIAL_CHANGE) != 0 \
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)
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/* Does this transaction contain streamable changes? */
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#define rbtxn_has_streamable_change(txn) \
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( \
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((txn)->txn_flags & RBTXN_HAS_STREAMABLE_CHANGE) != 0 \
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)
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/*
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* Has this transaction been streamed to downstream?
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*
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