From: Patrick Steinhardt <ps@pks.im>
To: git@vger.kernel.org
Cc: Junio C Hamano <gitster@pobox.com>, Han-Wen Nienhuys <hanwenn@gmail.com>
Subject: [PATCH v2 10/11] reftable/block: reuse zstream when writing log blocks
Date: Thu, 4 Apr 2024 07:48:46 +0200 [thread overview]
Message-ID: <26f422703ff6dfeb8de9d5a41af3d322b64e7706.1712209149.git.ps@pks.im> (raw)
In-Reply-To: <cover.1712209149.git.ps@pks.im>
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While most reftable blocks are written to disk as-is, blocks for log
records are compressed with zlib. To compress them we use `compress2()`,
which is a simple wrapper around the more complex `zstream` interface
that would require multiple function invocations.
One downside of this interface is that `compress2()` will reallocate
internal state of the `zstream` interface on every single invocation.
Consequently, as we call `compress2()` for every single log block which
we are about to write, this can lead to quite some memory allocation
churn.
Refactor the code so that the block writer reuses a `zstream`. This
significantly reduces the number of bytes allocated when writing many
refs in a single transaction, as demonstrated by the following benchmark
that writes 100k refs in a single transaction.
Before:
HEAP SUMMARY:
in use at exit: 671,931 bytes in 151 blocks
total heap usage: 22,631,887 allocs, 22,631,736 frees, 1,854,670,793 bytes allocated
After:
HEAP SUMMARY:
in use at exit: 671,931 bytes in 151 blocks
total heap usage: 22,620,528 allocs, 22,620,377 frees, 1,245,549,984 bytes allocated
Signed-off-by: Patrick Steinhardt <ps@pks.im>
---
reftable/block.c | 80 +++++++++++++++++++++++++++++++-----------------
reftable/block.h | 1 +
2 files changed, 53 insertions(+), 28 deletions(-)
diff --git a/reftable/block.c b/reftable/block.c
index e2a2cee58d..9129305515 100644
--- a/reftable/block.c
+++ b/reftable/block.c
@@ -76,6 +76,10 @@ void block_writer_init(struct block_writer *bw, uint8_t typ, uint8_t *buf,
bw->entries = 0;
bw->restart_len = 0;
bw->last_key.len = 0;
+ if (!bw->zstream) {
+ REFTABLE_CALLOC_ARRAY(bw->zstream, 1);
+ deflateInit(bw->zstream, 9);
+ }
}
uint8_t block_writer_type(struct block_writer *bw)
@@ -139,39 +143,57 @@ int block_writer_finish(struct block_writer *w)
w->next += 2;
put_be24(w->buf + 1 + w->header_off, w->next);
+ /*
+ * Log records are stored zlib-compressed. Note that the compression
+ * also spans over the restart points we have just written.
+ */
if (block_writer_type(w) == BLOCK_TYPE_LOG) {
int block_header_skip = 4 + w->header_off;
- uLongf src_len = w->next - block_header_skip;
- uLongf dest_cap = src_len * 1.001 + 12;
- uint8_t *compressed;
-
- REFTABLE_ALLOC_ARRAY(compressed, dest_cap);
-
- while (1) {
- uLongf out_dest_len = dest_cap;
- int zresult = compress2(compressed, &out_dest_len,
- w->buf + block_header_skip,
- src_len, 9);
- if (zresult == Z_BUF_ERROR && dest_cap < LONG_MAX) {
- dest_cap *= 2;
- compressed =
- reftable_realloc(compressed, dest_cap);
- if (compressed)
- continue;
- }
-
- if (Z_OK != zresult) {
- reftable_free(compressed);
- return REFTABLE_ZLIB_ERROR;
- }
-
- memcpy(w->buf + block_header_skip, compressed,
- out_dest_len);
- w->next = out_dest_len + block_header_skip;
+ uLongf src_len = w->next - block_header_skip, compressed_len;
+ unsigned char *compressed;
+ int ret;
+
+ ret = deflateReset(w->zstream);
+ if (ret != Z_OK)
+ return REFTABLE_ZLIB_ERROR;
+
+ /*
+ * Precompute the upper bound of how many bytes the compressed
+ * data may end up with. Combined with `Z_FINISH`, `deflate()`
+ * is guaranteed to return `Z_STREAM_END`.
+ */
+ compressed_len = deflateBound(w->zstream, src_len);
+ REFTABLE_ALLOC_ARRAY(compressed, compressed_len);
+
+ w->zstream->next_out = compressed;
+ w->zstream->avail_out = compressed_len;
+ w->zstream->next_in = w->buf + block_header_skip;
+ w->zstream->avail_in = src_len;
+
+ /*
+ * We want to perform all decompression in a single step, which
+ * is why we can pass Z_FINISH here. As we have precomputed the
+ * deflated buffer's size via `deflateBound()` this function is
+ * guaranteed to succeed according to the zlib documentation.
+ */
+ ret = deflate(w->zstream, Z_FINISH);
+ if (ret != Z_STREAM_END) {
reftable_free(compressed);
- break;
+ return REFTABLE_ZLIB_ERROR;
}
+
+ /*
+ * Overwrite the uncompressed data we have already written and
+ * adjust the `next` pointer to point right after the
+ * compressed data.
+ */
+ memcpy(w->buf + block_header_skip, compressed,
+ w->zstream->total_out);
+ w->next = w->zstream->total_out + block_header_skip;
+
+ reftable_free(compressed);
}
+
return w->next;
}
@@ -425,6 +447,8 @@ int block_reader_seek(struct block_reader *br, struct block_iter *it,
void block_writer_release(struct block_writer *bw)
{
+ deflateEnd(bw->zstream);
+ FREE_AND_NULL(bw->zstream);
FREE_AND_NULL(bw->restarts);
strbuf_release(&bw->last_key);
/* the block is not owned. */
diff --git a/reftable/block.h b/reftable/block.h
index 47acc62c0a..1375957fc8 100644
--- a/reftable/block.h
+++ b/reftable/block.h
@@ -18,6 +18,7 @@ license that can be found in the LICENSE file or at
* allocation overhead.
*/
struct block_writer {
+ z_stream *zstream;
uint8_t *buf;
uint32_t block_size;
--
2.44.GIT
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next prev parent reply other threads:[~2024-04-04 5:48 UTC|newest]
Thread overview: 49+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-04-02 17:29 [PATCH 0/9] reftable: optimize write performance Patrick Steinhardt
2024-04-02 17:29 ` [PATCH 1/9] refs/reftable: fix D/F conflict error message on ref copy Patrick Steinhardt
2024-04-03 18:28 ` Junio C Hamano
2024-04-02 17:29 ` [PATCH 2/9] refs/reftable: perform explicit D/F check when writing symrefs Patrick Steinhardt
2024-04-02 17:30 ` [PATCH 3/9] refs/reftable: skip duplicate name checks Patrick Steinhardt
2024-04-02 17:30 ` [PATCH 4/9] refs/reftable: don't recompute committer ident Patrick Steinhardt
2024-04-03 18:58 ` Junio C Hamano
2024-04-04 5:36 ` Patrick Steinhardt
2024-04-02 17:30 ` [PATCH 5/9] reftable/writer: refactorings for `writer_add_record()` Patrick Steinhardt
2024-04-02 17:30 ` [PATCH 6/9] reftable/writer: refactorings for `writer_flush_nonempty_block()` Patrick Steinhardt
2024-04-02 17:30 ` [PATCH 7/9] reftable/block: reuse zstream when writing log blocks Patrick Steinhardt
2024-04-03 19:35 ` Junio C Hamano
2024-04-04 5:36 ` Patrick Steinhardt
2024-04-02 17:30 ` [PATCH 8/9] reftable/block: reuse compressed array Patrick Steinhardt
2024-04-02 17:30 ` [PATCH 9/9] reftable/writer: reset `last_key` instead of releasing it Patrick Steinhardt
2024-04-04 5:48 ` [PATCH v2 00/11] reftable: optimize write performance Patrick Steinhardt
2024-04-04 5:48 ` [PATCH v2 01/11] refs/reftable: fix D/F conflict error message on ref copy Patrick Steinhardt
2024-04-04 5:48 ` [PATCH v2 02/11] refs/reftable: perform explicit D/F check when writing symrefs Patrick Steinhardt
2024-04-04 5:48 ` [PATCH v2 03/11] refs/reftable: skip duplicate name checks Patrick Steinhardt
2024-04-04 5:48 ` [PATCH v2 04/11] reftable: remove " Patrick Steinhardt
2024-04-04 5:48 ` [PATCH v2 05/11] refs/reftable: don't recompute committer ident Patrick Steinhardt
2024-04-04 5:48 ` [PATCH v2 06/11] reftable/writer: refactorings for `writer_add_record()` Patrick Steinhardt
2024-04-04 6:58 ` Han-Wen Nienhuys
2024-04-04 7:32 ` Patrick Steinhardt
2024-04-04 5:48 ` [PATCH v2 07/11] reftable/writer: refactorings for `writer_flush_nonempty_block()` Patrick Steinhardt
2024-04-04 5:48 ` [PATCH v2 08/11] reftable/writer: unify releasing memory Patrick Steinhardt
2024-04-04 7:08 ` Han-Wen Nienhuys
2024-04-04 7:32 ` Patrick Steinhardt
2024-04-04 9:00 ` Han-Wen Nienhuys
2024-04-04 11:43 ` Patrick Steinhardt
2024-04-04 5:48 ` [PATCH v2 09/11] reftable/writer: reset `last_key` instead of releasing it Patrick Steinhardt
2024-04-04 5:48 ` Patrick Steinhardt [this message]
2024-04-04 5:48 ` [PATCH v2 11/11] reftable/block: reuse compressed array Patrick Steinhardt
2024-04-04 7:09 ` [PATCH v2 00/11] reftable: optimize write performance Han-Wen Nienhuys
2024-04-04 7:32 ` Patrick Steinhardt
2024-04-08 12:23 ` [PATCH v3 " Patrick Steinhardt
2024-04-08 12:23 ` [PATCH v3 01/11] refs/reftable: fix D/F conflict error message on ref copy Patrick Steinhardt
2024-04-08 12:23 ` [PATCH v3 02/11] refs/reftable: perform explicit D/F check when writing symrefs Patrick Steinhardt
2024-04-08 12:24 ` [PATCH v3 03/11] refs/reftable: skip duplicate name checks Patrick Steinhardt
2024-04-08 12:24 ` [PATCH v3 04/11] reftable: remove " Patrick Steinhardt
2024-04-08 12:24 ` [PATCH v3 05/11] refs/reftable: don't recompute committer ident Patrick Steinhardt
2024-04-08 12:24 ` [PATCH v3 06/11] reftable/writer: refactorings for `writer_add_record()` Patrick Steinhardt
2024-04-08 12:24 ` [PATCH v3 07/11] reftable/writer: refactorings for `writer_flush_nonempty_block()` Patrick Steinhardt
2024-04-08 12:24 ` [PATCH v3 08/11] reftable/writer: unify releasing memory Patrick Steinhardt
2024-04-08 12:24 ` [PATCH v3 09/11] reftable/writer: reset `last_key` instead of releasing it Patrick Steinhardt
2024-04-08 12:24 ` [PATCH v3 10/11] reftable/block: reuse zstream when writing log blocks Patrick Steinhardt
2024-04-08 12:24 ` [PATCH v3 11/11] reftable/block: reuse compressed array Patrick Steinhardt
2024-04-09 0:09 ` [PATCH v3 00/11] reftable: optimize write performance Junio C Hamano
2024-04-09 3:16 ` Patrick Steinhardt
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